System for three dimensional positioning and tracking

Details System for three dimensional positioning and tracking System for three dimensional positioning and tracking

1999-06-30

2001-11-13

Patidar, Jay (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C342S152000, C342S153000, C702S153000

Reexamination Certificate

active

06316934

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally, to positioning systems and more particularly to positioning systems employing alternating electromagnetic fields.
BACKGROUND OF THE INVENTION
Various types of positioning systems which employ alternating electromagnetic fields are known. The following U.S. Patents and foreign patent documents are believed to represent the state of the art:
U.S. Pat. Nos. 4,054,881 and 4,314,251 to Raab; 4,622,644 to Hansen; 4,737,794 to Jones; 4,613,866, 4,945,305 and 4,849,692 to Blood, 4,017,858 and 4,298,874 and 4,742,356 to Kuipers; 5,168,222 to Volsin et al; 5,0170,172 to Weinstein; and 5,453,686 to Anderson; WO 94/04938 to Bladen.
U.S. Pat. No. 4,710,708 to Rorden describes a positioning system which employs only one magnetic coil.
Genetic algorithms are described in
Genetic algorithms in search: optimization and machine learning,
D. Goldberg, 1989; and
An introduction to genetic algorithms,
Melanie Mitchell, 1996.
PLL technology is described in
Phase locked loop: simulation and applications,
by Roland E. Best, McGraw-Hill Book Company, ISBN 0070060517.
The disclosures of all publications mentioned in the specification and of the publications cited therein are hereby incorporated by reference.
SUMMARY OF THE INVENTION
The present invention provides improved apparatus and method for positioning and tracking objects. A block diagram of the disclosed system is shown in
FIG. 1
d.
In accordance with a preferred embodiment of the present invention a system comprises of N transmitters, where N≧6, and at least one probe sensor which detects at least 6 electromagnetic signals, each characterized by its own frequency. The probe sensor typically comprises a single magnetic field detector that is connected to a digital signal processing circuit. The analog output of the magnetic signal detector is a voltage signal proportional to the superposition of the N magnetic field transmitters at the coordinates x
i
, y
i
, z
i
, &thgr;
i
, &phgr;
i
, where the index i denote the position of the magnetic coil i. It is a particular feature of a preferred embodiment of the present invention that the antenna coils need not be exactly mutually orthogonal and certainly need not be arranged such that the centers of the antenna coils coincide.
The analog signal is digitized and is introduced to an integrated digital signal processor block, as an input data. The digitized input data from the of the magnetic detector is then used by the digital signal processor unit to compute the position and orientation coordinates of the magnetic detector. The output from the digital signal processor unit is then transferred to the Data Communication unit and then to the System Control Unit. The refresh rate of the output data is typically of the order of few times per second to a few hundred times per second.
The detector may comprise a one-axis antenna coil, as illustrated in
FIG. 2
, or may alternatively comprise any other suitable type of one-axis magnetic field detector, such as a Hall-effect detector or a solid state component e.g. a magneto-resistive detector or a magneto-diode or a magneto-transistor. The digital signal processor unit typically comprises three modules: a tracking and control module, an envelope detector module and a position determination unit. The tracking and control subsystem is operative to increase the precision of the position determinations by decreasing the dynamic range of the input signal to the A/D converter.
The output of the tracking and control module is supplied to an envelope detector, which is operative to determine the received envelope amplitudes (magnitude and sign) C
1
, . . . , C
N
of the N magnetic signals received from the N RF transmitters. The tracking and control subsystem preferably comprises an Linear Predictive Coding (LPC) module. The envelope detector module typically comprises of N identical envelope detectors (EDs) working in parallel. Optionally, each of the ED modules comprises two sub-modules: a Phase Lock Loop (hereafter PLL), and a System Synchronization Unit, which is called during the operation of the ED module to define the absolute sign of the signal amplitude. Alternatively, each ED module comprises three sub-modules operating in parallel and another sub-module that is called when a system synchronization is needed. The three modules are: a Phase Lock Loop (hereafter PLL), a Non-coherent absolute value envelope-detector, and a Sign Detection Unit. A fourth sub-module, System synchronization unit, is then called to define the absolute sign of the signal amplitude.
The output of the envelope detector is supplied to the position determination unit which is operative, based on the signed amplitude values supplied by the envelope detector, to provide an output indication of the position of the magnetic field detector in the sensor.
The operation of the position determination unit is typically based on solving N analytic equations with 6 unknowns.
A genetic algorithm method is typically employed for solving the position equation to obtain the position and orientation of the detector.
There is thus provided in accordance with a preferred embodiment of the present invention a system for monitoring of the position of at least one portions of an object, the system including a plurality of transmitters operative to transmit alternating magnetic fields within a three-dimensional space, and at least one positioning sensors arranged to be fixed to at least one corresponding portions of the object whose positions it is sought to monitor, each of the at least one positioning sensors including a magnetic field receiver having at least one active axes and operative to receive at least one component, lying along the at least one active axes respectively, of the alternating magnetic fields, and at least one digital signal processors for storing at least one characteristic of the magnetic fields as transmitted by the plurality of transmitters and comparing the at least one characteristic to at least one characteristic of the magnetic fields as received by at least a corresponding one of the at least one positioning sensors and, accordingly, determining and providing an output indication of at least one position characteristic of at least one corresponding portions of the object.
Further in accordance with a preferred embodiment of the present invention the at least one sensors comprise a single sensor arranged to be fixed to a single portion of the object whose position it is sought to monitor.
Still further in accordance with a preferred embodiment of the present invention the at least one position characteristic comprises at least one dimension of the spatial position of the object portion. Preferably the at least one position characteristic also includes at least one dimension of the angular position of the object portion.
Additionally in accordance with a preferred embodiment of the present invention the at least one sensors comprise a plurality of sensors arranged to be fixed to a corresponding plurality of portions of the object whose positions it is sought to monitor.
Moreover in accordance with a preferred embodiment of the present invention the magnetic field receiver has a single (detection) active axis and is operative to receive the component of the alternating magnetic fields lying along the single (detection) active axis.
Preferably the plurality of transmitters are operative to continuously transmit said alternating magnetic fields.
There is also provided in accordance with another preferred embodiment of the present invention a system for monitoring the position of at least one portions of an object in three-dimensional space having three axes, the system including at least six magnetic transmitters each having a center and each operative to transmit alternating magnetic fields within a three-dimensional space, a transmitter orientation maintainer operative to maintain at least three of the transmitters in orientations such that at least a component of the magnetic field of at least one of the

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