WO2007091258A2

WO2007091258A2 - Object tracking system

Info

Publication number: WO2007091258A2
Application number: PCT/IL2007/000161
Authority: WO
Inventors: Eran Tuval
Original assignee: Pure Rf Ltd.
Priority date: 2006-02-08
Filing date: 2007-02-07
Publication date: 2007-08-16
Also published as: WO2007091258A3; IL173607A0

Abstract

The invention provides a system and method for tracking one or more objects (11). The system of the invention includes tags (2) that are attached to the objects to be tracked that transmit a signal. Antenna modules (10) receive the signals transmitted by the tags and inputs the signals into a processor (8). The processor calculates from the signals a current location of each tag and then compares the current location of the tag with one or more previously calculated locations of the tag to determine whether the tag is undergoing any movement.

Description

OBJECT TRACKING SYSTEM

FIELD OF THE INVENTION

The invention relates to systems for continuously tracking objects.

BACKGROUND OF THE INVENTION

Various types of systems and methodologies are known for tracking objects. In one method, a radio frequency (RP) transmitting tag is attached to each of the objects to be tracked. The tag signals are received and analyzed in order to obtain positional information on the objects.

US Patent No. 6,958,677, for example, discloses an object location monitoring system in which beacons are spatially distributed throughout an area to be monitored. The beacons transmit interrogation signals that are received and echoed by transponders in tags attached to objects being tracked. The time difference between the interrogation signal and the echo reflects the signal propagation time and thus the distance between the beacon and the transponder. A triangulation method is used to determine the location of each transponder based on the transponder's distances from the beacons. US Patent No. 6,989,741 discloses a system in which a base station transmits and receives signals at multiple frequencies. The transmitting and receiving of signals between the base station and a tag allows the base station to track the object to which the tag is attached. The distances frpm the base station are divided into zones with the lowest numbered zone being closest to the base station and the highest numbered zone being farthest away from the base station.

US Patent No. 6,483,427 discloses a system in which cell controllers with multiple antenna modules generate a carrier signal received by the tags. The tags shift the frequency of the carrier signal, modulate an identification code onto it, and transmit the resulting tag signal at randomized intervals. The antennas receive and process the response, and determine the presence of the tags by proximity and triangulation. The distance of a tag from an antenna is calculated by measuring the round trip signal time.

SUMMARY OF THE INVENTION The present invention provides a system and method for tracking the movement of an object. In accordance with the invention, an object to be tracked is periodically located. The current location of the object is compared with its location at one or more times in the recent past in order to determine whether or not the objection is undergoing any movement. The object is then classified according to the type of motion the object is undergoing.

One embodiment of the system of the invention comprises one or more radio frequency tags each of which is configured to be attached to an object to be tracked. A central processing unit (CPU) continuously detects signals transmitted by the tags by means of two or more antenna modules. The CPU receives data and information collected by the antenna modules and stores the data in a memory. The CPU includes a processor configured to analyze the input data, in order to determine which, if any, of the tagged objects are currently undergoing motion, and to determine a status for each tagged object based upon its current motion.

In one embodiment of the method of the invention, the current distance between each tag and each of one or more of the receiving antenna modules is calculated. The current location of each tag is then • calculated, for example, using triangulation techniques, based upon the distance of a tag from three or more of the antenna modules. The current location of each of the ta'gs is compared with the tag's location in the recent past as previously calculated and stored in the memory. Then it is determined for each of the tags, based upon the comparison of a tag's current location and its location in the recent past, whether or not the tag is currently undergoing any motion. The tag is then assigned a status according to its current motion. In a preferred embodiment, the tags are assigned to one of three statuses according to their current motion. A tag that is not currently undergoing any motion is assigned a first status referred to herein as "green status". A tag that is currently undergoing motion within a predetermined space is assigned a second status referred to herein as "yellow status". A tag that is currently undergoing motion outside the space is assigned a third status referred to herein as "red - J -

statiis". When a tag having the red status is identified, an alarm may be sounded in order to alert security personnel of the motion of the object.

