Method and system for processing measurement signals to obtain a value for physical parameter

• US 6,481,289 B2
• Filed: 01/17/2002
• Issued: 11/19/2002
• Est. Priority Date: 11/22/1996
• Status: Expired due to Fees

• Current Assignee: Perceptron Incorporated (Atlas Copco AB)
• Original Assignee: Perceptron Incorporated (Atlas Copco AB)
• Inventors: White, Jeffrey S., LaPlant, Frederick P., Dixon, John W.
• Primary Examiner(s): Larkin, Daniel S.
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US10/052,047
• Publication Number:
  US 20020152813A1
• Time in Patent Office: 306 Days
• Field of Search: 735/79, 735/96, 735/97, 735/98, 735/99, 736/02, 736/53, 736/57, 250/231.1, 356/381, 356/382, 356/355, 356/357, 356/345
• US Class Current: 73/602
• CPC Class Codes: G01B 11/0666 using an exciting beam and a detection beam including surface acoustic waves [SAW]
• CPC Class Codes: G01B 17/025 for measuring thickness of coating
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/0228 Aqueous liquids
• CPC Class Codes: G01N 2291/0231 Composite or layered materials
• CPC Class Codes: G01N 2291/0237 Thin materials, e.g. paper, membranes, thin films
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 2291/02818 Density, viscosity
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/101 one transducer
• CPC Class Codes: G01N 29/0681 by acoustic microscopy, e.g. scanning acoustic microscopy
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• CPC Class Codes: G01N 29/225 Supports, positioning or alignment in moving situation
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency
• CPC Class Codes: G01N 29/46 : by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01N 29/50 : using auto-correlation techniques or cross-correlation techniques

Abstract

In a measurement system wherein time-varying physical signals containing frequency information related to a physical parameter of an object are measured to obtain corresponding time-varying measurement signals, a method and system are disclosed for processing the measurement signals to obtain a value for the physical parameter by first extracting the frequency information from the measurement signals. The frequency information includes at least one desired frequency and its amplitude and decay rate. Then, the frequency information is converted to a value for the physical parameter. The measurement signals are discrete time ultrasonic signals. Extraction is performed by transforming the ultrasonic signals to a Z-domain and converting at least one zero or pole in the Z-domain to the at least one frequency and its decay rate.

Claims

1. A method for determining properties of an object having a surface that transitions from a substantially fluid state to a substantially solid state, the method comprising:

producing motions in the surface of the object during the substantially fluid state without touching the fluid;

collecting time-varying signals responsive to the surface motions produced during the substantially fluid state; and

calculating a value for at least one substantially solid state property of the object based on the time-varying signals collected in the substantially fluid state.

2. The method of claim 1, wherein the surface motions are produced by ultrasound.

3. The method of claim 2, wherein the surface motions are produced by the ultrasound without touching and without damaging either state of the surface.

4. The method of claim 1, wherein the substantially fluid state is a saturated state characterized by the presence of a solvent and the substantially solid state is an unsaturated state characterized by a substantial decrease in the presence of the solvent.

5. The method of claim 1, further comprising determining a decay rate and a frequency for the time-varying signals collected in the substantially fluid state by pole-zero modeling of the time-varying signals, wherein pole-zero modeling comprises:

modeling the time-varying signals as exponentially decaying sinusoids;

computing poles of the modeled time-varying signals;

least-squares fitting a linear prediction filter for the poles;

determining zeros for the filter in the z-domain; and

converting the zeros to the decay rate and the frequency.

6. The method of claim 5, wherein the filter is determined using a Prony'"'"'s method.

7. The method of claim 6, wherein the Prony'"'"'s method is solved using Singular Value Decomposition.

8. The method of claim 5, wherein the zeros for the filter are determined by a eigenvalue method.

9. The method of claim 5, wherein converting the zeros to the decay rate and the frequency includes sorting out noise zeros.

10. The method of claim 5, further comprising determining an amplitude for the time-varying signally collected in the substantially fluid state by harmonic data analysis of the decay rate and the frequency.

11. The method of claim 1, further comprising determining a resonance frequency for the time-varying signals collected in the substantially fluid state.

12. The method of claim 11, further comprising determining thickness, speed of sound, and density based on the resonance frequency.

13. The method of claim 11, wherein determining the resonance frequency includes modeling a propagation of ultrasound in the surface as a compressional wave traversing through the substantially fluid state of the surface.

14. The method of claim 1, wherein the calculated value is a thickness of the object in the substantially solid state.

15. The method of claim 14, wherein the thickness comprises:

calculating a thickness of the object in the substantially fluid state;

determining a prediction factor for a transition of the object from the substantially fluid state to the substantially solid state; and

calculating the thickness of the object in the substantially solid state based on the prediction factor and the thickness of the object in the substantially fluid state.

16. The method of claim 15, wherein determining the prediction factor comprises:

measuring impedance of the object in the substantially fluid state;

estimating percent solids of the object in the substantially fluid state; and

calculating the prediction factor based on the measured impedance and the estimated percent solids.

17. The method of claim 15, wherein determining the prediction factor is based on a physical model.

18. The method of claim 15, wherein determining the prediction factor is based on a calibration model.

19. The method of claim 1, wherein calculating the value for at least one substantially solid state property does not include an environmental calibration procedure.

20. The method of claim 1, further comprising:

determining a desired value for the calculated property;

comparing the calculated property value to the desired property value; and

producing a control signal that represents the comparison of the calculated valve to the desired value.

21. The method of claim 20 for a substrate and wherein the object is a coating, further comprising:

providing a robot having a controller and a means for applying the coating to the substrate, wherein the coating produces the surface that transitions from the substantially fluid state to the substantially solid state;

inputting the control signal to the robot; and

controlling the robot based on the control signal, wherein the application of the coating is controllable by the robot based on the control signal.

22. The method of claim 21, wherein the object and the robot are in an automotive assembly line.

23. The method of claim 21, further comprising:

inputting position signals to the robot relating to the position of the surface, wherein the robot is movable to the surface position in response to the position signal for further coating of the substrate.

24. The method of claim 21, further comprising:

producing motions in the surfaces of a plurality of objects having a surface that transitions from a substantially fluid state to a substantially solid state;

providing multiple robots having a controller and a means for applying a coating to each substrate, wherein the coating produces the surface that transitions from the substantially fluid state to the substantially solid state;

inputting multiple control signals responsive to each substrate to a computer; and

providing a system controller for receiving signals from the computer and selectively controlling each robot by producing individual control signals for each robot;

controlling each robot according to the individual control signals.

25. An apparatus for determining wet and dry properties of a surface of an object, the apparatus comprising:

laser means for producing surface motions in the object without touching the object and time-varying signals responsive to the surface motions;

a detection device for measuring the time-varying signals;

a processor for calculating at least one wet property of the surface based on the time-varying signals to predict a dry property value of the surface; and

a surface provider for providing an enhanced dry property value if the predicted dry property value is unacceptable.

26. A method of covering a substrate with a wet material dryable to an appearance finish of predetermined thickness without marring the appearance finish comprising:

covering the substrate with an initial coating of wet material to an unknown thickness;

exciting the initial coating thereon;

projecting a reflectable laser beam toward the initial coating;

receiving the reflection of the laser beam while the initial coating is still wet; and

converting the reflection to a measurement signal indicative of the thickness of the initial coating.

27. The method of claim 26, including covering the substrate with an additional coating of wet material while the initial coating is still wet and until the measurement signal indicates the appearance finish has the predetermined thickness.