Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2001-03-27
2004-11-02
Tweel, John (Department: 2636)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S505000, C340S572400
Reexamination Certificate
active
06812839
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to object locating and tracking systems, including those of the type described in U.S. Patent to Belcher et al, U.S. Pat. Nos. 5,920,287, and 5,995,046, assigned to the assignee of the present application and the disclosures of which are incorporated herein, and is particularly directed to the generation of a rotating AC magnetic field that effectively maximizes magnetic field coupling with the magnetic field sensor of an RF burst-transmitting tag that comes within a prescribed proximity of a (tag-programming) magnetic field generator.
BACKGROUND OF THE INVENTION
The general architecture of the radio tagged object location systems described in the above-referenced '287 and '046 Patents is diagrammatically shown in
FIG. 1
as comprising a plurality of tag emission readers
10
geographically distributed within and/or around an asset management environment
12
. This environment contains a plurality of objects/assets
14
, whose locations are to be monitored on a continuous basis and reported to an asset management database
20
, which is accessible by way of a computer workstation or personal computer
26
. Each of the tag emission readers
10
monitors the asset management environment for RF emissions from one or more RF-transmitter-containing tags
16
that are affixed to the objects
14
. Each tag's transmitter is configured to repeatedly transmit or ‘blink’ a very short duration, wideband (spread spectrum) pulse of RF energy, that is encoded with the identification of the object and other information that may be stored in a tag memory.
These blinks or bursts of RF energy emitted by the tags are monitored by the readers
10
, which are installed at fixed, and relatively unobtrusive locations within and/or around the perimeter of the environment being monitored, such as doorway jams, ceiling support structures, and the like. The output of each tag reader
10
is coupled to an associated reader processor. The reader processor correlates the spread spectrum RF signals received from a tag with a set of spread spectrum reference signal patterns, to determine which spread spectrum signals received by the reader is a first-to-arrive RF spread spectrum signal burst transmitted from the tag.
The first-to-arrive signals extracted by the reader output processors are forwarded to an object location processor within the processing subsystem
24
. Using time-of-arrival differentiation of the detected first-to-arrive transmissions, the object location processor executes a prescribed multilateration algorithm to locate (within a prescribed spatial resolution (e.g., on the order of ten feet) the tagged object of interest.
In their normal mode of use, the tags exhibit a prescribed operational functionality, such as transmitting or ‘blinking’ an RF signal at a relatively slow repetition rate. The use of a relatively slow blink rate is due to the fact that most of the objects being tracked do not move frequently. However, there may be occasions where it is desired to change the operation of or otherwise communicate information to a tag, such as stopping the tag from blinking or causing it to start blinking, or to transmit additional data, such as that acquired from optional sensors or a data bus.
As another illustration, there are times when the objects to which the tags are attached are moved and may pass through one or more regions of the monitored environment where communications with the tags are desired. For example, the monitored environment may contain ‘increased sensitivity’ regions (such as doorways and the like) where more frequent tag transmissions are desired, in order to ensure that any objects passing therethrough will be readily tracked. One way to accomplish this particular task would be to simply program the tags to blink more frequently on a continuous basis. However, this approach is not acceptable for two reasons. First, more frequent tag transmissions on a continuous basis will shorten the battery life of the tag; secondly it would increase spectrum congestion.
In accordance with the invention disclosed in the above-identified '290 and '079 applications, the above-described tag-reprogramming function is readily achieved by placing an arrangement of one or more relatively short range, modulated magnetic field proximity-based, tag-programming generators or ‘pingers’ at a respective location of the monitored environment that is proximate to a region (such as a doorway) through which a tag may pass. This tag-programming pinger arrangement is operative to emit a non-propagating, AC magnetic field, that is sensed by the tag and used to controllably prompt (or program) the tag to take some action. As a non-limiting example, the tag reprogramming field may be used to cause the tag to immediately begin blinking at an increased rate for a relatively brief period of time, so as to alert the tag-tracking system of the presence of the tag in the region of interest.
Pursuant to the tag-programming scheme disclosed in the '290 application, the magnetic field is modulated or encoded with frequency shift keyed (FSK) encoding signals representative of digital data to be transmitted to the tag, using an FSK-encoded magnetic field based communication scheme of the type detailed in each of the '290 and '340 applications. The use of an FSK-encoded AC magnetic field using operational frequencies typically less than a few hundred KHz allows a large amount of data to be rapidly communicated to the tag.
An alternative approach is detailed in the '079 application, which has particular utility in an environment (such as an industrial facility), where such frequencies may be dominated by man-made and natural noise levels that limit performance, and where the function to be carried out may be relatively simple. In this alternative scheme, rather than use an FSK-encoded magnetic field communication link to transmit ‘data’ (where a fairly large (data) bandwidth may be required and increases susceptibility to interference), the programming magnetic field communication link employs a single frequency or is unmodulated. An example of such a simple function includes proximity detection or transmitting a relatively simple command, which considerably reduces the bandwidth requirement, and allows a reduced complexity communication implementation.
Irrespective of the type of AC magnetic field generation approach employed (modulated or nonmodulated), what is essential to successful operation of the magnetic field communication system is the absence of ‘orientation nulls’ in the magnetic field coverage for the ‘increased sensitivity’ region (such as a doorway and the like), so as to effectively guarantee than any tag entering that region will be fully operationally magnetically coupled with the generated field. These orientation nulls result from misalignment of the magnetic field transmit and receiver coil axes. Indeed, turning the axis of either coil orthogonal to that of peak performance can result in zero-coupling (an orientation null).
A reasonably acceptable resistance to this orientation null effect when the receiver coil lies in a given or fixed orientation can be achieved by sequentially shifting the vector orientation of the transmit field generator over three orthogonal axes. If the magnetic field receive system is comprised of two independent coils operating in such ‘polarization diversity’ (for example, the two receive coils are mutually orthogonal), the coupling performance is essentially coil orientation independent.
Previous attempts to solve the orientation null problem have involved sequentially generating a set of magnetic fields having three respectively different orientations. Unfortunately, this causes a substantial reduction in the rate at which information can be transmitted, since the same data must be repeated three times (one for each orientation).
SUMMARY OF THE INVENTION
In accordance with the present invention, the desire to effectively eliminate such an orientation null is su
Belcher Donald K.
Hash Ronald J.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Tweel John
Wherenet Corp
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