ULTRASOUND TRANSDUCER TEMPERATURE COMPENSATION METHODS, APPARATUS AND PROGRAMS

• US 20040064280A1
• Filed: 09/30/2002
• Published: 04/01/2004
• Est. Priority Date: 06/03/1999
• Status: Active Grant

• Current Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Original Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Inventors: Seip, Ralf, Watts, Russell C.
• Granted Patent: US 6,782,332 B2
• Time in Patent Office: Days
• US Class Current: 702/103
• CPC Class Codes: B06B 1/0215 for generating pulses, e.g. bursts of oscillations, envelopes
• CPC Class Codes: B06B 2201/40 with testing, calibrating, safety devices, built-in protection, construction details
• CPC Class Codes: B06B 2201/51 Electrostatic transducer
• CPC Class Codes: B06B 2201/70 Specific application
• CPC Class Codes: B60H 1/00742 by detection of the vehicle occupants' presence; by detection of conditions relating to the body of occupants, e.g. using radiant heat detectors
• CPC Class Codes: B60H 1/00771 the input being a vehicle position or surrounding, e.g. GPS-based position or tunnel
• CPC Class Codes: B60H 1/00814 Control systems or circuits characterised by their output, for controlling particular components of the heating, cooling or ventilating installation
• CPC Class Codes: B60R 21/01536 using ultrasonic waves
• CPC Class Codes: B60W 2040/0818 Inactivity or incapacity of driver
• CPC Class Codes: B60W 30/18054 at stand still, e.g. engine in idling state hill holding B60W30/18118
• CPC Class Codes: B60W 40/09 Driving style or behaviour
• CPC Class Codes: G01S 7/52006 with provision for compensating the effects of temperature
• CPC Class Codes: G01S 7/5205 Means for monitoring or calibrating
• CPC Class Codes: G01S 7/521 Constructional features

Abstract

Method, apparatus and computer programs are described for compensating for the effect of temperature on the sensitivity of electrostatic ultrasound (US) transducers, particularly as used in an automotive occupancy sensing (AOS) systems for sensing the nature or type of occupant and the location of the occupant with respect to the vehicle interior. The invention permits the AOS to classify the occupancy state of the vehicle from a US echo signal substantially free of the effects of temperature on signal amplitude. A capacitive divider or voltage monitor is employed to measure the capacitance of the transducer. The voltage monitor output is used by the scaling algorithm of a compensator to determine the scaling factor to be applied to the US transducer signal to compensate for the effect of temperature on the transducer sensitivity. Calibration procedures and software are disclosed for determining the coefficients of the scaling algorithm to compensate for temperature effects and also to compensate for installation factors, transducer manufacturing variations, and circuit board effects. The system disclosed is useful for other types of signal processing in addition to temperature compensation of AOS ultrasonic signals, and may be used in other ranging devices such as cameras, golf or binocular range finders, and measuring devices and instruments.

Claims

1. In an ultrasound electrostatic transducer circuit for transmitting ultrasound pulses and receiving ultrasound echo returns, said transducer circuit producing an ultrasound transducer output signal in a ultrasound signal output line, a capacitive divider sub-circuit improvement comprising:

(a) a first capacitor and a second capacitor electrically connected in series between said ultrasound signal output line and ground; and

(b) a voltage signal output line electrically connected between said first and said second capacitor to produce a transducer voltage monitor output signal during transducer circuit operation.

2. A capacitive divider sub-circuit as in claim 1, wherein said voltage monitor output signal is used to measure the capacitance of said transducer.

3. A capacitive divider sub-circuit as in claim 1, wherein said voltage monitor output signal is used to measure the variation in the sensitivity of said transducer due to variation in the temperature of said transducer.

4. A capacitive divider sub-circuit as in claim 1, wherein said voltage monitor output signal is used to compensate for variation in the sensitivity of said transducer due to variation in the temperature of said transducer.

5. A capacitive divider sub-circuit as in claim 1, wherein:

a) said ultrasound electrostatic transducer circuit is operated in communication with an ultrasound echo signal processing means into which said ultrasound output signal is input;

b) said echo signal processing means has a maximum usable input signal magnitude; and

c) the capacitances of said first and second capacitors are selected so that the magnitude of said voltage monitor output signal during said transmitted ultrasound pulses does not substantially exceed said maximum usable input signal magnitude.

6. A capacitive divider sub-circuit as in claim 5, wherein:

a) said ultrasound echo signal processing means includes AOS electronics having an analog-to-digital converter for digitizing said ultrasound transducer output signal; and

b) said analog-to-digital converter has a maximum digitizing level; and

c) said maximum usable input signal magnitude is said maximum digitizing level.

