Abstract:
A rotating beacon employs an array of LEDs mounted on a rotor assembly in a pattern for unidirectional emission wherein the LEDs are excited through noncontact inductive coupling between a load coupling on the rotor assembly and a source coupling on the stator or mount element. In a particular embodiment, a primary sender flat coil of an air gap transformer is disposed concentrically forming a disc and mounted juxtaposed to a secondary receiver flat coil so that power can be conveyed across the air gap while the rotor is in motion. The transferred power excites substantially all of the LED array in a fixed pattern on the rotating mount. In a second embodiment, the air gap transformer has a primary sender coil is mounted coaxially with a secondary receiver coil (which is typically but not necessarily inside the primary coil), so the secondary, with the array can freely rotate and draw power from the source.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     NOT APPLICABLE  
       STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER  
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     NOT APPLICABLE  
       REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISC  
       [0003]     NOT APPLICABLE  
       BACKGROUND OF THE INVENTION  
       [0004]     This invention relates to beacon lamps or warning lamps, such as vehicle-mounted or point-of danger-mounted rotating lamps using light emitting diode (LED) arrays whereby a pattern of repeated flashes appear in a horizontal arc.  
         [0005]     In the past, rotating beacons have incorporated standard filament and bright halogen gas incandescent lamps. More recently, LED arrays of various configurations have been suggested for rotating beacon applications. A representative disclosure is found in U.S. Pat. No. 6,183,100. Therein are disclosed arrays of fixedly mounted LEDs disposed to be selectively excited or selectively excited and then reflected by either fixed mirrors, a single array LEDs disposed to have its output reflected by a rotating mirror, and arrays of rotatably mounted LEDs used to emit directly to a target. This last arrangement, shown in  FIG. 2A-2C  of U.S. Pat. No. 6,183,100, requires a commutator arrangement to allow continuous rotation of an array-bearing rotor. Consequently, the contacts are subject to degradation and possible failure, particularly after extended use or in harsh environments.  
         [0006]     Arrangements requiring large numbers of high output LEDs and complex switching schemes have certain disadvantages. For example, a single failure of one switching element may produce a dark area in the 360 degree warning coverage area. Further, large numbers of LEDs in arrays can prove to be unnecessarily expensive.  
         [0007]     What is needed is a LED-based rotating beacon which does not use unnecessary LED elements and is not hindered by the danger of electromechanical failure due to contact wear.  
       SUMMARY OF THE INVENTION  
       [0008]     According to the invention, a rotating beacon employs an array of LEDs mounted on a rotor assembly in a pattern for unidirectional emission wherein the LEDs are excited through noncontact inductive coupling between a load coupling on the rotor assembly and a source coupling on the stator or mount element. In a particular embodiment, a primary sender flat coil of an air gap transformer is disposed concentrically forming a disc and mounted juxtaposed to a secondary receiver flat shaped coil so that power can be conveyed across the air gap while the rotor is in motion. The transferred power excites substantially all of the LED array in a fixed pattern on the rotating mount. In a second embodiment, the air gap transformer has a primary sender coil mounted coaxially with a secondary receiver coil (which is typically but not necessarily inside the primary coil), so the secondary, with the array can freely rotate and draw power from the source.  
         [0009]     The invention will be better understood by reference to the following detailed description in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of an LED array mounted on a rotor inductively coupled to a source of power in a platform according to the invention.  
         [0011]      FIG. 2  is a side cross-sectional view of a first embodiment of a transformer driver.  
         [0012]      FIG. 3  is a side cross-sectional view of a second embodiment of a transformer driver.  
         [0013]      FIG. 4  is a circuit diagram of one embodiment of a circuit according to the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     The invention can be embodied in various forms, including in uses involving other types of illumination sources. However, the primary use is with LED arrays.  
         [0015]     Referring to  FIG. 1 , a perspective view of an LED array  10  is mounted on a rotor  12 . The rotor  12  has a bearing connection through the drive motor to a platform  14 . The platform  14  also typically carries an exciter circuit  16  that powers the LED array  10  through a coupling  18 , as hereinafter explained.  
