Ultra-sonic distance measuring apparatus and method

• US 4,677,599 A
• Filed: 06/19/1985
• Issued: 06/30/1987
• Est. Priority Date: 06/20/1984
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Kobayashi, Hiroshi, Obayashi, Hiroaki
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Pihulic, Daniel T.
• Application Number:
  US06/746,403
• Time in Patent Office: 741 Days
• Field of Search: 367/97-99, 367/84
• US Class Current: 367/99
• CPC Class Codes: B60G 2400/252 vertical
• CPC Class Codes: B60G 2400/821 Uneven, rough road sensing affecting vehicle body vibration
• CPC Class Codes: B60G 2401/176 Radio or audio sensitive means, e.g. Ultrasonic
• CPC Class Codes: G01S 15/08 Systems for measuring distance only indirect measurement G01S15/46
• CPC Class Codes: G01S 7/526 Receivers
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50

Abstract

An ultra-sonic sensor includes a driver circuit outputting a high-frequency driver signal which orders a transmitter to transmit ultra-sonic waves toward a target object. The driver circuit also sends the driver signal to a receiver. The driver signal is superimposed on a receiver signal. The receiver differentiates the receiver signal and compares the differentiated receiver signal level to a threshold level to detect reception of the reflected ultra-sonic wave. The receiver also detects when the transmitter is actively transmitting the ultra-sonic waves toward the object and disables the aforementioned comparison at such times. Accordingly, by comparing the differentiated receiver signal level with the threshold, the influence directly transmitted ultra-sonic waves on detection of the reflected ultra-sonic wave is successfully avoided. In addition, by interrupting the comparison during a period in which the transmitter is transmitting the ultra-sonic waves, the threshold level can be low enough to allow the system to detect the reflected ultra-sonic wave with great sensitivity.

Claims

1. An ultra-sonic distance measuring apparatus comprising:

means for producing a trigger signal at a given timing and for a given duration;

means for transmitting ultra-sonic waves toward an object in response to said trigger signal;

means for receiving reflected ultra-sonic waves reflected by the object and producing a receiver signal having a value indicative of the amplitude of the received ultra-sonic waves;

means for superimposing said trigger signal on said receiver signal to produce a superimposed signal;

means for rectifying said superimposed signal to produce a rectified signal;

means for differentiating said rectified signal to produce a differentiated signal;

means for comparing said differentiated signal with a predetermined threshold level and producing a comparator signal when said differentiated signal exceeds said threshold level;

means for blocking said comparator signal during said given duration of said trigger signal; and

means for measuring elapsed time between the onset of said trigger signal and the onset of said comparator signal to derive the distance to said object on the basis of said elapsed time.

2. An ultra-sonic distance measuring method comprising the steps of:

producing a trigger signal at a given timing and for a given duration;

transmitting ultra-sonic waves toward an object in response to said trigger signal;

receiving reflected ultra-sonic waves reflected by the object and producing a receiver signal having a value indicative of the amplitude of the received ultra-sonic waves;

superimposing said trigger signal on said receiver signal to produce a superimposed signal;

rectifying said superimposed signal to produce a rectified signal;

differentiating said rectified signal to produce a differentiated signal;

comparing said differentiated signal with a predetermined threshold level and producing a comparator signal when said differentiated signal exceeds said threshold level;

blocking said comparator signal during said given duration of said trigger signal;

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measuring elapsed time between the onset of said trigger signal and the onset of said comparator signal to derive the distance to said object on the basis of said elapsed time.