7. An improved automotive occupancy sensor system having an ultrasound electrostatic transducer sensor circuit for transmitting ultrasound pulses and receiving ultrasound echo returns and an ultrasound signal output line for transmitting an ultrasound transducer output signal from said sensor circuit to a feature extraction means for extracting ultrasound echo return features for occupancy state classification, the improvement comprising:

a) a voltage scaling sub-circuit connected to said transducer circuit to produce a voltage monitor signal in a voltage monitor signal line;

b) a compensation means;

c) said ultrasound signal output line and said voltage monitor signal line each connecting to and transmitting its respective signal to said compensation means;

d) said compensation means scaling the amplitude of said ultrasound output signal in response to said voltage monitor signal to produce a scaled ultrasound output signal substantially compensated for the effects of variation in the temperature of said transducer; and

e) said scaled ultrasound output signal being transmitted from said compensation means to said feature extraction means.

8. An improved automotive occupancy sensor system in claim 7, wherein said voltage monitor signal includes a scaled representation of said ultrasound transducer output signal during said ultrasound pulse transmission.

9. An improved automotive occupancy sensor system in claim 8, wherein:

a) said voltage scaling sub-circuit includes a capacitive divider sub-circuit coupled to said transducer circuit to produce said voltage monitor signal; and

b) said capacitive divider sub-circuit includes;

i) a first capacitor and a second capacitor electrically connected in series between said ultrasound signal output line and ground, and

ii) said voltage monitor signal line electrically connected between said first and said second capacitors to produce said voltage monitor signal.

10. An improved automotive occupancy sensor system as in claim 9, wherein:

a) said ultrasound signal output line and said voltage monitor signal line are combined in a multiplexer to form a multiplex signal containing both ultrasound signal data and voltage monitor signal data;

b) said multiplex signal is transmitted to said compensation means; and

c) said compensation means includes means for separately detecting and processing said ultrasound signal data and said voltage monitor signal data.

11. An improved automotive occupancy sensor system as in claim 10, wherein:

a) said automotive occupancy sensor system includes an analog-to-digital converter;

b) said multiplex signal is transmitted to said analog-to-digital converter and converted to a digital multiplex signal; and

c) said digital multiplex signal is transmitted to said compensation means.

12. An improved automotive occupancy sensor system as in claim 11, wherein:

a) said analog-to-digital converter has a maximum digitizing level; and

b) the capacitances of said first and second capacitors are selected so that the magnitude of said voltage monitor signal during said transmitted ultrasound pulses does not substantially exceed said maximum digitizing level.

13. An improved automotive occupancy sensor system as in claim 7, wherein said compensation means includes a computer usable medium having computer readable program code means embodied thereon for carrying out a compensation algorithm to scale the amplitude of said ultrasound signal output in response to said voltage monitor signal output.

14. A method of compensation for the effects of temperature-dependent variation in sensitivity of an ultrasound electrostatic transducer sensor circuit for transmitting ultrasound pulses and receiving ultrasound echo signals, comprising in any operative order:

a) providing a capacitive divider sub-circuit connected to said sensor circuit to produce a voltage output signal during said ultrasound pulse transmission;

b) measuring the amplitude of said voltage output signal of said capacitive divider sub-circuit; and

c) scaling the amplitude of said ultrasound echo signal in response to said voltage output signal to produce a scaled ultrasound echo signal output substantially compensated for the effects of variation in the temperature of said transducer.

15. A method of compensation for the effects of temperature-dependent variation in sensitivity of an ultrasound electrostatic transducer circuit for transmitting ultrasound pulses and receiving ultrasound echo returns, said transducer circuit producing an ultrasound transducer output signal in a ultrasound signal output line, comprising in any operative order:

a) measuring the amplitude of said ultrasound transducer output signal during said transmitted ultrasound pulses; and

b) scaling the amplitude of said ultrasound transducer output signal in response to said measured amplitude of said ultrasound transducer output signal to produce a scaled ultrasound transducer output signal that is substantially compensated for the effects of variation the sensitivity of said transducer due to variation in the temperature of said transducer circuit.

16. A method of compensation as in claim 15, wherein:

a) said measuring step includes measuring the amplitude of said ultrasound transducer output signal by means of a capacitive divider sub-circuit connected to said transducer circuit to produce a voltage monitor signal;

b) said voltage monitor signal includes a scaled transducer voltage signal during said ultrasound pulse transmission.

17. A method of compensation as in claim 16, comprising the steps of:

a) combining said voltage monitor signal and said ultrasound transducer output signal to produce a combined signal;

said combined signal includes at least;

i) voltage monitor signal information during said transmitted pulse; and

ii) ultrasound transducer output signal information during said received ultrasound echo returns.

b) digitizing said combined signal to produce a digital combined signal.

c) separately detecting said voltage monitor signal information and said ultrasound transducer output signal information from said digital combined signal.

