Measuring and testing – Speed – velocity – or acceleration
Reexamination Certificate
2000-04-17
2002-04-30
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
C073S167000
Reexamination Certificate
active
06378367
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to speed measuring devices particularly suited for use in determining velocity magnitude or speed of sports objects, and more particularly, to low cost, low energy radar devices for use in measuring the speed of baseballs, baseball bats, paint balls from paint ball guns, and other sports objects, or the speed of movements by martial artists and other players, particularly during training.
BACKGROUND OF THE INVENTION
Continuous wave (CW) Doppler radar technology is commonly utilized to detect a moving object illuminated by the electromagnetic field of the radar and producing an electrical signal at a Doppler frequency which is a measure of the relative speed of the moving object. This technology has been pioneered and developed by the defense industry in the United States, is well documented in textbooks and reports, and has found numerous applications in consumer products. Security motion sensors, industrial position sensors and police radar units are examples of current uses of Doppler radar systems.
Doppler radar has been used in sports applications to measure the velocities of sports objects or players relative to one another or relative to a reference point. Examples of sports radar in use are found in U.S. Pat. No. 4,276.548 to Lutz and U.S. Pat. No. 5,199,705 to Jenkins et al. Conventional sports radar includes “speed guns” for measuring baseball or softball speed, such as disclosed in the Lutz patent. Available sports radar units generally occupy approximately 200 cubic inches and cost several hundred dollars. These units are typically operated by a third person somewhat remote from the thrower and receiver.
Implementation of prior art CW Doppler radar systems is relatively complex, generally involving the use of an RF oscillator and signal generator, an antenna system to radiate the oscillator output into free-space and to receive a portion of the transmitted electromagnetic energy that is reflected by the moving object, a transmit/receive switch, diplexer, or circulator device if a single antenna is used for both transmit and receive rather than separate transmit and receive antennas, and various local oscillators, mixers, phase-locked-loops and other “front-end” circuits to heterodyne, demodulate and detect the Doppler signal. This complexity imposes high cost and size requirements on the radar units, which have heretofore discouraged the utilization of CW Doppler technology in consumer applications where extremely small size and low cost are necessary for practical end product realization.
In electronics applications unrelated to those discussed above, Doppler radar systems using simple homodyne circuits have been known. Such applications include defense applications such as ordnance proximity fuzes and target detectors where Doppler modulation provides evidence of a target encounter. Validation of the presence of target signals within a prescribed Doppler frequency passband and the detection of amplitude build-up as the target encounter distance decreases are sufficient for signal processing and decision making in such systems, obviating the need to accurately measure or calculate the specific velocity magnitude or speed. For example, for general proximity sensing applications, mere detection of an increasing distance signal is satisfactory. However, applications requiring a speed measurement necessitate determination of the specific Doppler frequency and a calculation of a corresponding speed value. Such homodyne circuits are but among hundreds or thousands of circuits and modulation schemes that in some way carry speed information but which have not been considered practical for providing speed measurements. Accordingly, circuits of a size or cost that are practical for consumer applications such as sports object speed measurement have not been known or available.
Existing Doppler speed measuring devices suffer from loss of accuracy due to the inability to place the unit in the line of the moving object, resulting in a reduction in the speed measurement to the cosine of the angle between the object's velocity vector and the line of the Doppler signal between the unit and the moving object. Further, the Doppler units must be positioned where they are not subjected to damage by collision with the object.
Accordingly, a need exists for a low cost, effective, small size, low power device useful for measuring and displaying the speed of objects in consumer applications such as sports and sports training.
SUMMARY OF THE INVENTION
A primary objective of the present invention is to provide a small size, low cost, low power device for measuring object speed that is practical for consumer applications such as sports. It is a particular objective of the present invention to provide a sports radar unit for measuring and displaying the velocity magnitude or speed of a sports object such as a baseball. Further objectives of the invention are to provide such a speed measurement apparatus and method for measurement of baseball speed, baseball bat speed, for calibrating paint ball marker speed, for martial arts punch and kick speed measurements and other applications, particularly in training.
According to principles of the present invention, there is provided a CW Doppler radar speed sensor that is small in size, low in cost, low in power consumption and radiated energy, that measures and displays the speed of an object such as a baseball and displays the measured speed to a user. Further according to principles of the present invention, a device is provided that is adapted for mounting at or near the path or point of reception of the moving object, or at the “target point” at which the moving object is directed. Such positioning facilitates the use of a low power, short range signal and accurate velocity measurement. The unit preferably transmits and receives RF energy in a microwave frequency range, preferably of a frequency of approximately 2.4 GHz or 5.8 GHz or higher, such as in the 10-25 GHz range.
The device according to one preferred embodiment of the invention, includes a radar transmitter and receiver that employs a single simple CW Doppler homodyne circuit preferably having an oscillator-detector that is based on a single transistor, which utilizes resonant circuit elements of the oscillator as an antenna to radiate energy into free-space. A portion of the radiated energy strikes the nearby moving object and is reflected back to the oscillator-antenna circuit where it is mixed with the oscillator signal. The coherent relationship of the transmitted and received signals in a simple homodyne circuit produces a Doppler frequency modulation as the distance to the moving object changes.
The preferred embodiment of the present invention makes use of the phenomena whereby, at a given separation distance between the radar and the moving object, the received object-reflected signal is exactly in-phase with, and reinforces, the oscillator signal, but as the separation distance changes by each one-quarter wavelength of the transmitted signal, the total two-way travel distance to the object and back changes by one-half wavelength, resulting in an out-of-phase or canceling relationship between the received and transmitted signals. Each distance change of one-half wavelength results in a two-way radar round trip change of one wavelength, thus producing one complete cycle of modulation. As the distance to the moving object changes by successive one-half wavelength increments, multiple cycles of modulation are produced. The frequency of this modulating signal is the Doppler frequency, which is equal to the velocity of the moving object expressed in terms of one-half wavelengths of the transmitted signal as follows:
f
D
=
v
λ
t
/
2
=
2
vf
t
c
where: f
D
is the frequency of Doppler modulation,
v is the relative velocity of the moving object,
&lgr;
t
is the wavelength of the transmitted signal,
f
t
is the frequency of the transmitted signal,
c is the magnitude of the velocity of electromagnetic energy propagating in sur
Kwok Helen
Sports Sensors, Inc.
Wood Herron & Evans L.L.P.
LandOfFree
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