WO1989006367A1

WO1989006367A1 - File location system

Info

Publication number: WO1989006367A1
Application number: PCT/US1989/000093
Authority: WO
Inventors: Lawrence D. Korn; Russell C. Harbaugh
Original assignee: Korn Lawrence D; Harbaugh Russell C
Priority date: 1988-01-11
Filing date: 1989-01-11
Publication date: 1989-07-13
Also published as: AU3031289A

Abstract

A file location system is disclosed having a transponder (10) which momentarily transmits an encoded radio signal with a selected one of a plurality of different codes. A responder (30) is attached to each file in the file location system and includes a radio receiver for receiving the encoded radio signal from the transponder (10) and for comparing the encoded radio signal with a preset code unique to each responder (30) and thus unique to each file in the file location system. The responder (30) having a preset code matching the encoded signal from the transponder transmits a responsive radio signal back to the transponder. The signal strength and/or time differential of the signal from the transponder received at each of the four antennas is thereafter correlated and, through triangulation, the position of the responder relative to the transponder antennas (102, 104) is determined.

Description

FILE LOCATION SYSTEM Background of the Invention

I. Field of the Invention

The present invention relates generally to a transponder-responder system and, more particularly, to such a system for use in a file location system.

II. Description of the Prior Art

The location of individual files in any modern office presents a continuing and perplexing problem. Even though such files are conventionally stored in a common or central file area, numerous files are constantly removed from the central file system when work on the particular file so dictates. Once removed from the central filing area, it frequently is difficult and time consuming to again find the file since it may be in one of many different locations.

There have been numerous attempts to devise systems for maintaining the particular location of each individual file so that the files can be rapidly located as required. These previously known file location systems include, for example, a card catalog which is maintained in the central filing area and on which each person "checks out" a file as it is removed from the central filing area. This previously known practice, however, is both cumbersome and somewhat ineffective in operation. This is particularly true when the file, once removed by a person from the central filing area, is transferred to other locations in the office before the file is finally returned to the central filing area.

Summary of the Present Invention The present invention provides a file location system which overcomes all of the above mentioned disadvantages of the previously known practices. In brief, the file location system of the present invention comprises a transponder having means for encoding a radio signal with a selected one of a plurality of codes wherein one code is assigned to each individual file. The transponder, when activated, momentarily transmits an interrogation pulse of the selected encoded radio signal into the working area where the file is located.

A responder is attached to each individual file in the file system. Each responder comprises a radio receiver for receiving the interrogation pulse from the transponder transmitter. Means in the responder then compare the code of the encoded radio signal of the interrogation pulse with a preset code which is unique for each responder and thus unique for each file. In the event that the encoded radio signal from the transponder matches the preset code at the responder, the responder transmits a response signal which is received by a receiving antenna system associated with the transponder.

The receiving antenna system for the transponder preferably includes a plurality of spaced apart antennas, each of which receives the response signal from the responder. The transponder further includes means for comparing the relative signal strength and/or time differential of the responder signal as it is received by each individual receiving antenna for the transponder and, once correlated, the transponder provides an output signal representative of the position of the responder, and thus of the file, with respect to the transponder receiving system.

In the preferred form of the invention, the responder is passive, i.e., does not contain an individual active power source. Instead, the responder preferably converts a part of the power from the interrogation pulse and then utilizes that power, once the preset signal matches the encoded radio signal, to power the transmitter at the responder. Alternatively, however, the responder can have other power means, such as solar power means or an active battery.

Brief Description of the Drawing A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which:

FIG. 1 is a block diagrammatic view illustrating a preferred embodiment of the transponder portion of the present invention?

FIG. 2 is a block diagrammatic schematic view illustrating a preferred embodiment of the responder of the present invention; and

FIG. 3 is a view similar to FIG. 2 but illustrating a modification thereof.

Detailed Description of a Preferred Embodiment of the Present Invention

With reference first to FIG. 1, a preferred embodiment of the transponder 10 of the present invention is thereshown and comprises an PF escalator 12 which generates a radio signal at its output 14. Preferably, the radio signal on output 14 is in one of the ISM bands, e.g. 2.45 GHz or 13.5 GHz where the transmission of relatively high power signals is permitted without the need for a license.

The RF output signal on line 14 is fed as an input signal to a modulator/amplifier 16. The modulator/amplifier 16 also receives as a modulating signal the output from a code input device 18 which is fed through an encoder 20 and to the modulator/amplifier. The code input device 18 is preferably a personal computer or keyboard which selects one of a plurality of different codes wherein each responder in the file location system has a unique code so that the selected code corresponds to a single responder. The encoder 20, which can be of any conventional construction, then modulates the RF signal from the oscillator 12 at the modulator/amplifier 16 in accordance with the selected code from the input device 18 so that the modulator/amplifier 16 momentarily produces an encoded interrogation pulse on its output line 22.