         [0016]      FIG. 2  is a side cross-sectional view of a first embodiment of the coupling  18  in the form of a non-contact transformer driver with a primary winding  20  and a secondary winding  22 . The primary winding  20  is coupled to receive power from the exciter circuit  16  in the platform  14 . The secondary winding  22  is inductively coupled via an air gap  24  to the primary winding to draw power for the load, namely the LED array  10  ( FIG. 1 ). According to one embodiment of the invention, the primary winding  20  is a flat coil disposed concentrically forming a disc and mounted juxtaposed to the secondary winding  22 , the secondary winding being a flat coil for conveying power across the air gap  24  while the rotor  12  is in motion, the rotor  12  being mounted to a motor shaft  21 .  
         [0017]      FIG. 3  is a side cross-sectional view of a second embodiment of the coupling  18  according to the invention in the form of a non-contact transformer driver with a primary winding  120  and a secondary winding  122 . The primary winding  120  is coupled to receive power from the exciter circuit  16  in the platform  14  ( FIG. 1 ). The secondary winding  122  is inductively coupled via an air gap  124  to the primary winding  120  to draw power for the load, namely the LED array  10  ( FIG. 1 ). According to this embodiment of the invention, the primary winding  120  is a coil mounted on a first coil form  123  coaxially with the secondary winding  122  on a second coil form  125 , for conveying power in the magnetic field across the air gap  124  while the rotor  112  on the motor shaft  121  is in motion.  
         [0018]      FIG. 4  is a circuit diagram of one embodiment of a driver circuit  26  according to the invention. Driver circuit  26  is shown as including, in part, terminals Pos and Neg adapted to receive D.C. power from a power source (not shown), an oscillator circuit  40 , and a voltage regulator circuit  50 . Oscillator circuit  40  is shown as including resistors R 1 , R 2 , R 3 , R 4 , R 5 , diode D 4 , capacitor C 3  and a timing/oscillating integrated circuit (IC)  60 , such as the integrated circuit chip, model no. TLC555 available from Texas Instruments, located at 12500 TI Boulevard, Dallas, Tex., 75243-4136.  
         [0019]     Oscillator  40  starts to oscillate when current flows through resistors R 2 , R 4 , R 5 , and diode D 4  to the oscillating capacitor C 3  and charges this capacitor. When the voltage developing across capacitor C 3  reaches an internally preset voltage level, timing/oscillating circuit  60  discharges the voltage developed across capacitor C 3  via its terminal  7  and through resistor R 2 . This cycle is then repeated. As the level of applied voltage increases from, e.g., 9.8 to 58 D.C. volts in one exemplary embodiment, the current flows at a greater rate, which in turn, causes capacitor C 3  to charge in a shorter time period, thereby increasing the oscillation frequency. The internal preset voltage level determining when to discharge capacitor C 3  is independent of the applied voltage.  
         [0020]     The discharge path of the capacitor C 3  via terminal  7  of timing/oscillating circuit  60  and through fixed resistor R 2  makes the discharge time fixed over varying voltage inputs. The combination of the fixed discharge time and the varying charge time has the effect of narrowing the on-time (active time) of the pulse during each cycle. The pulse appears on terminal  3  of timing/oscillating circuit  60 . At 12 volts of supply, the pulse on terminal  3  has a relatively large on-time, up to 50% in one embodiment. At 24 volts, this on-time is almost half of its 12 volt level. Therefore, the on-time of this pulse deceases as the input voltage increases.  
         [0021]     The pulse at terminal  3  of timing/oscillating circuit  60 , which pulse is asymmetrical and a square-wave pulse, flows through diode D 2 . Diode D 2  is adapted to allow the gate of field effect transistor  32  to discharge to terminal  3  when there is no pulse (i.e., the pulse is inactive), thereby causing the field effect transistor  32  to go into a nonconductive state. Diode D 2  is adapted to block terminal  3  from directly charging the gate of transistor  32  during the on-time of the square-wave pulse. The active pulse at terminal  3  of timing/oscillating circuit  60  directly charges the gate of field effect transistor  34 , which, in turn, directly charges the gate of transistor  32  causing it to go into a conductive state. The charging of the gate terminal of transistor  32 , which causes transistor  32  to conduct, is performed by transistor  34 , which has a greater current handling capacity than terminal  3  of timing/oscillating circuit  60 . This increase in capacity speeds the transition from non-conduction to conduction of transistor  32 , thereby increasing efficiently. Diode D 3  provides proper bias for transistor  34 .  
