Wireless item location monitoring system and method

A wireless electronic tracking system employs transmitters attached to moveable target items that send continuous analog radio frequency (RF) digitally-coded signals at prime number differentiated time intervals to a base receiver. The coded signals carry transmitter and base unit identifiers, low battery and attachment status information. The base unit periodically scans using an omnidirectional antenna to determine distance and azimuth for multiple active transmitters, alerting an operator to any status alerts, such as ‘out of range’ status determined by signal strength. The operator can switch to a higher gain, directional antenna to search for an errant target transmitter, or simply to check on the whereabouts of any given target item. Because the movable target items need only transmit, the transmitters can be physically diminutive and unobtrusive to the target wearer, making the system practical for tracking people (e.g. geriatric or juvenile, for assistance or to deter leaving group members behind), animals (e.g. pets, livestock) and even inventory (e.g. especially expensive items that shouldn't move from a given spot in a retail setting).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to wireless monitoring systems and particularly to such systems adapted to monitor the location of movable items such as people, animals or merchandise. More particularly, this invention relates to a wireless transmitter attached to each item and a base station monitoring multiple items, providing out of range alarms and doubling as a finding device.

2. Description of Related Art

Geriatric patients often move about freely within the boundaries of a resident hospital, but some could endanger themselves and become lost and unable to find their way home if they wander outside the grounds. Likewise, pets straying too far from a home location sometimes get lost or stolen. Expensive retail merchandise susceptible to shoplifting can be spirited away and if small enough hidden in the thief's pocket or packages, thereby deterring thorough investigation based on suspicion alone. Horror stories abound of children or scuba divers on tours being left behind because an improper head count overlooked their absence.

Numerous prior art devices and systems provide means for monitoring the location and status of movable items, but most are too expensive and complex for practical use in many of the above circumstances. Systems designed for patients potentially needing immediate medical attention provide a base station and portable transceivers which trigger an alarm, either manually by a distressed patient or automatically by a sensor monitoring body functions such as breathing or pulse. The base unit then alerts help on the premises or contacts emergency response services such as police or paramedics to come to the patient's assistance. Such systems typically involve patient signaling options and transceiver functions in the patient-worn device and in the base unit, making them complex and expensive and reducing the applications in which they are practical.

Other less expensive perimeter monitoring systems rely on passive unit-carried devices which set off an alarm as the unit passes a perimeter sensor, like retail shoplifting detection systems, but which provide no distance and direction capabilities for finding missing units. A simple system which detects unit movement beyond a given perimeter or distance could find wide uses in diverse markets.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide means of tracking continuous care patients who remain ambulatory but may need immediate attention at any given time.

It is another object of this invention to provide means for tracking pets or livestock which may move about but should not leave a premises.

It is another object of this invention to provide economical means for monitoring the exact location of merchandise in a warehouse, retail or other setting.

It is another object of this invention to provide economical means for assuring head count in groups to avoid inadvertent omission of members when the group leaves.

It is yet another object of this invention to provide a diminutive transmitter unobtrusive to the wearer which can be tracked by a base unit.

The foregoing and other objects of this invention are achieved by providing a wireless electronic tracking system which employs transmitters attached to moveable target items that send continuous analog radio frequency (RE) digitally-coded signals at prime number differentiated time intervals to a base receiver. The coded signals carry transmitter and base unit identifiers, low battery and attachment status information. The base unit periodically scans using an omnidirectional antenna to determine distance and azimuth for multiple active transmitters, alerting an operator to any status alerts, such as ‘out of range’ status determined by signal strength. The operator can switch to a higher gain, directional antenna to search for an errant target transmitter, or simply to check on the whereabouts of any given target item. Because the movable target items need only transmit, the transmitters can be physically diminutive and unobtrusive to the target wearer, making the system practical for tracking people (e.g. geriatric or juvenile, for assistance or to deter leaving group members behind), animals (e.g. pets, livestock) and even inventory (e.g. especially expensive items that shouldn't move from a given spot in a retail setting).

