Communications: directive radio wave systems and devices (e.g. – Presence detection only – By motion detection
Reexamination Certificate
2001-01-26
2004-08-31
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Presence detection only
By motion detection
C342S027000, C342S118000, C342S127000, C342S147000, C342S156000, C342S195000, C342S424000, C342S442000
Reexamination Certificate
active
06784826
ABSTRACT:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
None.
FIELD OF THE INVENTION
The present invention relates to the field of motion analysis. More particularly, the invention pertains to clinical research and health care for persons with disabilities, athletes and athletic coaches, and the sports and entertainment industries.
BACKGROUND OF THE INVENTION
Motion study has been of interest for a great many years, particularly that relating to the human body. Sequential pictures of body movement was a subject of early photography. In the early 1970′s a system for quantizing human locomotion, was developed, and methods of joint motion measurement since then. Several types of measuring techniques are now being used: electromechanical linkage; stereometric; accelerometeric; magnetic coupling; biplanar roentgenographic; and radio frequency (RF). Most of these methods are expensive to install and maintain, may be sensitive to interference by body parts, take time to get results and present difficulties in reducing and interpreting the data. The Roentgenographic method, though accurate, presents the hazard of ionizing radiation which is harmful to living subjects.
RF methods have been seriously investigated as an alternative since about 1994. These methods are relatively inexpensive, offer real-time motion capture capability, have high sampling rates, very good resolution and accuracy. The Lawrence-Livermore National Laboratory (Laboratory) and San Diego Children's Hospital and Health Center (CHHC) together developed RF concepts in 1994. At the same time, Softimage of Montreal, Canada was interested in respect of video games.
Over twelve million people in the United States have lower extremity disabilities, according to the U.S. Dept. of Health and Human Services (1994). Five-hundred thousand Americans have cerebral palsy, growing at the rate of 4,500 cases per year. Clinical gait analysis is a diagnostic tool for prescribing treatment for patients who suffer with neuromuscular, musculoskeletal, or neurological impairments. The primary goal in treating a person who has these problems is to correct their functional deficiencies and thereby improve their quality of life. Functional deficiencies are quantified analytically by having the subject perform simple tasks while patterns of limb movements are systematically measured. Motion-capture data reduces the number of surgeries required to correct some problems.
Trakus, Inc. of Medford, Mass., in their Internet site http://www.Trakus.com, describe an RF system which converts object motion into digital data that can be analyzed or used for entertainment purposes. Their product, designed for hockey and football, provides information about an athlete's movements on the playing field. Each athlete wears a transmitter which weighs two ounces. The transmitters send signals to antennas that surround the playing field. The system operates in spread spectrum because of the presence of other RF signals at base frequency of 2.45 GHz. The system uses time of arrival (TOA) measurements to calculate a player's position on the field. Sample rate of these measurements is about 30 times per second for each player on the field.
Providing a method and apparatus for real-time measurement of human body motion has been a continuing problem for clinical researchers, athletic coaches and live-sports commentators, to name a few. There is a great emphasis on knowing the outcome of medical treatment and extraordinary interest in using such motion information to enhance competitive athletics and to complement sports, industry, the military and entertainment. The inability of currently-used technology, to provide inexpensive, real-time analysis of the motion of limbs and joints has been frustrating. This is particularly true of widely used optical systems. Relatively new radio frequency approaches have not yet been applied to the detailed measurements required for the applications mentioned above. Producing analytical measurement of human motion, at a high sampling rate and with high resolution will revolutionize the field of human performance analysis, among other things, by expanding the range of application and reducing the cost of necessary healthcare for disabled persons. Solving these problems would constitute a major technological advance and would satisfy a long felt need in medicine, athletics, and recreation and entertainment industries.
SUMMARY OF THE INVENTION
An objective of the present invention is to develop a precision position measurement system that uses radio frequency (RF) phase interferometry. Energy sources, which are transmitting antennas disposed on a subject, are continuously located by receiving apparatus to a resolution of one millimeter (mm). This data is used, for example, in clinical gait analysis applications. Advantages include significant time savings for data analysis, real-time motion acquisition and display, high frame-rate acquisition, full body motion acquisition and reduced data loss from occlusion of markers on the subject. Enhancement of human body motion performance is an end result. Two methods of measuring position are contemplated.
The first measurement method uses a single antenna at each of several widely separated receiving locations to “triangulate” each energy source. By examining the differences in signal phase at pairs of receiving locations, source position is determined by one of two approaches. A first approach uses a known starting position for a source and computes changes in position. A second approach computes position by examining the enclosed volume for physical positions where the measured phase relationship would occur.
The second measurement method uses a small array of antennas at each of several receiving locations. Each array is able to determine the direction of arrival of the transmitted signal and the transmitter location is determined from the intersection of the direction-of-arrival vectors.
While the discussion which follows focuses on human body motion as an example, the measurement techniques of this invention can also be applied to animals, robotics, mechanical metrology and other articulated bodies and machines.
The Body Motion Tracking System measures path lengths to a number of receiving antennas from a source or “marker” antenna, disposed on a subject at a physical location to be tracked, to provide an estimate of the source's position time history.
Four to six receiving antennas are positioned at the edges of a volume in which activity is being conducted. Each antenna is coupled to a preamplifier which drives a mixer. In a preferred embodiment, the received signal is down-converted to translate the RF energy from microwave frequency to an intermediate frequency (IF) of about three Megahertz (MHz). A single reference oscillator must be fed to all of the mixers in order to preserve the phase relationships of the RF signals from the receiving antennas. The IF signals are presented to a bank of analog-to-digital converters which transform the analog signals to a digital signal format. A common sampling clock, operating in one embodiment at sixteen MHz, is used in this conversion process. Choice of clock frequency depends on the hardware selected and whether direct or sub-sampling is desired. The use of a common clock is required to preserve the phase relationships of the RF signals received.
Digital representations of the received signals are presented to the inputs of a multi-channel digital tuner. The digital signals are translated again to about one KHz. Narrow-band filtering and sampling rate reduction are applied. Phase relationships are still preserved because all of the signal processing up to this step is “coherent.”
The digital data is fed to a main computer and processed to estimate each marker antenna's position. There are significant differences between this technique and conventional direction finding techniques.
Conventional DF systems consist of a number of small arrays of receiving antennas. They operate with the assumption that the range from a source
Kane Ronald J.
Spain, Jr. David Stevenson
Giaccherini Thomas N.
Gregory Bernarr E.
Tera Research Incorporated
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