POSTAL TRACKING SYSTEM
First Claim
1. A tracking system comprising a. a passive transponder having 1. a Receiving antenna lying in a plane and responsive principally to radiation polarized in said plane, and 2. means for transmitting signals when activated by the radiation received by said antenna, b. means for activating said transponder when it is located in a region including a transmitting antenna array for radiating signals in three planes orthogonal to each other to provide a radiation pattern in said region in said receiving antenna plane, and c. means for receiving signals transmitted from said transponder so as to track said transponder when it is located in said region.
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Accused Products
Abstract
A system for tracking mail bags, letters, and parcels through a post office to determine mail processing times accurately as well as processing delays is disclosed. An unobtrusive transponder in the form of a card is located in letters or mail bags to be tracked. A number of stations are located along the route of the mail bags and irradiate these bags. Each station includes an array of three antennas disposed in mutually orthogonal relationship so as to irradiate the transponder notwithstanding its position. When irradiated by ultra high frequency (UHF) energy, the transponder is activated and transmits a VHF signal. The transponder includes a transmitting circuit which may be selectively set to transmit a signal having a frequency uniquely identifying the transponder. The system includes a receiver for tracking a plurality of transponders and providing an output as to when and if the transponder is tracked as it passes through each station along the mail route.
126 Citations
28 Claims
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1. A tracking system comprising a. a passive transponder having 1. a Receiving antenna lying in a plane and responsive principally to radiation polarized in said plane, and 2. means for transmitting signals when activated by the radiation received by said antenna, b. means for activating said transponder when it is located in a region including a transmitting antenna array for radiating signals in three planes orthogonal to each other to provide a radiation pattern in said region in said receiving antenna plane, and c. means for receiving signals transmitted from said transponder so as to track said transponder when it is located in said region.
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2. The invention as set forth in claim 1 wherein said passive transponder includes a card which defines the plane in which said receiving antenna lies.
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3. The invention as set forth in claim 2 wherein said antenna is a body of conductive material on a portion of said card.
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4. The invention as set forth in claim 1 wherein said transponder includes a detector circuit coupled to said receiving antenna for providing operating power when said receiving antenna is irradiated by said transmitting antenna signals in the UHF band, and wherein said transmitting means includes an oscillator operative in the VHF band when activated by said operating power.
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5. The invention as set forth in claim 4 wherein receiving antenna includes a plurality of dipole elements on the surface of a card, both of which are connected to said detector.
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6. The invention as set forth in claim 5 wherein said oscillator includes a plurality of coils on the surface of said card, said coils being connected to said oscillator.
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7. The invention as set forth in claim 4 wherein said oscillator includes a tank circuit having a coil on the surfaces of a card, which coil provides a transmitting antenna for said transponder.
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8. The invention as set forth in claim 7 wherein said coil includes a pair of sections each on an opposite surface of said card, and means extending through said card and intersecting said sections of said coil for selectively changing the inductance of said coil and thereby the frequency of the signal transmitted by said oscillator.
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9. The invention as set forth in claim 1 wherein said transmitting antenna array includes three transmitting antennas spaced from each other along the perimeter of said region.
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10. The invention as set forth in claim 9 wherein each of said transmitting antennas comprises a card having a radiating element disposed in the plane of said card and parallel to an edge thereof.
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11. The invention as set forth in claim 10 wherein each of said cards is disposed in different ones of three mutually perpendicular planes.
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12. The invention as set forth in claim 11 comprising a mast on which said cards are mounted.
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13. The invention as set forth in claim 12 wherein said mast has a vertical section and a horizontal section respectively disposed on adjacent sides of said region, at least two of said cards being mounted on one of said sections.
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14. The invention as set forth in claim 14 wherein said two cards are mounted on said horizontal section.
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15. The invention aS set forth in claim 10 wherein said card has a director element along one edge thereof and a reflector element on the opposite edge thereof, said radiating element being disposed between said edges and parallel thereto.