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference now to the figures, and in particular toFIGS. 1-2, a general scheme of the present invention depicts multiple targets1being tracked by a single monitoring base unit40according to the present invention. The present invention has a wide variety of applications, some of which are depicted inFIG. 1, such as keeping track of ambulatory patients3at a nursing home or hospital, tracing livestock or pets5within a neighborhood (not shown), or tagging expensive merchandise7to assure it does not leave a retail premises without being purchased. One having ordinary skill in the art will recognize that other targets1may be monitored, with appropriate variations as described below, without departing from the spirit and scope of the present invention.

Transmitter10typically employs attachment means11appropriate to target1. For example, as depicted inFIG. 2, transmitter10includes an elastic strap11forming a loop adapted to surround the arm for comfortable wear by patient3. Alternately, transmitter10could be integrated with the ubiquitous hospital bracelets4commonly worn by patient3in a hospital, nursing home or hospice. For livestock or pets5, transmitter10could be coupled to their collars6, ear tags (not shown), other identifying apparel (not shown) or even embedded into their skin (not shown). For expensive merchandise, transmitter10may comprise a small tag8attached by tether9or could be included in the clothing alarm tags (not shown) attached with magnetically locked pins that pierce the merchandise used in apparel retailing. One having ordinary skill in the art will recognize that all manner of attachment means are contemplated by the present invention, with concomitant variations in form dictated by the circumstances.

In the theft prevention application, unobtrusiveness is a desirable trait. InFIG. 2, transmitter10is depicted enclosed within a substantially rectangular box or case18, but case18could be reduced considerably in size. Components discussed below require only that case18be approximately 1⅛ inches in diameter and ⅛ inch high, making it resemble a wristwatch. In fact, a preferred case18would resemble a wristwatch and strap11would resemble a watch band if transmitter10were to be worn by a patient. One having ordinary skill in the art will recognize that all such variations in case18adapted to contain the components of transmitter10are considered within the spirit and scope of the present invention.

Base unit40comprises housing49having front face48bearing user interface devices such as control switches42,45,46and LCD41providing a readout of selected information about transmitters10. Preferably, base unit40is a hand-held, portable device that normally sits in a central location within the area in which targets1are expected to remain, but which can move with the operator as he attempts to locate a given target1because base unit40detected an out-of-range condition for that target1's transmitter10. One having ordinary skill in the art will recognize that these distinct functions (monitoring all transmitters10and searching for an errant target1) may be embodied in separate devices. For example, the monitoring function could be embodied in a stationary base station (not shown) while a portable base unit40could duplicate its search and detection functions while being useful to accompany the operator on a mobile search for target1. Both functions, however, can be embodied within a single base unit40which can be operated to select between these functions, as discussed below.

Referring now also toFIGS. 5A-5Band6A-6E, transmitter10comprises microcontroller13adapted to generate five byte word20(FIG. 3) and transmit it at millisecond intervals defined by prime numbers selected from a plurality of prime number intervals according to Chart A. Each transmitter10may be set to transmit at a single prime number interval to reduce interference from other transmitters10. SeeFIG. 6D. Each transmitter10thus remains detectable by base unit40and distinguishable from other transmitters10and from background noise despite the fact that numerous transmitters10are within the scanning area of base unit40. Base unit40preferably is capable of tracking at least sixty (60) transmitters10transmitting at prime number intervals up to approximately 500 milliseconds before the practical upper limit of prime number interval transmissions is reached.

As depicted inFIGS. 5A,5B, transmitter10further comprises microcontroller/transmitter13, battery pack12, RF generator14and transmitter antenna16. A suitable transmitter microcontroller13is RFPIC12F675H-ISS available from Microchip Technology, Inc. of Chandler, Ariz. A suitable battery12is a single coin cell or two (2) quadruple ‘A’ (2-AAAA) batteries commonly available commercially. Transmitter antenna16preferably comprises a quarter (¼) wave loop antenna wrapped around the inside of case18, but transmitter antenna16alternately may serve a dual purpose, as discussed below.

