Spectroscopic sensor for thickness or weight measurement of thin plastic films

Patent metadata

Field	Value
Publication number	US-9927366-B2
Application number	US-201514667607-A
Country	US
Kind code	B2
Filing date	Mar 24, 2015
Priority date	Mar 24, 2015
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

Continuous on-line thin film measurements employ a sensor having a spectrometer for interferometric measurements and a stack of single channel detectors for adsorption measurements. The stack is separated from the spectrometer, which analyzes radiation that emerges (transmitted pass or reflected from) the film, whereas the stack analyzes radiation that has passed through the film multiple times. The spectrometer is (i) positioned directly opposite the source of radiation so that it detects transmitted radiation or (ii) disposed on the same side of the film as is the source of radiation so that the spectrometer detects radiation that is specularly reflected from the film. The sensor includes a broadband radiation source emitting visible to far infrared light which propagates through a measurement cell defined by reflective surfaces exhibiting Lambertian-type scattering. The sensor is capable of measuring thin plastic films with thicknesses down to 1 micron or less.

First claim

What is claimed is:

1. An apparatus for sensing a layer of plastic material that comprises:
a radiation source, disposed on a first side of the layer of plastic material, that directs a beam of incident radiation into the layer of plastic material wherein the radiation source emits broadband radiation from the visible to the far infrared region;
a spectrometer, configured to detect interference, that detects transmitted broadband radiation that passes through the layer of plastic material;
a radiation receiver that detects at least a portion of a reflected beam of broadband that propagates through the layer of material wherein the radiation receiver comprises at least one of a plurality of single channel detectors, wherein the spectrometer analyzes broadband radiation in a first radiation range and the radiation receiver analyzes broadband radiation in a second radiation range wherein a spectrum characteristic of the spectrometer and a spectrum characteristic of all of said plurality of channel detectors do not overlap and wherein the spectrometer and the radiation receiver operate simultaneously: and
one or more members with reflective surfaces that define a measurement cell with a path for the layer of plastic material and wherein the measurement cell is configured to cause broadband radiation to be reflected through the layer of material a plurality of times before being detected by the radiation receiver wherein the reflected broadband radiation propagating through the measurement cell exhibit Lambertian-type scattering.

2. The apparatus of claim 1 wherein the spectrometer, which is disposed on a second side of the layer of plastic material and opposite the radiation source.

3. The apparatus of claim 1 wherein the pair of members includes a first member that has a first plate and a second member that includes a second plate, wherein the first and second plates are substantially parallel and the plates are positioned on opposite sides and substantially parallel to the layer of plastic material, wherein the first plate has a first aperture that is coupled to the radiation source and wherein the second plate has a second aperture that is coupled to the radiation receiver.

4. The apparatus of claim 1 wherein the pair of members includes a first member that has a first plate and a second member that includes a second plate, wherein the first plate and second plate are substantially parallel and the plates are positioned on the opposite sides and substantially parallel to the layer of plastic material, wherein the first plate has a first aperture that is coupled to the radiation source and wherein the first plate has a second aperture that is coupled to the radiation receiver.

5. The apparatus of claim 1 wherein the spectrometer is one of in a visible spectral range, in a near infrared spectral range, in a mid-infrared spectral range, and in a far infrared spectral range.

6. The apparatus of claim 1 comprising a pair of members that defines a measurement cell for the layer of plastic material, wherein the radiation source and radiation receiver have respective axes of radiation and detection that are laterally offset from one another with respect to the path.

7. The apparatus of claim 1 the radiation receiver comprising:
a plurality of beam splitters for splitting the reflected beam radiation;
a plurality of bandpass filters for filtering the reflected beam radiation; and
a plurality of single channel detectors, each channel detector being coupled to one bandpass filter with each coupled channel detector and bandpass filter measures one or more characteristics of said plurality of characteristics of the layer of plastic material using said split radiation received from one or more of said plurality beam splitters, said characteristics measured by each coupled channel detector and bandpass filter being different from the characteristics measured by the spectrometer.

8. The apparatus of claim 1 wherein each member includes a diffuser, facing a side of the layer of material, that comprises of (i) at least one layer of material that comprises calcium fluoride, sapphire, quartz glass and/or alumina that is formed on a specular reflective surface or (ii) a diffusively reflective surface comprising metallic layer with a rough surface, wherein the measurement cell is configured to cause broadband radiation to be reflected through the layer of plastic material a plurality of times before being detected by the radiation receiver.

9. The apparatus of claim 1 wherein each member includes a diffuser, facing a side of the layer of plastic material, that comprises a reflective surface securing a layer of PTFE, which is covered by quartz glass.

10. A method for measuring a plurality of characteristics of a flat sheet of plastic which comprises:
(a) emitting broadband radiation towards the flat sheet of plastic;
(b) analyzing reflected broadband radiation, with a radiation receiver which comprises at least one of a plurality of single channel detectors, that has propagated through the flat sheet of plastic a plurality of times to measure characteristics using adsorption techniques by propagating the reflected broadband radiation through a measurement cell defined by reflective surfaces exhibiting Lambertian-type scattering; and
(c) analyzing transmitted broadband radiation that passes through the flat sheet of plastic with a spectrometer when interference is detected wherein the spectrometer analyzes broadband radiation in a first radiation range and the radiation receiver analyzes broadband radiation in a second radiation range wherein a spectrum characteristic of the spectrometer and a spectrum characteristic of all of said plurality of channel detectors do not overlap and wherein steps (b) and (c) are performed simultaneously to generate a thickness profile.

11. The method of claim 10 wherein step (a) emits broadband radiation that ranges from visible to far infrared.

12. The method of claim 10 wherein flat sheet of plastic comprises polymeric film.

13. An apparatus for sensing a layer of plastic material that comprises:
a radiation source, disposed on a first side of the layer of plastic material, that directs a beam of incident radiation into the layer of plastic material wherein the radiation source emits broadband radiation from the visible to the far infrared region;
a spectrometer, configured to detect interference, which is disposed on the second side of the layer of plastic material and opposite the radiation source, and that detects transmitted broadband radiation in the visible or near-infrared spectra range that passes through the layer of plastic material wherein the spectrometer analyzes broadband radiation in a first radiation range;
a radiation receiver that detects at least a portion of a reflected beam of broadband radiation that propagates through the layer of plastic material where the radiation receiver analyzes broadband radiation in a second radiation range, wherein the radiation receiver comprises at least one of a plurality of single channel detectors and wherein a spectrum characteristic of the spectrometer and a spectrum characteristic of all of said plurality of single channel detectors do not overlap; and
one or more members with reflective surfaces that define a measurement cell with a path for the layer of plastic material and wherein the measurement cell is configured to cause broadband radiation to be reflected through the layer of plastic material a plurality of times before being detected by the radiation receiver wherein the reflected radiation propagating through the measurement cell exhibit Lambertian-type scattering.

Assignees

• Tixier Sebastien
• Haran Frank Martin
• Honeywell Ltd

Inventors

• Tixier Sebastien
• Haran Frank Martin

Classifications

• G01N2201/068

  Optics, miscellaneous · CPC title

• G01N2021/8609

  Optical head specially adapted · CPC title

• G01N21/3563

  for analysing solids; Preparation of samples therefor · CPC title

• G01N21/8422 Primary

  Investigating thin films, e.g. matrix isolation method · CPC title

• G01G9/00

  Methods of, or apparatus for, the determination of weight, not provided for in groups G01G1/00 - G01G7/00 · CPC title