Ultrasonic distance sensor with dual burst noise rejection

• US 4,679,175 A
• Filed: 12/13/1984
• Issued: 07/07/1987
• Est. Priority Date: 12/13/1984
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Krzyanowski, Robert V., Eder, Kenneth C.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Pihulic, Daniel T.
• Application Number:
  US06/681,163
• Time in Patent Office: 936 Days
• Field of Search: 367/95, 367/105, 367/112, 367/151, 367/97-99, 367/902
• US Class Current: 367/98
• CPC Class Codes: G01S 15/108 using more than one pulse per sonar period
• CPC Class Codes: G01S 2007/52014 involving a reference reflector integrated in the sensor or transducer configuration
• CPC Class Codes: G01S 7/52006 with provision for compensating the effects of temperature
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50
• CPC Class Codes: Y10S 367/902 Speed of sound compensation

Abstract

An ultrasonic distance sensing method and apparatus are disclosed in which a transducer periodically transmits a pair of bursts of acoustic energy along an acoustic path toward a target object, an echo of the first acoustic burst in each burst pair is used to establish a peak reference level, and an echo of the second burst in each pair is used to determine distance to the target object only if its level exceeds a predetermined fraction of the peak reference level.

Claims

1. An ultrasonic sensor comprising:

transducer means including an electroacoustic transducer for transmitting burst of acoustic energy along a predetermined path in response to electrical drive pulses and converting echoes of the transmitted burst into corresponding electrical signals;

a reference target located in the predetermined path closer to said transducer means than any intended target object for reflecting a portion of the acoustic energy transmitted by said transducer means back toward said transducer means;

transmit circuitry having a control terminal, said transmit signal circuitry being operable in response to a first signal at the control terminal to supply a first electrical drive pulse to said electroacoustic transducer so as to cause it to transmit a first burst of acoustic energy;

receiver circuitry connected to receive electrical signals produced by said electroacoustic transducer, said receiver circuitry being operable to supply a second signal to the control terminal of said transmit circuitry in response to to receipt by said transducer means of an echo from said reference target of the first burst of acoustic energy, thereby causing said transmit circuitry to supply a second electrical driver pulse and said transducer means to transmit a second burst of acoustic energy, said receiver circuitry including a peak detector operable to establish a peak reference level in response to a first echo signal resulting from receipt of an echo of the first burst of acousitic energy from a target object, said receiver circuitry further including comparator means operable to pass a second echo signal resulting from receipt of an echo of the second burst of acoustic energy from the target object if the level of the second echo signal exceeds a predetermined fraction of the peak reference level;

oscillator means for producing periodic clock signals;

counter means operable to accumulate a first count of the clock signals occurring during a time interval commencing at a predetermined time relative to transmission of the second burst of acoustic energy and ending at a predetermined time relative to receipt of the second echo provided that the second echo signal is passed by said comparator means; and

output means connected to said counter means for producing an indication of distance to the target object based on the first count of clock signals.

2. The ultrasonic sensor of claim 1 wherein:

the first drive pulse supplied by said transmit circuitry is characterized to cause the first burst of acoustic energy transmitted by said electroacousitic transducer to be of a predetermined duration; and

said transmit circuitry is operable to supply the second drive pulse only after an echo of the first burst which exceeds the predetermined duration is received.

3. The ultrasonic sensor of claim 2 wherein:

said receiver circuitry includes an averaging detector operable to establish an average reference level in response to the electrical signals produced by said electroacoustic transducer; and

said comparator means is operable to pass the second echo signal only if its level exceeds the average reference level and a predetermined fraction of the peak reference level.

4. The ultrasonic sensor of claim 3 wherein:

said counter means is further operable to produce a proximity signal when it reaches a second count indicative of a minimum target distance at which range can be measured; and

latch means is provided, said latch means being responsive to the proximity signal and operable to provide an output signal indicating that the target object is too close for a range measurement until the count of clock signals advances to the second count.