Preferably, transmitter10transmits to base unit40at 915 megahertz (MHz), the frequency commonly used by cellular telephones and pagers. Alternately, transmitter10may utilize the 433.9 MHz band used in Europe for such devices. One having ordinary skill in the art will recognize that transmitter10could operate at any frequency without departing from the spirit and scope of the present invention. For the preferred 915 MHz band, transmitter antenna16would comprise a quarter wave loop of approximately three (3″) inches in length.

Transmitter10preferably generates a one (1 mW) milliwatt RF signal capable of being detected by base unit40using its omnidirectional antenna51(FIG. 7B) as long as transmitter10remains within a short distance of base unit40, preferably up to approximately 250 feet. As discussed in detail below, base unit40further is capable of detecting the same signal with its directional antenna as long as it remains within a distance of approximately 450 feet. One having ordinary skill in the art will recognize that the foregoing physical distance limitations are artifacts of the components selected and the purpose to which the present invention is applied, and that all variations thereon are considered to be within the spirit and scope of the present invention. For example, transmitter10further included potentiometer17(FIGS. 5A. 5B) which may be employed to set the power output fed to transmitter antenna16, thereby providing means for reducing the distance transmitter10may be detected by base unit40. This enables operators of a system employing the present invention to increase or decrease the apparent radius within which targets1must remain to avoid triggering an out-of-range condition and alarm within base unit40.

As best seen inFIGS. 5A,5B, transmitter microcontroller13is powered by battery12, providing approximately three (3 vdc) volts direct current input to pin VCC of transmitter controller13. Low battery signal58is tied to pin3of transmitter controller13, which allows controller13to monitor battery12. When VCC drops as battery12begins to run low, the voltage value at signal58drops correspondingly. Transmitter controller13can be set to detect a low battery condition from signal58long before battery12drops below the minimum VCC at which controller13can operate. Controller13then sets a bit within word20, as discussed in more detail below, to trigger an alarm at base unit40that the battery needs to be replaced well before transmitter10ceases to operate.

FIG. 5Aalso illustrates another valuable feature of the present invention whereby transmitter10sounds an alarm to base unit40if transmitter10has been removed from target1. As depicted inFIG. 2, a disconnect loop56may be embedded within strap11or otherwise deployed to surround a portion of target1, such as the wrist of the patient wearing hospital band4or the neck of the animal wearing collar6. Loop56comprises a material of considerable mechanical strength and sized such that it cannot be removed from target1without being disconnected. Loop56also comprises an electrical conductor coupled to an input of transmitter controller13and looped back to ground57(SeeFIG. 5Awhere loop56is represented by a box electrically coupled to pin17of controller13and grounded at grounding connection57. This provides affirmative logic to transmitter13confirming that loop56remains in tact, thus implying that transmitter10remains attached to target1. If loop56becomes disconnected or broken, ground57no longer couples to pin17and cannot confirm to controller13that transmitter10is attached to target1. Controller13is programmed thereupon to set a bit within word20, as discussed in more detail below, that triggers an alarm in base unit40.

In an alternate embodiment of the foregoing, as illustrated inFIG. 5B, transmitter antenna16itself provides the function of loop56. In such case, where transmitter antenna16becomes decoupled from antenna ground57(FIG. 5B), transmitter10would cease transmitting, setting off an out-of-range alarm at base unit40and drawing the attention of an operator just as effectively as would the breaking of loop56, as discussed above. Where transmitter antenna16is used in this fashion, it may be necessary to lengthen transmitter antenna16sufficiently that it can surround a portion of target1, such as the wearer's wrist or neck (FIG. 1). In such case, transmitter antenna16may have to be a half-wave or full-wave loop instead of the preferred quarter-wave loop discussed above. For the preferred transmitter frequency discussed above, transmitter antenna16thus would become six (6″) inches (half-wave loop) or twelve (12″) inches (full wave loop). One having ordinary skill in the art will recognize that all such variations come within the spirit and scope of the present invention.

Turning now again toFIG. 3, signal word20generated by transmitter10carries several distinct pieces of information using an alpha-numeric code of known convention, such as ASCII, about transmitter10to base unit40. Preferably, bytes21-23carry identifier and status information about transmitter10, including to which base unit40it transmits. Fourth byte24provides error detection and correction for word20using checksum convention, thus assuring that word20is not corrupted by background noise or other random error. Byte25provides a distance measurement, as discussed in detail below.

