Optical observation device and method for observing articles at elevated temperatures

• US 6,859,285 B1
• Filed: 08/02/2000
• Issued: 02/22/2005
• Est. Priority Date: 08/31/1999
• Status: Expired due to Fees

• Current Assignee: OG Technologies, Inc.
• Original Assignee: OG Technologies, Inc.
• Inventors: Chang, Tzyy-Shuh
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): Barth, Vincent P.
• Application Number:
  US09/630,479
• Time in Patent Office: 1,665 Days
• Field of Search: 356/237.1, 356/237.2, 356/237.3, 356601-613, 250/330, 250/222.1, 110/185, 110/186, 431/10, 431/12, 431/13, 431/75, 382/152, 164/457
• US Class Current: 356/601
• CPC Class Codes: G01N 21/55 Specular reflectivity

Abstract

An optical system for viewing hot objects is disclosed. The system projects electromagnetic radiation to the part surface and detects the reflected portion. Based on wavelength and/or modulation of the applied illumination, the surface characteristics of the part can be observed without interference from self-emitted radiation.

Claims

1. An optical system for producing an image of the surface of an object, said object having a characteristic, temperature-dependent, dominant, self-emitted EMR spectrum, comprising:

an EMR source for projecting electromagnetic radiation toward said object;

an EMR detector for selectively detecting a spectrum component of said projected EMR, said component being reflected by the surface of said object and being directed toward said EMR detector;

an airflow controller to provide airflow at a preselected temperature around said hot object to decrease a temperature gradient to remove air density distortion; and

wherein said projected electromagnetic radiation has a wavelength which is selected as a function of object temperature and material, said reflected component of said projected EMR has said wavelength that is different than said self-emitted, dominant EMR spectrum such that the reflected component can be distinguished from said self-emitted EMR based on wavelength and wherein said optical system further includes an interference filter in association with said EMR detector configured to pass said wavelength and block self-emitted EMR.

2. An optical system as recited in claim 1, further including a frequency modulator in association with said EMR source for modulating the frequency of said projected EMR and further including a demodulator in association with said EMR detector.

3. A method of imaging the surface of a hot object having a characteristic, dominant, self-emitted electromagnetic radiation (EMR) spectrum comprising the steps of:

(A) defining a highest temperature, T, of the object during imaging;

(B) defining an object emissivity ε

(T, material) that is a function of the highest temperature T and material of the object;

(C) obtaining a self-emitted electromagnetic radiation spectrum R (λ

, T, material) based on a black body radiation function I(λ

, T), and the object emissivity ε

(T) in accordance with R(λ

, T, material)=ε

(T, material)·

I(λ

, T) wherein;

$I<br><br>\left(\mathrm{\lambda <br><br>},T\right)=\frac{2<br><br>\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>c^2<br><br>h}{{\mathrm{\lambda <br><br>}}^5}·<br><br>\frac{1}{{\mathrm{e<br><br>}}^{\mathrm{hc}/2<br><br>\mathrm{\kappa <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T}-1}$

 

and where

Π

=pi

C=light speed

h=Planck'"'"'s constant

λ

=wavelength

κ

=Boltzmann constant

ε

=emissivity function of temperature, empirically obtained,

(D) selecting a cut-off wavelength λ

cut-off such that the self-emitted electromagnetic radiation spectrum R(λ

_cut-off,T) is small compared to a signal intensity of an external, illuminating light η

(λ

_ill), in accordance with;

$\mathrm{\gamma <br><br>}=\frac{\mathrm{\eta <br><br>}<br><br>\left({\mathrm{\lambda <br><br>}}_{\mathrm{ill}}\right)}{R<br><br>\left({\mathrm{\lambda <br><br>}}_{\mathrm{cut}-\mathrm{off}},T\right)}\ge <br><br>{\mathrm{\gamma <br><br>}}_o$

 

where;

η

(λ

)=the intensity of the external illuminating light @ wavelength λ

γ

_ill=the wavelength used for external illumination

γ

=signal to noise ratio between the external illuminating light intensity and the self-emitted light intensity

γ

_o=specified signal to noise ratio limit that will satisfy the application

(E) determining the longest acceptable wavelength γ

_ill for the external illumination;

(F) projecting light with a wavelength less than or equal to γ

_ill toward the hot object;

(G) detecting the projected light as reflected from the hot object to thereby image the hot object.