Communications: electrical – Selective – Interrogation response
Reexamination Certificate
2000-05-31
2002-02-19
Mullen, Thomas (Department: 2632)
Communications: electrical
Selective
Interrogation response
C340S003510, C340S505000, C340S539230, C340S870030
Reexamination Certificate
active
06348856
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a detection system for determining information concerning the location of objects, and which can be extended to determine movement and orientation and even physical parameters such as shape of objects in a specified environment. The invention can be applied to people and animals as well as inanimate objects such as furniture, machines, vehicles, equipment and the like, and in this connection object is intended to include any movable entity.
BACKGROUND OF THE INVENTION
Location systems are known which allow the presence or absence of an object in a specified environment (such as a room) to be confirmed or denied, and relative to one or more reference points, to identify where in the environment the object is located.
EP 0485879 describes a system for locating vehicles in automatic guidance transport systems.
Ultrasound is employed as a distance measuring medium whilst an infra-red link allows connection between vehicles.
WO 95/14241 describes a tracking system which enables a spotlight to follow a person on a stage carrying a transponder. Again infra-red signals are used to instigate ultrasonic transmissions to determine the position of the transponder and therefore the person. The spotlight is moved accordingly.
EP 0591899 describes another spotlight controlling system for tracking a moving target (actor on stage) carrying a transponder.
Here the radio transmissions establish the communication link and ultrasound transmissions are employed to determine distance and position.
These systems do not allow for the introduction of any new labelled object into the environment being monitored, without operator involvement. Nor do they make and provision for noting if an object ceases to respond due to its movement out of range, or it being screened, nor to any change in the rate of position determination.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a detection system no: only capable of locating the position of labelled objects in a specified environment, and which can be modified to allow orientation, rotational movement and linear movement to be determined and tracked, and allow for control of operable devices on or associated with the labelled objects, but which will automatically respond to the introduction of a new labelled object into the environment and begin measuring its position, orientation, movement etc.
THE INVENTION
In a system embodying the invention in which the position of each of a plurality of labelled objects in a specified environment is determined by determining the transit time of slowly propagating energy transmitted from a transmitter on each labelled object, to a plurality of receivers positioned at fixed points in or around the specified environment, and computing therefrom the actual distance of the transmitter from the receivers, wherein the transmission of the slowly propagating energy is initiated by a burst of high speed propagating energy from a master transmitter located so as to cause transmitted bursts of such high speed energy to enter the said environment, and wherein the transmitter on the object is associated with a receiver adapted to respond to an appropriately encoded burst of such high steed energy, to thereby initiate a burst of slowly propagators energy (each transmitter/receiver combination being referred to as a transponder) a further transmitter of high speed energy is provided on the object, associated with the receiver thereon, to transmit signals, such as data, to a remote receiver using encoded high speed energy transmission.
Preferably each of the said plurality of receivers is adapted also to be responsive to a said burst of high speed energy, so as to identify the beginning of a window of time within which a slow speed energy burst may arise and be received thereby. The burst may be the same burst as is sent to trigger one of the transmitter/receiver units to transmit a slowly propagating wave, for time measurement.
Alternatively the said plurality of receivers may be connected by a network of cables and the reset signals and the polling of the time values may be achieved via the network.
Preferably the receivers include a latch to retain information about the time at which the beginning of a burst of slow speed energy is received after the beginning of each said time window.
Preferably the receivers are scanned (ie polled) so as to recover the time information and reset the latches.
Preferably computing means is provided to associate the time information with the receiver from which the times have been obtained, and generate a transmit time for each receiver.
Preferably the computing means is programmed to convert the transit time into distance values and using position data relating to the receivers stored in a memory, to compute therefrom the position of the object mounted transmitter from each of the receivers, and therefore, by geometry its position relative to one or more fixed points defining the specified environment.
By encoding the high speed energy transmission, so a plurality of different slow speed signal transmitters all located in the same specified environment, can be triggered in turn, so that during a sequence of time windows, position data relating to each of the slow speed signal transmitters in the environment can be obtained, the data in each window relating specifically to one only of the object mounted transmitters.
Typically the slow speed signals are acoustic or ultrasonic signals and the high speed signals are electric currents or voltage or visible or invisible electromagnetic radiation such as IR, UV or radio signals.
Encoding of the high speed signals may be by way of frequency or amplitude or phase modulation or pulse coding or any combination thereof, and preferably digital encoding techniques are employed, if only to ensure adequate signal to noise ratios can be achieved.
Background Theory to Position Determination
Such systems are based on the principle of location by multilateration. For each object that is to be located, the straight-line distances are measured from a point on that object to a number of other points in the environment whose positions (in some frame of reference) are already known. Given enough distances, and a suitable geometry of the endpoints between which they are measured, it is possible to derive a position for the object.
To determine the distances between objects and points in the environment, transmitters and receivers are placed on them and measurements are made of the times of signal pulses being generated and received. The system can be used to measure round trip delays, or alternatively can give the difference in the one-way delays for signal pulses sent simultaneously (or with known time offsets). If the one-way delay in two media are dt
1
and dt
2
, then
D=dt
1
−dt
2
, and
if the (predictable) velocities of propagation in the two media are v
1
and v
2
, and the distance between transmitter and receiver is R, then
R=D/(1/v
1
−1/v
2
).
It may be seen that if v
2
is much greater than v
1
, then the range calculation can be approximated by
R=Dv
1
.
Thus, if, for example, radio and ultrasonic signals are transmitted simultaneously (through space and air as the respective media), then the equation R=Dv
1
is sufficiently accurate for the limited range of an indoor environment, such as a typical house, room, office or even small factory unit or warehouse.
It is not necessary to transmit both fast and slow speed signals simultaneously. A radio pulse for example, can be treated as if its travel time is zero (i.e. independent of range), and it can thus simply be used as a trigger signal. However the flight times of the slow signal pulses (e.g. ultrasonic pulses) can be accurately measured by synchronising the transmitter and receiver units, as by a timing pulse generated by a suitable controller.
Reflections from other objects in the transmitter's environment may cause multiple signals to arrive at a receiver. Any direct-path signal from the tran
Jones Alan Henry
Ward Andrew Martin Robert
AT&T Laboratories - Cambridge Limited
Lee, Mann, Smith McWilliams, Sweeney and Ohlson
Mullen Thomas
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