Thus, in one of its aspects, the invention provides a system for tracking one or more objects comprising: (a) One or more tags transmitting a signal, each tag being configured to be attached to an object to be tracked;

(b) Two or more antenna modules receiving signals transmitted by the tags; and

(c) A processor configured, for each of one or more tags, to: i calculate from signals received by the antenna modules a current location of the tag; and ii compare the current location of the tag with one or more previously calculated locations of the tag and to determine a status of the tag on the basis of the comparison. In another of its aspects, the invention provides method for tracking one or more objects comprising:

(a) attaching to each of the objects a tag transmitting a signal,

(b) receiving signals transmitted by the tags; and

(c) for each of one or more of the tags: (a) calculating from the received signals a current location of the tag;

(b) comparing the current location of the tag with one or more previously calculated locations of the tag; and

(c) determining a status of the tag on the basis of the comparison.

In yet another of its aspect^'s, the invention provides a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for tracking one or more objects, each object being attached to a tag transmitting a signal, comprising, for each of one or more of the tags,: (a) Calculating, from signals received from the tag, a current location of the tag;

(b) comparing the current location of the tag with one or more previously calculated locations of the tag; and (c) determining a status of the tag on the basis of the comparison.

In still another of its aspects, the invention provides a computer program product comprising a computer useable medium having computer readable program code embodied therein for tracking one or more objects, each object being attached to a tag transmitting a signal, the computer program product comprising: computer readable program code for causing the computer, for each of one or more of the tags, to calculate from signals received from the tag, a current location of the tag; computer readable program code for causing the computer to compare the current location of the tag with one or more previously calculated locations of the tag; and computer readable program code for causing the computer to determine a status of the tag on the basis of the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, a preferred^" embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 -shows a schematically a system for tracking objects in accordance with one embodiment of the invention;

Fig. 2 shows the system of Fig. 1 deployed in a three dimensional space; and Fig. 3 shows a method for object tracking in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. 1 shows schematically an object tracking system 1 in accordance with one embodiment of the invention. The system 1 comprises one or more radio frequency tags

2 each of which is configured to be attached to an object to be tracked. Three tags 2a, 2b and 2c are shown in Fig. 1. This is by way of example only, and the system of the invention may comprise any number of tags 2. - -> -

In one embodiment, the tags 2 periodically transmit a radio-coded unique identity code (UID) 14. A central processing unit (CPU) 8 detects the signals transmitted by the tags 2 by means of two or more antenna modules 10 connected to the CPU 8 through respective cables 12. In another embodiment, the tags 2 do not generate their own radio signal. Rather, the antenna modules 10, transmit, in succession, a direct sequence spread spectrum interrogator signal 22 at a first frequency. Each tag 2 receives this signal 22, modulates its UID code onto the signal 22, and immediately transmits back to the CPU 8 a frequency-shifted signal 24. In this embodiment, each antenna module 10 has a transmit antenna and a receive antenna. The CPU 8 collects data and information collected by the antenna modules 10 and stores the data in a memory 17. The CPU 8 includes a processor 16 configured to analyze the input data, as described below in order to determine a status for each to the objects to which a tag 2 has been attached. The results of the analysis may be displayed on a display screen 21. The processor 16 may be configured to generate a sensible signal, such as sounding an alarm 19 when one or more of the objects has any one of one or more predetermined statuses.

Fig. 2 shows the object tracking system 1 disposed at a site including in a defined three dimensional space 6. The space 6 may be a room, as shown in Fig. 2. Alternatively, the space 6 may be two or more rooms located in the same building, or two or more rooms located in different buildings. Each of the tags 2 has been attached to a respective- object 11 to be tracked. Four antenna modules lOa, 10b, 10c, and 1Od are shown in Figs 1 and 2. This is by way of example only, and the system 1 may be implemented with any number of antenna modules 10 that provide complete coverage of the predefined space 6 when distributed in the space 6. One or more of the antenna modules 10, such as the antenna modules 10a, 10b, and 10c may be attached to a suspended ceiling 22. One or more of the antenna modules 10, such as the antenna module 1Od may be positioned outside the space 6 in order to follow movement of an object after the object has been removed from the space 6. The CPU 8 may be located outside the space 6, as shown in Fig. 2. The cables 12 may be included into a common cable 13 from the space 6 to the CPU 8. A portion of the cables 12 or the common cable 13 may be located above the suspended ceiling 22.