Within byte22, the first two bits (bits0and1) preferably are flag bits which signify to base unit40that disconnect loop56(or alternately transmitter antenna16) is grounded and that controller13is not detecting a low battery condition, as discussed above. Bits2through7preferably signify a unique identifier for transmitter10, essentially a binary number. Using seven bits in byte22word20can carry a unique numeric identifier for up to sixty-three (63) different transmitters10. When base unit40monitors a selected prime number interval signal and happens to detect more than one word20being transmitted at that interval, base unit40can distinguish between them based on the transmitter10and base unit40identifiers in word20and select the correct signal to monitor, ignoring the other(s).

If transmitter10happens to be detected by more than one base unit40, word20carries in bytes23,24ASCII character identifiers, e.g. “G” and “O”, each having a corresponding ASCII numeric value, that signify a particular base unit40to which transmitter10is transmitting. This allows the appropriate base unit40to identify its target1and to disregard a target1it is not set to monitor. This could occur, for example, when two base units are operating in a single area where their monitoring ranges overlap, or where they are monitoring different types of targets1. Other base units40can be assigned other character identifiers. Using two bytes23,24creates the possibility of having as many as 255×255 base units40operating in the same area, though this is highly unlikely to occur. Using two bytes23,24, however, allows for the possibility that two different base units40may intentionally monitor the same target1for different reasons, if base units40and transmitters10are so programmed. This could occur, for example, if the base units40were monitoring proximity to different boundaries, such as where there was an off limits area (e.g. an unsafe zone) within a larger area of confinement.

Fifth byte25of word20provides base unit40a basis for determining signal strength, which base unit40utilizes to determine direction and distance from base unit40to transmitter10. Specifically, byte25is set to a high value (ASCII value 255, or all 1's in an 8-bit byte), thus creating the maximum analog signal for byte25. As base unit40samples the analog signal emanating from transmitter10, it detects an analog signal strength even though bytes21-25are digitally valued to provide digital information to microcontroller60of base unit40. Thus, if analyzed digitally, bytes21-24could comprise an analog value of anywhere from zero to 255 (i.e. some combination of 0's and 1's in an 8-bit byte, thus totaling less than 255) for each byte21-24. By setting byte25always to all 1's (ASCII value 255), the analog signal thereof always is set at a maximum. By sampling the signal at 26 millivolts per decibel (dB) and calculating the analog value as a percent of the maximum signal strength, where if transmitter10is adjacent base unit40, microcontroller60can estimate the distance to transmitter10from base unit40.

Referring again toFIG. 1and also turning now toFIGS. 7A,7B, base unit40further comprises antenna system means50for receiving signals from transmitters10, receiver70for detecting signals coming through antennas50and microcontroller60for analyzing detected signals and integrating transmitter10database information for detected transmitters10with the user interface. Receiver70couples between antenna system50and controller60to provide analog-to-digital conversion of the signal so that coded signal word20from transmitter10may be analyzed by controller60, as discussed in more detail below.

Antenna system50comprises omnidirectional antenna51and directional antenna55, each selectable for different functions of base unit40. Both antennas51,55are contained within or built onto housing49and coupled to controller60through receiver70(FIG. 8A). Switch53on face48provides an operator with the capability to manually select between antennas51,55depending upon the function being performed. Preferably, directional antenna55is a Yagi type reflector/director dipole antenna etched onto a circuit board (not shown) integral with base unit40. A suitable antenna system is described in U.S. Pat. No. 6,307,525 to Britain.

Processor60is programed for several functions. First, it receives from transmitters10coded signals in the form of word20and analyzes them as discussed above to provide updated status and identifying information to the operator (FIG. 8C). Processor60also integrates with a user interface disposed on face48of housing49and provides the operator with controls for responding to an alarm condition and for searching for the errant transmitter10.FIGS. 8D-8Udemonstrate the various routines carried out by processor60to parse information from user interface input buttons42,45,46and53(FIG. 1) for selecting which function to perform, and for analyzing coded signals from transmitters10.