An output line 22 from the modulator/amplifier 16 is connected to a transmitting antenna 24 for the transponder 10. The transmitting antenna 24 has a fixed location with respect to the building or office in which the file location system is employed.

With reference now to FIG. 2, one responder 30 of the file location system is thereshown in greater detail. It will be understood, of course, that the file location system includes a plurality of responders 30 wherein one responder 30 is attached by any conventional means to each file. Furthermore, as will be subsequently described in greater detail, a unique code is assigned to each responder 30 i n th e f i l e loca tion system.

Still referring to FIG. 2, the radio signal from the transponder antenna 24 is received by a receiving antenna 32 in each responder having its output 34 connected as an input signal to a filter 36. The filter 36 rejects unwanted signals, such as harmonics, in the conventional fashion and feeds a filtered radio signal on its output 38 which is representative of the signal transmitted by the transponder antenna 24. The filter output is coupled through a resistor 40 as an input signal to a detector/decoder

42. The detector/decoder 42 demodulates the radio signal and generates a decoded radio signal on its output 44.

The output 44 from the detector/decoder 42 is connected as one input signal to a comparator 46. Simultaneously, the output 48 from a memory 50 containing the preset code for that particular responder 30 is connected as a second input signal to the comparator 46. In the event of a match between the demodulated signal on output 44 and the preset coded signal from the memory 50, the comparator 46 generates a signal on its output 52 which is connected as an input signal to an RF amplifier 54.

Conversely, if the demodulated or decoded signal on the detector/decoder output does not match the preset encoded signal in the memory 50, the comparator 46 does not generate any signal on its output 52. In this event, the comparator 46 does not produce an output signal to the amplifier 54 so that the amplifier remains inactive.

Still referring to FIG. 2, the output 38 from the filter 36 is also connected as an input signal to a reference detector/PF oscillator 60 having its output 62 connected as an input to the RF amplifier 54. The output 62 from the reference detector/RF oscillator 60 locks the carrier frequency of the amplifier 54 to the frequency of the interrogation pulse from the transponder 10.

The output from the amplifier 54 is connected to a transmit antenna 64. A signal is transmitted by the antenna 64 only in the event that the encoded radio signal received by the antenna 32 at the responder matches the preset code in the memory 50; otherwise, no signal is transmitted by the responder. In this fashion, it will be appreciated that for a given code, only one transponder of the plurality of transponders in the file location system transmits a response signal on its antenna 64 after receipt of the coded signal on its reception antenna 32.

Still referring to FIG. 2, in the preferred form of the invention, the responder 30 is passive, i.e. it does not contain an active power supply. Instead, the output 34 from the reception antenna 32 is preferably connected through a resistor 70 and diode 72 to provide a DC power output at terminal 74. A capacitor 76, as well as a zener diode 78 are also connected in parallel between the terminal 74 and ground 80. The capacitor 76 forms a voltage storage device in the well known fashion while the zener diode 78 maintains the voltage at the terminal 74 at or below a preset value.

With reference now to FIG. 3, alternatively a solar cell 82 is used to power the responder 30.

Still referring to FIG. 2, preferably a pair of back to back zener diodes 90 and 92 are connecte^d across the output from the resistor 40 and ground 94. These diodes 90 and 92 provide surge protection for the responder 30.

With reference again to FIG. 1, the transponder 10 further comprises at least two and preferably four receiving antennas 100, 102, 104 and 106. These antennas 100-106 are physically separated from each other and are preferably in the shape of a rectangle with one antenna 100-106 at each corner of the rectangle. Furthermore, as shown in FIG. 1, the transponder transmit antenna 24 is preferably at the center of the rectangle although other locations as well as multiple transmit antennas can also be used. Still referring to FIG. 1, the output from each antenna 100-106 is connected through a detector/amplifier 108, 110, 112 and 114, respectively, so that the strength of the output from each of the four detectors 108-114 is representative of the strength and/or time differential of the response siσnal received by its associated antenna 100-106 from the transmitting or responding responder 30. Such space diversity antennas are well known to those having ordinary skill in the art so that a further description is unnecessary. In the well known fashion, as the transmitting responder becomes closer to any individual antenna, the strength of the response signal received by the antenna 100-106, and thus the output from its associated detector/amplifier 108-114 will increase, and vice versa.

Still referring to FIG. 1, the outputs from the detectors 108 and 112, i.e. the detectors 108 and 1.12 associated with the antennas 100 and 104 at opposed corners of the rectangle, are connected as input signals to a first comparator 120. Similarly, the output signals from the other detectors 110 and 114 associated with the other two antennas 102 and 106 at the remaining opposed corners of the rectangle are connected as input signals to a second comparator 122.