         [0022]     Voltage regulator  50  that, in turn, is shown as including NPN Transistor  30 , resistor R 6 , diode D 5 , and capacitors C 2 , C 4 , provides a constant supply of voltage to the timing/oscillating circuit  60 . In some embodiments, voltage regulator  50  is adapted to supply to timing/oscillating circuit  60 , a constant voltage of e.g., 4 to 14 volts, as the input voltage between positive and negative supply terminals Pos and Neg varies from, e.g., 9.8 to 58 volts. Transistors  32 ,  34  as well as primary winding  20  or  120 , in part form, the output stage of driver circuit  26 . The load portion of the circuit, the LEDS or other illumination array which are mounted on the rotor  12  ( FIG. 1 ), is represented by the secondary winding  22  or  122  and an array  10  comprising a plurality of series strings of LEDs  52  connected in series-parallel combination.  
         [0023]     In operational theory, direct current at any level and supplied from, for example, a 12-48 volt system is applied between the positive terminal Pos and negative input terminal Neg of driver circuit  26 . Oscillator circuit  40  oscillates, creating square waves with a duty cycle controlled by the magnitude of the voltage level applied with decreasing ‘on’ time as increasing input voltage is applied. (This is a form of pulse width modulation). As described above, voltage regulator  50  supplies a fixed voltage source for timing/oscillating circuit  60  over the voltage range. Field effect transistor  32 , connected in series with the air core coil (primary sender coil  20 ), provides a path directly from positive voltage input terminal Pos to the negative voltage input terminal Neg. The air core coil  20  may be formed of several turns of wound copper wire on or off a bobbin, as shown for example in  FIGS. 2 and 3 .  
         [0024]     The pulse width modulated square wave power signal is delivered to the control element of the field effect transistor  32  (in this example the gate) either directly from timing/oscillating circuit  60  or through intermediate elements (Q 3  transistor  34 , and diodes D 2 , and D 3 ) in order to boost the square wave signal. In response to the pulse width modulated square wave, the field effect transistor  32  first conducts and then blocks current through the air core coil (primary sender coil). In response to the chopped current flowing through the air core coil, an electromagnetic field is created and allowed to decay. The field strength of the field is in direct proportion to the duty cycle of the pulse width modulated square wave created by the drive circuit IC, in the fashion of larger electromagnet field for longer on-time of the duty cycle. In this way, the field strength is maintained at a fixed level over the various levels of voltage applied to the drive circuit by different battery systems or power sources.  
         [0025]     A second air core coil (secondary receiver coil  22  or  122 ) is connected in series with the array  10  formed of a plurality of series strings of LEDs connected in parallel. Alternatively, fluorescent tubes may be used. This connection forms a closed circuit with the secondary winding  22  of the air core coil.  
         [0026]     When the secondary winding  22  is brought to close proximity to the primary air core coil, the decaying electromagnet field across the primary air core coil is induced (through transformer action) across the secondary air core coil, thereby energizing the load of light emitting diodes in array  10 . The two coils  20 ,  22  in this fashion form an air core transformer whose primary and secondary coils may physically move freely within each other&#39;s electromagnetic fields without brushes or mechanical wear.  
         [0027]     The electromagnetic field of the primary air core coil  20  is controlled in strength, thus is the induced field across the secondary  22  also controlled, thereby maintaining proper energy to the light emitting diodes, which benefit from the pulse nature of the cycling energy of the building and decaying electromagnet field. The particular benefit is increased usable light from the light emitting diodes with less heat generation. For a portion of the time (as the field reverses itself), the light emitting diodes are de-energized. The human eye does not perceive this cycle if high enough in frequency and thus rather perceives a constant light. The portion of the time that energy is applied, it is in a high current pulse form, thus giving more light output per unit of time.  
         [0028]     Light emitting diodes suffer from heat build up. The two air core coils are free to move or rotate within the confines of the electromagnetic field and still transmit energy from one to the other; the secondary air core coil  22  is driven via a motor (not shown) to rotate within a housing (not shown), thereby passing air over the individual light emitting diodes, cooling them, and providing for a rotating beacon.  
         [0029]     The secondary air core coil  22  is free to rotate within the confines of the electromagnetic field of the primary  20  and still receive energy; no brushes or other mechanical connection is required to pass power from the moving to non-moving segments of this structure, a beacon, removing the need for a carbon brush, which has a limited lifetime due to wear. Using a direct drive stepper motor further enhances product life by eliminating the carbon brushes in the motor itself.  
         [0030]     The invention has been explained with reference to specific embodiments. Other embodiments will be evident to those of ordinary skill in the art. Therefore, it is not intended that the invention be limited except by the appended claims.