Tag signals 14 or 24 (Fig. 1) transmitted by the tags 2, are received by one or more of the antenna modules 10, and is processed by the processor 16. Fig. 3 shows a flow chart for the processing earned out by the processor 16. The process begins with the most recent signals received from the antenna modules being input to the processor 16 (step 30) and then stored in the memory 17 (step 32). In step 34, the current distance between each tag 2 and each of one or more of the antenna modules 10 is calculated. In an embodiment in which the tags 2 periodically and spontaneously transmit a radio- coded unique identity code (UID) signal 14, the distance between the tag and each of the antenna modules 10 can be calculated from the intensity of the transmitted signal 14. In an embodiment in which the antenna modules 10 transmit, in succession, a direct sequence spread spectrum interrogator signal 22 and each tag 2 receiving the signal 22 transmits back a frequency- shifted signal 24, the distance from the transmitting antenna module 10 to the tag 2 can be calculated by the processor 16 from- the round trip time of transmission. The processor 16 switches among the antenna modules 10 to obtain the distance from each tag 2 to each of antenna modules 8.

In step 36, the processor 16 calculates the location of one or more of the tags 2 in the space 6. This may be done, for example, using triangulation techniques based upon the distance of a tag from three or more of the antenna modules 10. The location of a tag 2 in the space 6 may be specified' by providing three dimensional coordinates of the tag in the space 6, for example the distance of the tag from the floor 30, the wall 26 and the wall 28. In step 38, the current location of one or more of the tags is compared with the tag's location in the recent past as previously calculated and stored in the memory 17. For example, the current location of a tag could be compared to its location or locations previously determined during the preceding two seconds. Then in step 40 it is determined for each of one or more tags, based upon the comparison of a tag's current location and its location in the recent past, whether or not the tag is currently undergoing any motion. For a tag that is currently stationary, the process continues with step 42 with the tag's status being set to "green status". For a tag that is currently undergoing motion, the process continues with step 44 where it is determined whether the tag is moving within the space 6. For a tag undergoing motion within the space 6, the process continues with step 46 with the tag's status being set to "yellow status". For a tag that is currently undergoing motion outside the space 6, the process continues with step 48 with the tag's status being set to "red status". When a tag having the red status is identified, the process continues with step 50 in which the alarm 19 is sounded in order to alert security personnel of the motion of the object. The alarm 19 may also be sounded if the presence of any one of the tags 2 is not detected by any of the antenna modules 10. This might occur if the tag was tampered with. The current status of any one or more of the tag's may then be displayed on the display screen 19.

It will also be understood that the system according to the invention may be a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing the method of the invention. The invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention.

Claims

CLAIMS:

1. A system for tracking one or more objects comprising:

(a) One or more tags transmitting a signal, each tag being configured to be attached to an object to be tracked;

(b) Two or more antenna modules receiving signals transmitted by the tags; and

(c) A processor configured, for each of one or more tags, to: i calculate from signals received by the antenna modules a current location of the tag; and ii compare the current location of the tag with one or more previously calculated locations of the tag and. to determine a status of the tag on the basis of the comparison.

2. The system according to Claim 1 wherein the step of calculating a location of a tag involves calculating a distance of the tag from two or more antenna modules.

3. The system according to Claim 2 wherein each tag periodically transmits a signal and a distance between a tag and an antenna module is calculated based upon an intensity of the signal received by the antenna module.

4. The system according to Claim 2 wherein the antenna modules transmit, in succession, an interrogator signal, and each tag receiving the interrogator signal modulates a tag specific UID code onto the signal and transmits a frequency-shifted signal. ^■■

5. The system according tα Claim 4 wherein a distance between a tag and an antenna module is calculated based upon a transit time from transmission of the interrogator signal by the antenna module to receipt of the frequency- shifted signal at the antenna module.

