US 11,255,659 B2Granted

Thickness determination of web product by mid-infrared wavelength scanning interferometry

AssigneeHoneywell ASCa Inc.

InventorsMichael Kon Yew Hughes, Sebastien Tixier, Stephane Savard

Life of this patent

Estimating the term…

Loading patent…

Abstract

Non-contacting caliper measurements of free-standing sheets detect mid-IR interferometric fringes created by the reflection of light from the top and bottom surfaces of the sheet. The technique includes directing a laser beam at a selected angle of incidence onto a single spot on the exposed outer surface and scanning the laser beam through a selected wavelength range as the laser beam is directed onto the exposed outer surface and measuring the intensity of an interference pattern that forms from the superposition of radiation that is reflected from the exposed outer surface and from the inner surface. Alternatively, the intensity of an interference pattern formed from the superposition of radiation that is directly transmitted through the web and radiation that is transmitted through the web after internal reflections from the internal surfaces of the web. Thickness can be extracted from the fringe separation in the interference pattern.

Claims16

Dependent claims

A non-contact method of measuring the thickness of a moving film, which has a first side and a second side, that comprises:

a. supporting the moving film wherein the film has an outer surface on the first side and an inner surface on the second side;
b. directing a laser beam from a tunable quantum cascade laser at a selected set angle of incidence onto a single spot on the outer surface on the first side, wherein the laser beam is tuned across a mid-infrared range of wavelengths that is between 8-25 microns;
c. scanning the laser beam wavelength through a selected range that is within the mid-infrared range;
d. measuring the intensity of an interference pattern with a detector wherein the interference pattern forms from superposition of radiation that is transmitted directly through the film and radiation that is transmitted through the second side after internal reflections within the film;
e. generating, synchronized wavelength signals, using a wavelength scan controller, that are communicated to the laser and a computer,
f. correlating with the computer the measurement signals from the detector with the wavelength of the laser beam as the laser beam wavelengths are scanned through the selected mid-infrared range;
and
g. calculating the thickness of the film by analyzing the interference pattern of the film by utilizing the relationship among the laser beam incident angle (⊖1), wavelength (λ0), index of refraction of the film (n2), and film thickness (d) wherein said relationship is expressed as
n
1
2
⁢
⁢
sin
2
⁢
⁢
θ
1
=
n
2
2
-
(
m
⁢
⁢
λ
0
2
⁢
d
)
2
,
wherein m is the interference order and is an integer, m=0, 1, 2, . . . and (n1) is the index of refraction of air.

34 more elements

A system for thickness measurements of a moving sheet of material having a first side and a second side that comprises:

(a) a first scanning head disposed adjacent to the first side of the moving sheet wherein the first scanning head has a first operative face and an infrared radiation source comprising at least one tunable quantum cascade laser that is configured to direct a laser beam of radiation that has a wavelength that is scanned through a selected range between 8-25 microns;
(b) a second scanning head disposed adjacent the second side of the moving sheet wherein the second scanning head has a second operative face, wherein the first operative face and the second operative face define a measurement gap though which the moving sheet travels without contacting the first or second operative faces;
(c) a detector positioned in the second scanning head, the detector is configured to detect the intensity of an interference pattern that forms from superposition of radiation that is transmitted directly through the moving sheet and radiation that is transmitted through the second side of the moving sheet after internal reflections within the moving sheet;
(d) a computer that is configured to correlate measurement signals from the detector with the mid-infrared range of wavelengths generated by the tunable quantum cascade laser beam as the laser beam wavelengths are scanned through the selected mid-infrared range;
(e) a wavelength scan controller configured to generate synchronized wavelength signals that are communicated to the tunable quantum cascade laser and;
and
(f) a microprocessor that is configured to the interference pattern and that is configured to calculate the thickness of the sheet wherein the thickness of the sheet (d) is related to laser beam incident angle (θ1), wavelength (λ0), and index of refraction of the sheet (n2), by a relationship which is expressed as
n
1
2
⁢
⁢
sin
2
⁢
⁢
θ
1
=
n
2
2
-
(
m
⁢
⁢
λ
0
2
⁢
d
)
2
,
wherein m is the interference order and is an integer, m=0, 1, 2, . . . and (n1) is the index of refraction of air.

33 more elements

Dependencies are inferred from the claim text.

Facts

Application: 15/900,192Filed 20 Feb 2018 · division
Priority: 4 Mar 2014
Published: US 2018/0172432 A121 Jun 2018
Granted: 22 Feb 2022
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

G01B 11/0675
Of coating: using interferometry
G01B 9/02017
Characterised by the beam path configuration: with multiple interactions between the target object and light beams, e.g. beam reflections…
G01B 11/0691
For measuring thickness ; e.g. of sheet material: of objects while moving
G01B 11/0625
Of coating: with measurement of absorption or reflection