Ultrasonic sonar and method using transmission frequency different from reverberation frequency

• US 6,490,226 B2
• Filed: 01/24/2001
• Issued: 12/03/2002
• Est. Priority Date: 02/04/2000
• Status: Expired due to Fees

• Current Assignee: Nippon Soken, Inc. (DENSO Corporation)
• Original Assignee: Nippon Soken, Inc. (DENSO Corporation)
• Inventors: Chiba, Tanemichi, Kani, Hiroyuki, Tsuzuki, Takeo, Iwasaki, Nobuyuki, Asakura, Fumio
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US09/767,751
• Publication Number:
  US 20010012238A1
• Time in Patent Office: 678 Days
• Field of Search: 367/99, 367/13, 367/97, 735/97
• US Class Current: 367/97
• CPC Class Codes: G01S 15/931 of land vehicles
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50

Abstract

An ultrasonic sonar has a transceiver equipped with an ultrasonic oscillator. An ultrasonic wave is transmitted from the transceiver. The ultrasonic wave reflected from an obstacle is received by the ultrasonic oscillator to detect the obstacle. The transmission frequency of the ultrasonic wave is set to be different from the reverberation frequency. When the obstacle is detected, a microcomputer converts the analog signal received by the ultrasonic oscillator into a digital signal, performs a frequency transform of this signal by Fourier transform to extract only the transmission frequency component, and performs an inverse transform.

Claims

1. An ultrasonic sonar for detecting an obstacle comprising:

an ultrasonic oscillator for transmitting an ultrasonic wave and receiving an ultrasonic wave reflected from the obstacle, the ultrasonic oscillator having a reverberation frequency; and

processing means for causing the ultrasonic oscillator to transmit the ultrasonic wave at a transmission frequency different from the reverberation frequency, converting an analog signal received by the ultrasonic oscillator into a digital signal on detection of the obstacle, and extracting only a component of the transmission frequency from the converted signal by digital signal processing.

2. The ultrasonic sonar of claim 1, wherein:

the processing means calculates a distance to the obstacle from a period of time between a start of transmission of the ultrasonic wave and an instant when level of the ultrasonic wave of the transmission frequency extracted by the digital signal processing exceeds a threshold level.

3. The ultrasonic sonar of claim 1, wherein:

the transmission frequency is switched from a first transmission frequency to a second transmission frequency that is more differentiated from the reverberation frequency than the first transmission frequency, if presence of an obstacle within a predetermined distance is detected by using the first transmission frequency.

4. The ultrasonic sonar of claim 1, further comprising:

a memory for storing a transmission frequency different from the reverberation frequency,

wherein the ultrasonic wave is transmitted from the ultrasonic oscillator at the transmission frequency stored in the memory.

5. The ultrasonic sonar of claim 4, wherein:

the transmission frequency stored in the memory is set according to the reverberation frequency.

6. The ultrasonic sonar of claim 1, wherein:

the signal received by the ultrasonic oscillator is rejected during a period between end of transmission of the ultrasonic wave and arrival of the ultrasonic wave reflected within a predetermined zone.

7. The ultrasonic sonar of claim 6, wherein:

the signal received by the ultrasonic oscillator during the period is rejected before the signal is converted from analog to digital form.

14. The ultrasonic sensor of claim 1, wherein the processing means calculates a distance to the obstacle by using a fast Fourier Transform and an inverse fast Fourier transform.

8. A method of transmitting an ultrasonic wave from an ultrasonic oscillator included in an ultrasonic sonar and for receiving an ultrasonic wave reflected from an obstacle by the ultrasonic oscillator to detect an obstacle, the method comprising the steps of:

causing the ultrasonic oscillator to transmit an ultrasonic wave with a given frequency;

calculating a reverberation frequency;

setting a transmission frequency to a frequency different from the calculated reverberation frequency and storing the set transmission frequency in a memory;

causing the ultrasonic oscillator to transmit the ultrasonic wave of the frequency stored in the memory;

converting an analog signal received by the ultrasonic oscillator to a digital signal; and

calculating a distance to an obstacle, by which the ultrasonic wave is reflected, based on the digital signal by using a fast Fourier Transform and an inverse fast Fourier Transform.

9. The method of claim 8, wherein the calculating a distance to an obstacle further comprises:

extracting only a component of the transmission frequency corresponding to the distance to the obstacle; and

using the extracted component in the calculating of the distance.

10. The method of claim 8, wherein the setting of the transmission frequency includes switching the transmission frequency from a first transmission frequency to a second transmission frequency that is further differentiated from the reverberation frequency than the first transmission frequency, if a presence of the obstacle within a predetermined distance is detected by using the first transmission frequency.

11. The method of claim 9, wherein the calculating a distance of an obstacle includes calculating the distance to the obstacle from a period of time between a start of transmission of the ultrasonic wave and an instant when a signal level of the component of the transmission frequency resulting from the extracting of only a component of the transmission frequency corresponding to the distance to the obstacle exceeds a threshold level.

12. The method of claim 10, further comprising;

rejecting signals received by the ultrasonic oscillator during a period between an end of transmission of the ultrasonic wave and an arrival of the ultrasonic wave reflected within a predetermined zone.

13. The method of claim 10, further comprising;

rejecting signals received by the ultrasonic oscillator before the converting of an analog signal received by the ultrasonic oscillator to a digital signal.