The output 124 from the comparator 120 is thus proportional to the relative position of the transmitting responder as between the two antennas 100 and 104. Similarly, the output 126 from the second comparator 122 is representative of the relative position of the transmitting responder between the other two antennas 102 and 106.

The outputs 124 and 1?6 from the comparators 120 and 122, respectively, are connected respectively as input signals to two filters 128 and 130 which provide a filtered output on their outputs 132 and 134, respectivley, to a position indicating device 136. The operation of the position indicating device will be subsequently described in greater detail. The comparators 120 and 122 also contain conventional circuitry for comparing the time differential between the signals received on the antennas 100, 102, 104 and 106. This time differential signal is utilized to determine the position of the responder through triangulation.

Still referring to FIG. 1, a delay circuit 140 is electrically connected in between the output 14 from the RF oscillator 12 and an input signal to each of the filters 128 and 130. The delay circuit 140 thus produces a signal on its output 142 a short time period after the transmission of the interrogation pulse from the transponder antenna 24. This delay corresponds to the expected delay between the transmission of the interrogation pulse by the transponder 10 and the receipt of the response signal from the responder 30 by the transducer antennas 100-104 as well as internal circuit delays in both the responder 30 and transponder 10. Thus, the delay 140 acts to pass the signal from the comparator outputs 124 and 126 through the filters 128 and 130 only when the reception of a response signal from one of the responders is expected.

Still referring to FIG. 1, each comparator 120 and 122 also preferably includes a null circuit 150 and 152, respectively. The null circuits 150 and 152 are utilized to eliminate transients and the like.

The position indicator 136 preferably comprises at least two analog/digital convertors which convert the output signals on the outputs 132 and 134 from the filters 128 and 130 into digital signals. These digital signals are then processed as input signals by a computing system, such as a personal computer. The personal computer is programmed in any conventional fashion to indicate the position of the transmitting responder with respect to the antennas 100-106 through triangulation. Such triangulation is possible since the output 124 from the comparator 122 is representative of the position of the responder with respect to a transverse line extending in between the antennas 100 and 104. Similarly, the output 126 from the second comparator 122 is representative of a transverse line extending between the antennas 102 and 106. The intersection of these two transverse lines is representative of the transmitting responder, i.e. the responder, whose preset code matches the code signal transmitted by the transponder.

Having described my invention, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims. I claim;

Claims

CL A I MS

1. A file location system comprising a transponder comprising: means for encoding a radio signal with a selected one of a plurality of codes, means for transmitting said selected encoded radio signal, a plurality of responders, each responder having a unique preset code, each responder comprising: a radio receiver for receiving the selected encoded radio signal from said transponder transmitter, means for comparing the code of said received signal with a preset code in said transponder and for generating a match signal only when said preset code matches the code of said received signal, means responsive to said match signal for transmitting a response signal from said responder, said transponder further comprising means for receiving said response signal and for generating location signal representative of the location of said transponder transmitting said response signal; wherein said transmitting means simultaneously transmits said encoded radio signal to a plurality of said responders.

2. The invention as defined in claim 1 wherein said responder further comprises means for converting a portion of said received radio signal to electrical power and for storing said electrical power, means for utilizing said stored electrical power as the sole electrical power source for said transponder.

3. The invention as defined in claim 2 wherein said receiving means comprises an antenna and wherein said converting means comprises a capacitor having one side electrically connected to one side of the antenna and a resistor electrically connected between the other sides of said antenna and said capacitor.

4. The invention as defined in claim 3 and comprising a diode in series with said resistor.

5. The invention as defined in claim 1 wherein said responder comprises a power supply having a solar powered cell.

6. The invention as defined in claim 1 wherein said means for generating said location signal comprises a plurality of discrete receiving antennas which are physically spaced apart from each other and means for determining the relative strength of the response signal received by each of said discrete antennae.

7. The invention as defined in claim 6 wherein said transponder transmitting antenna is positioned at a midpoint between said transponder receiving antennae.

8. The invention as defined in claim 7 and comprising four transponder receiving antennae, one transponder receiving antenna being positioned at each corner of a rectangle, said transponder transmitting antenna being positioned at a midpoint of said rectangle.

9. The invention as defined in claim 8 wherein said location signal generating means comprises means for generating a first comparison signal representative of the difference in received signal strength from two transponder receiving antennae in two opposed corners of said rectangle, means for generating a second comparison signal representative of the difference in received signal strength from the other two transponder antennae, and means responsive to said comparison signals for generating said location signal.