Non-invasive thickness measurement using capacitance measurement

• US 10,209,054 B2
• Filed: 04/20/2016
• Issued: 02/19/2019
• Est. Priority Date: 04/20/2016
• Status: Active Grant

• Current Assignee: Duke University
• Original Assignee: Duke University
• Inventors: Andrews, Joseph Batton, Brooke, Martin, Franklin, Aaron D.
• Primary Examiner(s): Shah, Neel
• Application Number:
  US15/133,727
• Publication Number:
  US 20170307349A1
• Time in Patent Office: 1,035 Days
• CPC Class Codes: B60C 11/243 Tread wear sensors, e.g. electronic sensors
• CPC Class Codes: B60C 2011/0033 Thickness of the tread
• CPC Class Codes: B60C 2019/004 Tyre sensors other than for detecting tyre pressure
• CPC Class Codes: B60C 9/0007 Reinforcements made of metallic elements, e.g. cords, yarns, filaments or fibres made from metal
• CPC Class Codes: B60C 9/2006 consisting of steel cord plies only
• CPC Class Codes: G01B 7/08 using capacitive means
• CPC Class Codes: G01M 17/02 Tyres

Abstract

Methods of measuring thickness of a material using cross-capacitance. The method generally includes applying a time-varying signal to a first pad and monitoring a response of a capacitor formed by the first pad, a spaced apart second pad, and the material. The pads may be permanently affixed to the material, in spaced relation to each other. Based on the response, a capacitance of the capacitor is determined. The material may be homogenous or heterogeneous, and has dielectric properties. Because the material acts as a dielectric, the capacitance of the capacitor changes as the thickness of the material changes. Thus, the thickness of the material may be determined based on the determined capacitance. The method may be advantageously employed to measure the thickness of a vehicle tire or other material. Related apparatuses are also disclosed.

Claims

1. A method of determining a thickness of a vehicle tire, the method comprising:

applying a time-varying signal to a first electrically conductive pad;

wherein the first pad is disposed in spaced relation to a second electrically conductive pad and electrically isolated therefrom;

wherein the second pad is grounded;

wherein the first and second pads are permanently affixed to the vehicle tire;

wherein the first pad, the second pad, and the vehicle tire jointly form a capacitor;

determining a capacitance of the capacitor based on an electrical response of the capacitor to the application of the time-varying signal to the first pad;

determining the thickness of the vehicle tire based on the determined capacitance;

wherein the time-varying signal is an oscillating signal;

wherein the vehicle tire has first and second generally oppositely disposed surfaces;

wherein the first and second pads are permanently affixed to the first surface;

wherein the first surface is an inner surface of the vehicle tire;

wherein the vehicle tire comprises a steel reinforcing mesh embedded in a dielectric material;

wherein the determined thickness includes the thickness of the combined steel reinforcing mesh and the dielectric material;

wherein the determining the capacitance comprises controlling a timing circuit based on the electrical response of the capacitor, and counting an output of the timing circuit to determine a frequency, and determining the capacitance based on the frequency.

2. The method of claim 1, wherein the first pad and the second pad are disposed substantially parallel to each other.

3. The method of claim 1, wherein the vehicle tire has a plurality of recesses on a surface thereof disposed opposite the first and second pads.

4. The method of claim 1, wherein the first and second pads are spaced from each other by about 0.15 mm.

5. A method of determining a thickness of a vehicle tire between first and second generally oppositely disposed surfaces, the method comprising:

applying a time-varying signal to a first electrically conductive pad;

wherein the first pad is disposed in spaced relation to a second electrically conductive pad and electrically isolated therefrom;

wherein the second pad is grounded;

wherein the first pad, the second pad, and the vehicle tire jointly form a capacitor;

wherein the second surface of the vehicle tire comprises a plurality of recesses therein;

wherein the vehicle tire is a heterogeneous material comprising a first metallic component embedded in a second dielectric component, wherein the first and second components are distinct from each other;

determining a capacitance of the capacitor based on an electrical response of the capacitor to the application of the time-varying signal to the first pad;

determining the thickness of the vehicle tire based on the determined capacitance;

wherein the time-varying signal is an oscillating signal;

wherein the first and second pads are permanently affixed to the first surface;

wherein the first surface is an inner surface of the vehicle tire;

wherein the determined thickness includes the thickness of the combined first metallic component and the second dielectric material;

wherein the determining the capacitance comprises controlling a timing circuit based on the electrical response of the capacitor, and counting an output of the timing circuit to determine a frequency, and determining the capacitance based on the frequency.

6. The method of claim 5, wherein the first pad and the second pad are disposed substantially parallel to each other.

7. A tire assembly, comprising:

a tire comprising a dielectric material and a metal material embedded therein;

the tire having an inner surface and an exterior surface disposed generally opposite to the inner surface;

a first electrically conductive pad;

a second electrically conductive pad;

wherein the second pad is grounded;

wherein the first and second pads are permanently affixed to the interior surface of the material;

wherein the first pad is disposed in spaced relation to a second pad and electrically isolated therefrom;

wherein the first pad, the second pad, and the material jointly form a capacitor;

a processing circuit communicatively connected to the first and second pads and configured to;

apply a time-varying signal to a first pad;

determine a capacitance of the capacitor based on an electrical response of the capacitor to the application of the time-varying signal to the first pad;

determine a thickness of the material based on the determined capacitance;

wherein the determining the capacitance comprises controlling a timing circuit based on the electrical response of the capacitor, and counting an output of the timing circuit to determine a frequency, and determining the capacitance based on the frequency.

8. The tire assembly of claim 7, wherein the exterior surface of the tire comprises a plurality of recesses.

9. The tire assembly of claim 7, wherein the first and second pads are disposed substantially parallel to each other.

10. The tire assembly of claim 7, wherein the processing circuit is configured to determine the local thickness based on the capacitance by consulting a lookup table of reference values.

11. The tire assembly of claim 7, wherein the processing circuit is mounted to the tire.

12. The tire assembly of claim 7:

wherein the first pad and the second pad comprise a first sensor assembly;

further comprising a second sensor assembly disposed in spaced relation to the first sensor assembly;

the second sensor assembly configured to determine a local thickness of the tire at a location spaced from the first sensor assembly.