Controller60also maintains a database (not shown) of transmitters10assigned to base unit40. Such database is designed to store in a record for each transmitter10its identifier number, status (active or inactive), the latest calculated direction and distance of transmitter10based on the last known detection of word20from transmitter10, and, if so designed, additional data, such as information about target1. Controller60can retrieve data and information from the database and display it with LCD41for the operator's inspection at any time. An operator thus can select one or more transmitters10to listen for specifically, should some other clue, such as a shout or other off-system alarm, indicate attention needs to be directed thereto.

For example, if the database is so constructed, specific information about target1could be retrieved by processor60and flashed onto liquid crystal diode (LCD)41in response to an out-of-range alarm, perhaps telling the operator what to look for (e.g. a particular item of merchandise) or whose name to call (should it be a pet or a patient in need of attention). Alternately, the identifier for transmitter10may be displayed for the operator to cross reference with a list identifying the wearer of transmitter10where such information is available. One having ordinary skill in the art will recognize that all such variations are considered within the spirit and scope of the present invention.

In operation, base unit40functions in two modes defined by the antenna it uses to scan for transmitters10. In its normal mode, base unit40listens at the selected prime number intervals for any transmitters10which it considers active. Those transmitters10presumably are within normal distance, and base unit40's omnidirectional antenna51(FIG. 7B) has enough gain to detect them. If an expected word20is not detected within approximately 5.4 seconds, transmitter10is consider out-of-range, triggering an alarm. If word20is detected within the envelope of this sampling cycle, then the out-of-range indication is cleared and operation proceeds as normal.

Should base unit40detect an out-of-range condition, the operator (not shown) of base unit40can switch to directional antenna55using the activate/find button45on base unit40. Having a much greater gain using directional antenna55, base unit40may be able to detect the errant transmitter10in time for the operator to bring assistance or find target1before disaster befalls, such as target1being spirited away by malevolent actors (not shown).

When an alarm signals an out-of-range condition for an active transmitter10, preferably an audible alarm sounds to alert an operator. The operator then initiates an acknowledge routine (FIG. 8L) by depressing switch45(FIGS. 1,4C,8B,8C) to notify controller60that he is aware of the alarm and wants information contained within controller60's database about target1to which the out-of-range transmitter10is attached. Controller60then interrogates the database and displays the target1information (FIGS. 8K,8L,8N,8S). Next, the operator may initiate a search routine (FIGS. 4B,8I) by depressing activate/find button46to find transmitter10.

To carry out a search, the operator can verify the alarm by selecting transmitter10for azimuth and distance determination (FIG. 4B). Specifically, the operator switches from omnidirectional antenna51on base unit40to directional antenna55, thereby amplifying the gain for signal strength detection. LCD41switches to a bar graph indicating signal strength calculated from byte25as discussed above. Should transmitter10remain within the larger range detectable with directional antenna55, the operator then can rotate base unit40in a horizontal plane through 360 degrees to determine the azimuth at which signal strength is maximized. This then indicates the direction to transmitter10, while the overall signal strength indicated by LCD41, as a percentage of maximum, indicates distance. Many times, this may be all that is necessary to identify visually target1bearing transmitter10and allow the operator to proceed in visual mode, perhaps calling out to target1(e.g. a person or pet) or tracking down target1hidden within clothing or other materials (e.g. merchandise in the process of being stolen).

The present invention, described in either its preferred or alternate embodiment, thus provides means for monitoring a plurality of targets1by attaching to them relatively inexpensive transmitter10and monitoring them by similarly economical base unit40. Tour operators can issue transmitters to every member of a group and check to assure that all are on board a bus or boat prior to leaving the immediate area. Base unit40can be programmed to provide a head count and to compare that to the expected head count, sounding an alarm if they are not the same, and further identifying the transmitters not reporting.

While the invention has been particularly shown and described with reference to one or more embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. For example, specific hardware has been described for providing base unit40capable of monitoring a finite number of transmitters10limited by the prime number intervals of Chart A, but other equipment could increase or decrease the practical population of transmitters10.