18. A method of compensation as in claim 17, wherein:

a) said combining step includes combining said signals by multiplex switching to produce a signal in which said voltage monitor signal information alternates with said ultrasound transducer output signal information.

19. A data processing system for compensating for the effects of variation in transducer sensitivity due to variation in temperature, in association with an ultrasound electrostatic transducer sensor circuit for transmitting ultrasound pulses and receiving ultrasound echo returns, said transducer circuit producing an ultrasound transducer output signal, said data processing system comprising:

a) a capacitive divider sub-circuit connected to said transducer circuit to produce a voltage monitor signal;

b) a converter to convert both of said ultrasound transducer output signal and said voltage monitor signal to digital signals, including voltage monitor signal amplitude characteristics; and

;

c) a computer processor which processes said digitized signals, said processor including a memory storage medium having stored therein a compensation algorithm relating the transducer sensitivity to the amplitude of said voltage monitor signal, and said processor scales the amplitude of said ultrasound transducer output signal to produce a compensated ultrasound signal by computing and applying a scaling factor based on said compensation algorithm and said voltage monitor amplitude.

20. A data processing system as in claim 19, wherein said computer processor evaluates a pre-selected polynomial equation which expresses said scaling factor value as a function of said voltage monitor signal amplitude to scale said amplitude of said ultrasound transducer output signal, and produces a temperature compensated transducer signal by amplifying said ultrasound transducer output signal in proportion to said scaling factor.

21. A method of detecting the existence of at least one of an open circuit state and a shorted state of an ultrasound electrostatic transducer sensor circuit for transmitting ultrasound pulses and receiving ultrasound echo signals, comprising in any operative order:

a) providing a capacitive divider sub-circuit connected to said sensor circuit;

b) establishing a pre-selected amplitude limit of said voltage monitor signal corresponding to at least one of an open circuit state and a shorted state of said transducer circuit; and

c) comparing the amplitude of said voltage monitor signal with at least one of a pre-selected open-circuit limit voltage and a pre-selected short-circuit limit voltage to determine if said amplitude is beyond said amplitude limit.

22. A method of substantially reducing the magnitude of audible clicks produced during biasing of an ultrasound electrostatic transducer sensor circuit for transmitting ultrasound pulses and receiving ultrasound echo signals, comprising in any operative order:

a) providing a capacitive divider sub-circuit connected to said sensor circuit;

b) monitoring said voltage monitor signal to determine transducer bias voltage; and

c) regulating said bias voltage of said transducer in response to said voltage monitor signal to substantially reduce the magnitude of audible clicks.

23. A method of to substantially eliminate pulse-to-pulse amplitude variation of an ultrasound electrostatic transducer sensor circuit for transmitting ultrasound pulses and receiving ultrasound echo signals, comprising in any operative order:

a) providing a capacitive divider sub-circuit connected to said sensor circuit;

b) establishing a pre-selected voltage monitor signal amplitude corresponding to a pre-selected transducer bias voltage state; and

c) adjusting said bias voltage of said transducer in response to said voltage monitor signal to reach said pre-selected voltage monitor signal amplitude prior to the transmission of each ultrasound pulse to substantially eliminate pulse-to-pulse amplitude variation.

24. A computer program product for compensating for the effects of variation in transducer sensitivity due to variation in temperature and operating on a computer processor system including memory storage in association with ultrasound transducer driving circuitry, said driving circuitry producing a digitized voltage monitor signal representing transducer voltage during transducer ultrasound transmission and a digitized transducer output signal,

said computer program product comprising a computer usable medium having computer readable program code embodied in said medium, said computer readable program code comprising:

a) a first program code means for causing the computer system to detect the amplitude of said digitized voltage monitor signal;

b) a second program code means for causing the computer system to detect the amplitude of said digitized transducer output signal;

c) a third program code means for causing the computer system to compute a scaling factor based on a compensation algorithm relating the transducer sensitivity to the amplitude of said voltage monitor signal; and

d) a fourth program code means for causing the computer system to scale the amplitude of said digitized transducer output signal by amplifying said digitized transducer output signal in proportion to said scaling factor to produce a temperature compensated transducer output signal.

25. A computer program product as in claim 24, wherein said compensation algorithm of said third program code means includes:

a) program code means for causing the computer system to read from a memory storage medium at least one coefficient value for a variable term of a polynomial equation, which coefficient value is pre-calibrated to represent said temperature dependency of said transducer sensitivity;

b) program code means for causing the computer system to substitute said value for said coefficient in said polynomial equation; and

c) program code means for causing the computer system to substitute said detected voltage monitor signal amplitude for the independent variable of said polynomial equation; and

d) program code means for causing the computer system to determine the value of said scaling factor by evaluating said equation.