Method and apparatus for measuring thickness of transparent films
First Claim
1. A method of measuring thickness of a film comprising:
- providing a single illumination beam propagating along an optical axis and illuminating the transparent film, the transparent film having a first and a second surface;
causing the illumination beam to reflect from the first surface of the transparent film, pass through a focusing means and form an image on an image capturing device, the image being characterized by a first image score;
altering a position of the transparent film along the optical axis relative to the focusing means, thereby altering the first image score until it reaches a second image score corresponding to an image being formed on the image capturing device by the illumination beam being reflected from the second surface of the transparent film; and
utilizing the first image score and the second image score to measure the thickness of the transparent film.
3 Assignments
0 Petitions
Accused Products
Abstract
A method and an apparatus for measuring thickness of transparent films is described in which an illumination beam is directed through an objective onto an object comprising a transparent film. A structured focusing aid is disposed in the illumination beam, a camera is disposed in an imaging beam. The focusing aid and the camera each are disposed in locations conjugated with the focal plane of the objective. The focal plane of the objective is displaced stepwise through the object. At each position, a camera image is recorded and its focus score is determined, the image of the focusing aid being used as the contrast indicator. The positions with maximal focus scores are assigned to the locations of the interfaces. The thickness of the transparent film is calculated from the difference between the positions of its interfaces.
-
Citations
13 Claims
-
1. A method of measuring thickness of a film comprising:
-
providing a single illumination beam propagating along an optical axis and illuminating the transparent film, the transparent film having a first and a second surface;
causing the illumination beam to reflect from the first surface of the transparent film, pass through a focusing means and form an image on an image capturing device, the image being characterized by a first image score;
altering a position of the transparent film along the optical axis relative to the focusing means, thereby altering the first image score until it reaches a second image score corresponding to an image being formed on the image capturing device by the illumination beam being reflected from the second surface of the transparent film; and
utilizing the first image score and the second image score to measure the thickness of the transparent film. - View Dependent Claims (2, 3, 4, 5)
-
-
6. A method for thickness measurement on transparent films, comprising the following steps:
-
a) illuminating an object, having a transparent film, by a single illumination beam that is guided through an objective which has an optical axis oriented perpendicular to the transparent film, a structured focusing aid being arranged in the illumination beam, and a camera being arranged in an imaging beam, in positions conjugated with the focal plane of the objective;
b) stepwise displacing the object relative to the objective in a Z direction, parallel to the optical axis, to discrete positions zi;
c) recording of a camera image at each stop position zi, and measuring an associated zi value;
d) identifying a focus score F(zi), assigned to the respective position zi, from each recorded camera image;
e) determining the maxima of the focus scores F(zi);
f) assigning the maxima to interfaces of the object; and
g) determining the thickness of the transparent film enclosed in the object from the difference between the two zi positions z1, Z2 of the maxima assigned to its interfaces, the thickness d of the transparent film being given by d=(z1−
z2)×
nfilm, where nfilm=the refractive index of the film.- View Dependent Claims (7, 8)
a) determining an approximating function F(z) from the discrete focus scores F(zi);
b) determining the analytical maxima of the function F(z); and
c) determining the thickness of the transparent film from the analytical maxima of the function F(z).
-
-
8. The method as defined in claim 6, comprises determining an approximation function F(z) in the vicinity of those discrete focus scores Fn(zi) whose adjacent focus scores Fn−
- m(zi) and Fn+m(zi) have lower values, the vicinity being defined as m≧
1.
- m(zi) and Fn+m(zi) have lower values, the vicinity being defined as m≧
-
9. An apparatus for carrying out the method for thickness measurement on transparent films, comprising:
-
a) an object that has a transparent film;
b) a light source;
c) an objective through which an illumination beam, proceeding from the light source and having an optical axis oriented perpendicular to the transparent film, is directed onto the object;
d) a structured focusing aid arranged in the illumination beam in a position conjugated with a focal plane of the objective;
e) a camera arranged in an imaging beam, defined by the apparatus, in a position conjugated with the focal plane of the objective;
f) a drive unit for displacing the object relative to the objective in a Z direction, parallel to the optical axis, to discrete positions zi;
g) a Z-position measurement unit for measuring the zi values of the zi positions stopped at;
h) an image recording unit connected to the camera;
i) an image processing unit for identifying a focus score F(zi), assigned to one of the respective positions zi, from each recorded camera image;
j) a calculation unit for evaluating the focus scores F(zi) and determining the thickness of the transparent film; and
k) a control unit, for controlling execution of the method, that is connected to the other units. - View Dependent Claims (10, 11, 12, 13)
-
Specification