Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With time interval measuring means
Reexamination Certificate
1998-10-16
2001-11-06
Lobo, Ian J. (Department: 3642)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With time interval measuring means
C073S597000
Reexamination Certificate
active
06314055
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to range measuring systems and more particularly to range measuring systems wherein range is determined by measuring the time of arrival of wave energy.
As is known in the art, range measuring systems have a wide range of applications. One such system includes a transmitter for transmitting a pulse of wave energy, such as a radar or sonar pulse, directing such pulse towards an object, detecting a reflection by the object of such pulse, measuring the time of arrival of the detected reflection, and determining the range to the object from such measured time of arrival. In this case, called pulse-echo mode, the range is calculated as half the roundtrip travel time, times the speed of propagation. In other systems called transmit-receive mode, the range to the actual source of the wave energy itself is detected. One such system is described in U.S. Pat. No. 5,280,457, issued Jan. 18, 1994, and entitled Position Detection System and Method. Such U.S. Patent describes the use of a peak detector to detect the peak of the wave energy and from the detected peak, the time of arrival of the wave energy. In such system, the peak of the wave energy is determined using a differentiator circuit. Another system is described in U.S. Pat. No. 5,142,506, issued Aug. 25, 1992 and entitled Ultrasonic Position Locating Method and Apparatus Therefor.
SUMMARY OF THE INVENTION
In accordance with the invention, a system is provided for determining a time of arrival of a waveform having a predetermined shape. The waveform has a rising amplitude portion and terminating portion. The waveform may be attenuated as such waveform passes through a medium while such medium maintains the predetermined shape of the waveform, except for a scale factor representing the attenuation. The system includes a detector for detecting a predetermined time rate of change characteristic of the waveform envelope during the rising portion of such waveform. A processor is typically provided for determining the time of arrival of the waveform in response to the detected predetermined time rate of change characteristic of the waveform.
With such system, reception of the waveform is detected before any reflection from an echo reflecting surface interferes with, and thereby distorts, the characteristics of the waveform around the peak of the envelope or trailing portion of such received waveform. Thus, the system provides more accurate detection of the received waveform compared with a system which relies solely on detection of the peak of the envelope of such received waveform.
In accordance with another feature of the invention, a method is provided for detecting a waveform having a predetermined shape. The waveform includes a rising portion and terminating portion, such waveform having been attenuated as such waveform passes through a medium while the medium maintains the predetermined shape of the waveform. The method includes detecting a predetermined time rate of change characteristic of the waveform during the rising portion of such waveform.
In accordance with another feature of the invention, a system is provided for determining range to a source of wave energy. The system includes a transmitter for transmitting a burst of wave energy in response to a trigger signal. A receiver is provided for determining a time of arrival of such energy, and from such determined time of arrival, the range to the source. The receiver includes: an envelope detector for detecting an envelope of the burst; a network for producing an output in response to a detection point on the detected envelope occurring prior to a peak in the detected envelope; a timer, responsive to the trigger signal and the network output for determining the time of flight of the burst; and, a processor for calculating from the determined time of flight the range travelled by the transmitted wave energy. The temporal location of the detection point is unaffected by attenuation of the burst waveform.
In accordance with another feature of the invention, the receiver includes: an envelope detector for detecting an envelope of the burst; and, a differentiator network for producing an output in response to the first peak of the nth derivative of the detected envelope, where n is an integer greater than zero.
In accordance with another feature of the invention, the receiver includes a valid burst detector for confirming the reception of the burst and wherein the exact time of arrival measured by the network prior to the burst confirmation is not transmitted until after the reception of a valid burst has been confirmed, in order to reduce false alarms.
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Foxlin Eric
Moore Russell L.
Fish & Richardson P.C.
Intersense, Inc.
Lobo Ian J.
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