6. The system according to any one of Claims 2 to 5 wherein a location of a tag is calculated from a distance between the tag and three or more antenna modules by a triangulation technique.

7. The system according to any one of the previous claims wherein the step of comparing the current location of the tag with one or more previously calculated locations of the tag comprises determining a current motion of the tag. 8. The system according to Claim 7 wherein the status of a tag is determined based upon the current motion of the tag. 9. The system according to Claim 8 wherein the status of a tag is selected from the group comprising;

(a) the tag is stationary;

(b) the tag is moving in a predetermined space;

(c) the tag is moving outside a predetermined space; 10. The system according to any one of the previous claims further comprising an alarm.

11. The system according to Claim 10 wherein the processor is configured to sound the alarm when a tag has any one of one or more predetermined statuses.

12. The system according to any one of the previous claims further comprising a display screen.

13. The system according to Claim 12 wherein the processor is further configured to display on the display screen the status of one or more of the tags.

14. The system according to any one of the previous claims disposed at a site including in a defined three dimensional space.

15. The system according to Claim 14 wherein the defined space is a room within a building, two or more rooms within a building, or two or more rooms in different buildings.

16. The system according to Claim 14 or 15 wherein one or more of the antenna modules provide complete coverage of the defined space.

17. The system according to Claim 16 further wherein one or more antenna modules provide coverage outside the defined space.

18. A method for tracking one or more objects comprising: (a) attaching to each of the objects a tag transmitting a signal,

(b) receiving signals transmitted by the tags; and

19. The method according to Claim 18 wherein the step of calculating a location of a tag involves calculating a distance of the tag from two or more antenna modules.

20. The method according to Claim 19 wherein each tag periodically transmits a signal and a distance between a. tag and an antenna* module is calculated based upon an intensity of the signal received by the antenna module.

21. The method according to Claim 19 wherein the antenna modules transmit, in succession, an interrogator signal, and each tag receiving the interrogator signal modulates a tag specific UID code onto the signal and transmits a frequency-shifted signal.

22. The method according to Claitn 21 wherein a distance between a tag and an antenna module is calculated based upon a transit time from transmission of the interrogator signal by the antenna module to receipt of the frequency- shifted signal at the antenna module.

23. The method according to any one of Claims 19 to 22 wherein a location of a tag is calculated from a distance between the tag and three or more antenna modules by a triangulatioη technique.

24. The method according to*^, any one of Claims 18 to 23 wherein the step of comparing the current location of the tag with one or more previously calculated locations of tile tag comprises determining a current motion of the tag.

25. The method according to Claim 24 wherein the status of a tag is determined based upon the current motion of the tag.

26. The method according to Claim 25 wherein the status of a tag is selected from the group comprising;

(a) the tag is stationary;

(b) the tag is moving in a predetermined space; (c) the tag is moving outside a predetermined space;

27. The method according to Claim 26 wherein the predetermined space is a room within a building, two or more rooms within a building, or two or more rooms in different buildings.

28. The method according to any one of Claims 18 to 27 further comprising sounding an alarm when a tag has any one of one or more predetermined statuses.

29. The method according to any one of Claims 18 to 28 further configured comprising displaying on a display screen the status of one or more of the tags.

30. A program storage device readable by^' machine, tangibly embodying a program of instructions execiitable by the machine to perform method steps for tracking one or more objects, each object being attached to a tag transmitting a signal, comprising, for each of one or more of the tags,: calculating, from signals received from the tag, a current location of the tag; comparing the current location of the tag with one or more previously calculated locations of the tag; and determining a status of the tag on the basis of the comparison.

31. A computer program product comprising a computer useable medium having computer readable program code embodied therein for tracking one or more objects, each object being .attached to a tag transmitting a signal, the computer program product comprising: computer readable program code for causing the computer, for each of one or more of the tags,- to calculate from signals received from the tag, a current location of the tag; computer readable program code for causing the computer to compare the current location of the tag with one or more previously calculated locations of the tag; and computer readable program code for causing the computer to determine a status of the tag on the basis of the comparison.