5. An ultrasonic sensor comprising:

an electrocousitc transducer adapted to transmit burst of acoustic energy along an acoustic path in response to electrical drive pulses and to convert acoustic energy received from targets in the acoustic path to corresponding electrical echo signals;

a reference target located in the acoustic path closer to said elctroacoustic transducer than any intended target object;

transmit/receive circuitry operable to supply a first electrical drive pulse to said elctroacoustic transducer for causing it to transmit a first burst of acoustic energy, said transmit/receive circuitry responding to receipt by said electroacoustic transducer of an echo of the first burst of acoustic energy from said reference target by supplying a second electrical drive pulse to said electroacoustic transducer for causing it to transmit a second burst of acoustic energy, said transmit/receive circuitry further being operable to receive from said electroacoustic transducer corresponding first and second echo signals due to echoes of the first and second bursts of acoustic energy from a target object in the acoustic path said transmit/receiver circuitry includes means for using the first echo signal to establish validity criteria for the second echo signal;

an output circuit connected to said transmit/receive circuitry and operable to indicate presence of a target object in response to the second echo signal provided that the second echo signal meets validity criteria established in response to the first echo signal.

6. The ultrasonic sensor of claim 5 wherein said transmit/receive circuitry includes:

a peak detector operable to establish a peak reference level based on the level of the first echo signal; and

comparator means operable to compare the level of the second echo signal with the peak reference level and to supply a corresponding signal to said output circuit only if the level of the second echo signal exceeds a predetermined fraction of the peak reference level.

7. The ultrasonic sensor of claim 6 wherein:

said transmit/receive circuitry includes an averaging detector operable to establish an average reference level based on the average level of electrical signals produced by said electroacoustic transducer during an operating cycle; and

said comparator means is operable to compare the level of the second echo signal with the average reference level and supply said corresponding signal only if the level of the second echo signal exceeds the average reference level and a predetermined fraction of the peak reference level.

8. An ultrasonic sensor comprising:

an electroacoustic transducer adapted to transmit acoustic energy along an acoustic path in response to electrical drive signals and to convert reflections of the transmitted acoustic energy from objects in the acoustic path to corresponding electrical detection signals;

reflector means positioned to intercept at least a portion of the transmitted acousitc energy and redirect the intercepted acoustic energy toward a target area, said reflector further being operable to redirect at least a portion of the acoustic energy reflected from objects in the target area toward said transducer;

a reference target proximate said reflector means for reflecting a portion of the acoustic energy transmitted by said electroacoustic transducer back toward said electroacoustic transducer; and

transmit/receiver circuitry operble to supply a first electrical drive signal to said transducer whereby said transducer is caused to transmit a first burst of acoustic energy, said transmit/receive circuitry responding to receipt by said electroacoustic transducer of a reflection of the first burst of acoustic energy from said reference target by supplying a second electrical drive signal to said electroacoustic transducer for causing it to transmit a second burst of acoustic energy, said transmit/ receive circuitry further being operable to produce first and second echo signals in response to echoes of the first and second bursts of acoustic energy respectively from an object in the target area, said transmit/receive circuitry includes means for using the first echo signal to establish validity criteria for the second echo signal and to utilize the second echo signal to determine presence of the object provided that the second echo signal meets validity criteria established in response to the first echo signal.

9. The ultrasonic sensor of claim 8 wherein said transmit/receive circuitry includes:

an averaging detector operable to establish an average reference level in response to the first and second echo signals; and

first comparator means operable to provide an output signal permitting determination of presence of the object only if the level of the second echo signal is higher than the average reference level.

10. The ultrasonic sensor of claim 9 wherein:

a peak detector operable to establish a peak reference level based on the first echo signal is included; and

second comparator means operable to permit a determination of presence of the object only if the level of the second echo signal exceeds the average reference level and peak reference level.

11. A method of ultrasonically determining distance between an electroacoustic transducer and a target object, comprising the steps of:

transmitting a first burst of acoustic energy along an acoustic path toward the target object;

locating a reference target in the acoustic path between the electroacoustic transducer and the target object;

transmitting a second burst of acoustic energy along the acoustic path in response to receipt at the electroacoustic transducer of a reflection of the first burst of acoustic energy from the reference target;

establishing validity criteria from reflections of the first burst of acoustic energy from the target object; and

determining distance to the target object from the time required for reflections of the second burst of acoustic energy to return from the target object, the distance being determined only if the reflectons of the second burst of acoustic energy from the target object meet the validity criteria.

12. The method of claim 11 comprising the further steps of:

establishing a peak reference level based on the level of the reflection of the first burst of acoustic energy from the target object; and

determining distance to the target object only if the level of the reflection of the second burst of acoustic energy from the target object exceeds a predetermined fraction of the peak reference level.

13. The method of claim 12 comprising the further steps of:

establishing an average reference level based on the levels of reflections of the first and second bursts of acoustic energy from the target object during an operating cycle; and

determining distance to the target object only if the level of the reflection of the second burst of acoustic energy from the target object exceeds the average and peak reference levels.