Echo recognition system

• US 4,380,807 A
• Filed: 05/26/1981
• Issued: 04/19/1983
• Est. Priority Date: 10/03/1979
• Status: Expired due to Term

• Current Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Original Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Inventors: Reynard, John M.
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US06/266,901
• Time in Patent Office: 693 Days
• Field of Search: 367/96, 367/97, 367/99, 367/901, 367/100, 343/5 VQ, 364/517
• US Class Current: 367/97
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50

Abstract

An echo-type range finding system is rendered unresponsive to spurious signals and electronic noise, and has its object distance determining accuracy improved by rejecting signals that do not persist for a predetermined period of time.

Claims

1. A method of detecting a previously transmitted signal of energy returning from a selected target in the presence of energy signals from the source of other than the target, comprising the steps of:

continuously sampling said returning target signal for a number of consecutive time intervals that are of very short time duration relative to the total time duration of said target signal;

establishing that the sampled target signal magnitude increases between consecutive sampling intervals;

establishing that the rate of increase of target signal magnitude between consecutive sampling intervals is greater than or equal to a predetermined rate of increase; and

establishing that said signal magnitude increase and said rate of signal magnitude increase between consecutive sampling intervals is continuous for at least a predetermined portion of the total time duration of said returning target signal.

2. In a ranging system having means for transmitting a burst of energy toward a selected target and for then receiving energy so as to detect an echo from said target, the improvement wherein said transmitting and receiving means includes:

means for providing a sum signal by summing a received signal over a number of consecutive sampling intervals of very short duration relative to the anticipated duration of an echo from a typical target; and

means for identifying an echo as received from said selected target only when said sum signal progressively increases during each consecutive interval over a predetermined time.

3. The improvement of claim 2 wherein said means for identifying an echo includes means for identifying an echo as received from said target only when said sum signal progressively increases over said consecutive intervals at a rate equal or greater than a predetermined positive rate.

4. The improvement of claim 3 wherein said means for identifying an echo includes returning said sum signal to an initial value each time said sum signal fails to increase or the rate of increase, during any given interval, is less than said predetermined rate.

5. The improvement of claims 2, 3 or 4 including means for determining the time of occurrence of the leading edge of the actual echo by subtracting said predetermined time from the time at which the echo is identified by said means for identifying an echo as received from said selected target.

6. A ranging method for detecting an echo from a selected target in the presence of spurious signals, said method comprising the steps of:

summing the energy of received signals over a number of consecutive sampling intervals of short duration relative to the anticipated duration of an echo from a typical target so as to provide a sum signal; and

establishing that an echo is received from said selected target only when said sum signal increases during each consecutive interval over a predetermined period of time.

7. The method of claim 6 wherein said establishing step includes comparing the rate of increase of said sum signal with a predetermined positive rate and identifying an echo as received from said target only when the rate of increase of said sum signal in each of said consecutive intervals exceeds said predetermined positive rate.

8. The method of claim 7 including the step of returning said sum signal to an initial value each time the rate of increase during any given interval is less than said predetermined positive rate.

9. The method of claim 7 wherein said predetermined period of time is a substantial portion of the anticipated duration of the echo.

10. The method of claim 6 or 7 wherein the leading edge of the actual echo is identified as occurring at a time equal to said predetermined time prior to the point of establishing that an echo is received from said selected target.