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16. The invention as set forth in claim 15 wherein said radiating element has first and second parallel branches spaced from each other and connected together at one end, said first of said branches having a free end terminating a distance from the end thereof which is connected to said second branch about at the mid-point of said second branch, a coaxial feed through connector having a center conductor connected to the free end of said first branch and an outer conductor connected to the mid-point of said second branch.
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17. A passive transponder comprising a. a card of insulating material, b. a receiving circuit for translating radiation into operating power mounted on said card, said receiving circuit including a receiving antenna disposed on a surface of said card, and c. an oscillator circuit also mounted on said card and having said operating power coupled thereto, said oscillator circuit including a tank circuit having capacitor and inductor elements, said inductor element including first and second branches disposed on opposite surfaces of said card, said capacitor including a plurality of plates disposed on said opposite surfaces of said card, said card providing the dielectric of said capacitor, and openings for conductive members, said openings extending through said card between said branches for changing the inductance of said inductor element.
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18. The invention as set forth in claim 17 wherein said inductor element provides a transmitting antenna for said transponder.
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19. The invention as set forth in claim 18 wherein said capacitor element includes a pair of top plates on a first surface of said card, said plates being spaced from each other to provide a gap therebetween, and a bottom plate disposed on a second surface of said card in the region opposite to said gap whereby to provide first and second capacitors respectively between the first of said pair of top plates and said bottom plate and between the second of said pair of top plates and said bottom plate.
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20. The invention as set forth in claim 19 wherein said plates are printed upon said surfaces of said card.
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21. The invention as set forth in claim 20 including a conductive member disposed on said second surface of said card in contact with said bottom plate and extending transversely across the region of said second surface opposite to said first and second plates whereby to vary the capacitance of said capacitor elements.
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22. The invention as set forth in claim 18 wherein said branches are each loops which overlie each other, a first on the top and a second on the bottom surface of said card, a plurality of spaced fingers extending in opposite direction from opposite sides of said top surface and bottom surface loops each toward the center of said card on their respective surfaces and overlying each other at the center of said card, and means for selectively interconnecting said fingers and said loops where they overlie each other for selectively changing the inductance of said inductor element and the frequency of said oscillator.
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23. The invention as set forth in claim 22 wherein said loops are printed on said top and bottom surfaces.
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24. The invention as set forth in claim 18 wherein said capacitor elements include a plate on the bottom surface of said card, and a pair of plates on the top surface of said card, said pair of top plates each including a conductor located along an edge of said bottom plate and spaced therefrom, and a plurality of L-shaped fingers disposed in nested relationship and extending from said conductor into a region of said card overlying said bottom plate, and means for disconnecting the free legs of each of said L-shaped members from the leg thereof extending to said conductor whereby to vary the capacitance of said elements and thereby change the frequency of said oscillator.
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25. In a tracking system operative for tracking a plurality of transponders which transmit signals at different frequencies in a band, a receiving system for simultaneously tracking said transponders at successive time intervals, said receiving system comprising means for transmitting a high and a low reference signals having frequencies at opposite ends of said band, a receiver including a frequency translator for receiving said reference signals and said transponder signals and mixing therewith an injection signal to provide an output, means for sweeping said injection signal in frequency at said successive time intervals so as to provide said outputs whenever a transponder or reference signal is received during each of the sweeps, and means responsive to said output for indicating the reception of Said signals during each of said sweeps.
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26. The invention as set forth in claim 25 wherein said indicating means is a oscilloscope.
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27. The invention as set forth in claim 25 wherein said indicating means comprises a clock pulse source, a counter for counting clock Pulses from said source, means for enabling the application of said clock pulses to said counter when said output corresponds to said low reference, and means for reading out said counter when said output corresponds to said transponder and high reference signals to indicate the presence of said signals.
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28. The invention as set forth in claim 27 including a comparator having storage for counts corresponding to said signals, means for applying the output of said counter to said comparator when said output corresponding to said high reference signals is produced whereby to obtain an error signal, and means responsive to said error signal for varying the frequency of said injection signal.
Specification