Alken Inc.

Polhemus, Inc.

Other

Mcdonnell Douglas Corporation

Herbert R Jones

Robert F Higgins

Henry E Himberg

Igor Khalfin

Allan G Rodgers

Plural transmitter coils of a magnetic locating system are driven with widely-separated main frequencies. One of the transmitter coils is also driven with a marker frequency close to the main frequency applied to that coil. The receiver determines a phase relationship with the transmitter based on the main and marker frequencies, so that the receiver does not suffer from phase ambiguity. The main and marker frequencies may interfere with one another, and the receiver may correct for such interference based on known characteristics of the signals at the main and marker frequencies.

AC magnetic tracking system with phase locking

In an AC magnetic tracker one or more multi-axis field sources, each operating at a different frequency, or frequency set, are detected and tracked in three-dimensional space, even when wireless or otherwise not physically connected to the tracking system. Multiple sources can be tracked simultaneously as they each operate with their own unique detectable set of parameters. The invention not only provides the ability to uniquely identify one or more sources by their frequencies, but also to synchronize with these frequencies in order to measure signals that then allow tracking the position and orientation (P&O) of the source(s). Further, these sources need not be present at the time of system start-up but can come and go while being detected, discriminated and tracked. It also should be noted that application of such systems in multiples with more sensors not synchronized to a source or sources also could be employed to give the reverse appearance of a known source phase and incoherency with the sensors.

AC magnetic tracking system with non-coherency between sources and sensors

Techniques for removing distortion in an AC magnetic tracker identify a characteristic frequency in the distortion environment which is then utilized to extract distortion components from the tracker receiver signals so that the corrected position and orientation can be calculated. A multiplicity of alternative techniques for determining this characteristic frequency are disclosed, several of which can be done during operation without interrupting system operation while others can be done off-line. The invention also allows the use of a tuned tracker transmitter since it does not need to operate at multiple frequencies. The invention differs from the prior art by treating an extended conductor characteristic as just another unknown. The position and orientation algorithm solves the 6 unknown coordinates of position and orientation plus the one more unknown&#x2014;the extended conductor characteristic frequency. This enables the tracker to operate full time in one mode of operation without ever suspending normal operation and without additional hardware capabilities.

Magnetic position and orientation measurement system with eddy current distortion compensation

A highway safety net for catching and controlling a vehicle travelling towards the opposite direction of traffic comprises netting connected to a lower cable. A first post top is connected to the netting for supporting the netting. A second post top is connected to the first post top. A first stabilizer bar is connected to the lower cable. The first stabilizer bar is connected adjacent to the first post bottom. A second stabilizer bar is connected to the lower cable. The second stabilizer bar is connected adjacent to the second post bottom.

Highway safety net

A retractable cover for recreational vehicle to provide retractable sunshade comprises a support frame connectable to a recreational vehicle roof. A cover spindle is connected to the support frame. A cover first end is windably connected to the cover spindle. A cover arm is rotatably connected to the support frame. The cover arm is connected to the cover second end. Multiple arched truss arms are rotatably connected to the support frame.

Retractable cover for recreational vehicle

Methods and apparatus for position/orientation tracking within a bounded volume employ at least one stationary sensor, called a &ldquo;witness sensor,&rdquo; having a fixed position and orientation near or within the volume to account for electromagnetic distortion. One or more probe sensors are placed on an object to be tracked within the volume, and the output of each witness sensor is used to compute the parameters of a non-real effective electromagnetic source. The parameters of the effective source are used as inputs to the computation of position and orientation as measured by each probe sensor, as if the object were in the non-distorted electromagnetic field produced by the effective source or sources. In addition to trackers for helmet-mounted displays in aircraft, tank, and armored-vehicle applications, the invention finds utility in any electromagnetic tracking system which might be subject to electromagnetic distortion or interference. Such application areas include electromagnetic motion capture systems, and medical systems and instruments, among others.

Methods and apparatus for electromagnetic position and orientation tracking with distortion compensation

Electromagnetic field mapping is accelerated by acquiring data from the surface bounding a volume of interest and solving the boundary value problem (BVP) using Green's function in a preferred embodiment. Instead of measuring electromagnetic field components on a step-by-step basis at each point within a region of interest, only a component of the field, preferably the normal component, is measured on the surface bounding the volume. The use of surface data acquisition, a solution to the BVP using Green's function, and optional error correction based on the treatment of errors as virtual sources, combine to produce a process of defining of the electromagnetic field within the volume that reduces to a few minutes what presently takes days or longer, and sometimes impossible. Data acquisition may be carried out either by moving sensors along the surface or, preferably, by fixing the position of several single axis or one-directional sensors on the surface bounding the volume without the necessity of moving parts. All geometry-dependent parameters, as determined by the shape and size of the volume of interest, may be pre-computed or computed independently on measurements. In addition to electromagnetic tracking systems, including LOS tracking, the methodology is directly applicable to electromagnetic motion capture systems, tomographic systems and devices (including optical, X-ray, magnetic), non-destructive electromagnetic measurements, and remote sensing.

Method and apparatus for determining electromagnetic field characteristics within a volume

A method and apparatus for determining the position and orientation of a remote object relative to a reference coordinate frame includes a source having a plurality of field-generating elements for generating electromagnetic fields, a drive for applying, to the generator element, signals that generate a plurality of electromagnetic fields that are distinguishable from one another, a remote sensor having a plurality of field-sensing elements for sensing the fields generated by the source, and a processor for processing the outputs of the sensing elements into remote object position and orientation relative to the source reference coordinate frame. The processor compensates the position and orientation values as a function of displacement of either the field-generating elements from a common center, or the field-sensing elements from a common center, or both. Techniques are disclosed for compensating for small-scale non-concentricity in order to overcome imperfections in the orthogonal coil sets wound on a common core, each set defining the source or the sensor. Techniques are also disclosed for compensating for large-scale non-concentricity to allow physical separation of the coil set defining the source or the sensor to dispersed locations that may be more desirable for a particular application.

Non-concentricity compensation in position and orientation measurement

A method and apparatus is provided for determining remote object orientation and position with an electromagnetic coupling. A plurality of radiating antennas are provided for radiating electromagnetic energy. Each of the radiating antennas have independent components for defining a source reference coordinate frame. A transmitter is provided for applying electrical signals to the radiating antennas for generating a plurality of electromagnetic fields. The signals are multiplexed so that the fields are distinguishable from one another. A plurality of receiving antennas are disposed on a remote object for receiving the transmitted electromagnetic fields. The receiving antennas have a plurality of independent components for detecting the transmitted electromagnetic fields and defining a sensor reference coordinate frame. An analyzer is provided for receiving the output of the receiving antennas and converting the components of the transmitted electromagnetic fields into remote object position and orientation relative to the source reference coordinate frame. The analyzing means includes means for processing the components of the electromagnetic fields independently into remote object position in cartesian coordinates and remote object orientation using a quaternion processing strategy. The processing technique provides an uncoupled, noniterative, closed form solution for both position and orientation which is fast and continuous. Further, in the case where dipole antennas are used and the size of the antennas is significant relative to the separation distance between the radiating and receiving antennas, an aperture compensation technique is provided for compensating for distortion in the dipole fields. Still further, the processing technique provides an arrangement for smoothing or filtering the solution for position and orientation by blending previous solutions into the current solution.

Growing community of inventors

Williston, VT, United States of America

Herbert R Jones