Ultrasound transducer temperature compensation methods, apparatus and programs

• US 6,782,332 B2
• Filed: 09/30/2002
• Issued: 08/24/2004
• Est. Priority Date: 06/03/1999
• Status: Expired due to Fees

• Current Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Original Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Inventors: Watts, Russell C., Seip, Ralf
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): LE, JOHN H
• Application Number:
  US10/261,641
• Publication Number:
  US 20040064280A1
• Time in Patent Office: 694 Days
• Field of Search: 702/39, 702/58, 702/71, 702/99, 702/119, 702/103, 701/47, 600/399, 600/587, 378/98, 363/59, 324/76.23, 324/76.33, 324/77.11, 280/735, 73/492, 736/02, 736/29, 736/31, 736/32
• 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. A method for improving the operation and functionality of an ultrasound sensor system having an electrostatic transducer for transmitting ultrasound pulses, receiving ultrasound echo signals and outputting a transducer signal, and a transducer signal processing circuit, comprising in any operative order:

a) providing a capacitive divider sub-circuit connected to said sensor circuit to produce a voltage monitor output signal, VMON;

b) evaluating and controlling said voltage monitor signal, VMON, to provide reduction in the magnitude of audible clicks, substantially eliminate pulse-to-pulse amplitude variation, detect the existence of at least one of an open circuit state and a shorted state, or measurement of temperature.

2. A method as in claim 1 wherein said step of evaluating and controlling said voltage monitor signal includes 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) 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

b) 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.

3. A method as in claim 1 wherein said step of evaluating and controlling said voltage monitor signal includes 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) monitoring said voltage monitor signal to determine transducer bias voltage; and

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

4. A method as in claim 1 wherein said step of evaluating and controlling said voltage monitor signal includes substantially eliminating 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) establishing a pre-selected voltage monitor signal amplitude corresponding to a pre-selected transducer bias voltage state; and

b) 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.

5. A method as in claim 1 wherein said step of evaluating and controlling said voltage monitor signal, VMON, includes measurement of temperature, comprising the steps of:

a) providing as said electrostatic transducer, a transducer that is calibrated for a temperature scaling factor and providing in said circuit an ultrasound signal compensator having a calibration compensation algorithm employing said scaling factor;

b) activating said signal processing circuit to;

     1) excite said transducer to transmit an ultra-sound ping signal of short duration and

     2) to capacitive-divide and digitize said ping signal in the process of activating said circuit;

c) processing said digitized ping signal to determine VMON of said signal; and

d) determining a temperature value signal from VMON by applying at least one calibration scaling factor value.

6. Method as in claim 5 which includes the added step of converting said temperature value signal to a temperature reading for display.

7. Method as in claim 5 wherein said calibration includes scaling for hardware-specific effects.

8. Method as in claim 5 wherein said VMON is a component of a digitized multi-plexed signal, said signal comprising a digitized form of a transmit ping pulse followed by an ultrasound echo return signal.

9. Method of temperature measurement as in claim 8 wherein said VMON is a signal out of a capacitive divider sub-circuit of said signal processing circuit.

10. Method as in claim 8 wherein VMON signal value range is selected to be within the range of capacity of digital electronics and large enough to have acceptably high resolution of temperature compensation.

11. Method as in claim 5 wherein the temperature compensation algorithm is based on a parabolic scaling relationship between voltage monitor signal values and temperature.

12. Method as in claim 11 wherein said algorithm includes both off-line calibration parameters and on-line calibration parameters.

13. Method as in claim 5 wherein the scaling factor is an overall scaling factor that comprises at least one hardware-specific scalar and at least one temperature-dependant scalar.

14. Method as in claim 13 wherein said scalars are selected from parameters determined during calibration and V_m, wherein V_m is the magnitude of a digitized.

15. Method as in claim 14 wherein a plurality of calibration parameters are computed from VMON over a range of calibration temperatures.

16. A method as in claim 5 comprising the steps of:

a) monitoring changes in capacitance during operation of said circuit to provide a signal indicative of a temperature value; and

b) outputting said temperature value to a display device or memory storage device as a measured temperature.