Method and apparatus for optically inspecting a mold for manufacturing ophthalmic lenses for possible mold defects

Patent metadata

Field	Value
Publication number	US-10867379-B2
Application number	US-201916538446-A
Country	US
Kind code	B2
Filing date	Aug 12, 2019
Priority date	Aug 13, 2018
Publication date	Dec 15, 2020
Grant date	Dec 15, 2020

Abstract

A method for optically inspecting a mold (10) for manufacturing ophthalmic lenses such as contact lenses for possible mold defects, including: generating a set of images of the mold (10) for different azimuthal illumination angles (ϕ1, ϕ9) using an illumination system (20) and an imaging system (30), the latter being aligned such that its focal plane cuts through the mold (10) at a specific axial position along a center axis of the mold (10); generating a focal plane image by averaging pixelwise over the set of images after having masked out in each image those regions that include direct specular reflections from the mold (10); repeating the previous steps for one or a plurality of different axial positions of the focal plane such as to generate a plurality of different focal plane images; identifying one or more image features in the plurality of focal plane images indicative for a possible mold defect; determining for each identified image feature in which focal plane image the identified image feature appears sharpest; generating for each identified image feature a respective image section out of the respective sharpest focal plane containing the image feature; and generating a composed dark field image of the mold (10) by composing the respective image sections for each identified image feature, thus enabling to determine as to whether the possible defects of the mold (10) still allow the mold (10) to be used.

First claim

The invention claimed is:

1. A method for optically inspecting a mold ( 10 ) for manufacturing ophthalmic lenses for possible mold defects, the method comprising the steps of:
a. taking an image ( 41 ) of the mold ( 10 ) along a center axis (Z) of the mold ( 10 ) that extends through an apex ( 15 ) of the mold and normal to a mold surface ( 16 ) at the apex ( 15 ) by
illuminating the mold ( 10 ) with light ( 26 ) incident at an azimuthal illumination angle (ϕ 1 ) and a polar illumination angle (Θ) with regard to the center axis (Z), and
collecting and detecting light ( 28 ) reflected or scattered, respectively, from the mold ( 10 ) using an imaging system ( 30 ) arranged along and aligned with the center axis (Z), wherein a focal plane ( 31 ) of the imaging system ( 30 ) has an axial position (z 1 ) along the center axis (Z) in the range of the mold ( 10 );

b. repeating step a. for one or a plurality of different azimuthal illumination angles (ϕ 2 , ϕ 3 , ϕ 4 , ϕ 5 ) around the center axis (Z) at the same polar illumination angle (Θ) and the same axial position (z 1 ) of the focal plane ( 31 ) to generate a plurality of images ( 41 , 42 , 43 , 44 , 45 ) of the mold;
c. generating a masked dark field image ( 54 ) for each image of the plurality of images ( 41 , 42 , 43 , 44 , 45 ) taken at the different azimuthal illumination angles (ϕ 1 , ϕ 2 , ϕ 3 , ϕ 4 , ϕ 5 ) at the same axial position (z 1 ) of the focal plane ( 31 ) by applying a respective specular reflection mask ( 40 ) to each image of the plurality of images ( 41 , 42 , 43 , 44 , 45 ) of the mold such as to mask out image regions ( 44 a , 44 b ) that include direct specular reflections ( 23 , 24 ) from the mold ( 10 ), so as to obtain a plurality of masked dark field images;
d. generating a focal plane image ( 61 ) for the axial position (z 1 ) of the focal plane ( 31 ) by averaging pixelwise over the masked dark field images ( 54 ) generated at the different azimuthal illumination angles (ϕ 1 , ϕ 2 , ϕ 3 , ϕ 4 , ϕ 5 ) at the same axial position (z 1 ) of the focal plane ( 31 );
e. repeating steps a. to d. for one or a plurality of different axial positions (z 2 , z 3 ) of the focal plane ( 31 ) to generate a plurality of different focal plane images ( 61 , 62 , 63 );
f. identifying one or more image features ( 71 , 72 , 73 , 74 ) in the plurality of different focal plane images ( 61 , 62 , 63 ), each image feature ( 71 , 72 , 73 , 74 ) showing a possible mold defect;
g. determining for each identified image feature ( 71 , 72 , 73 , 74 ) a respective sharpest focal plane image ( 61 , 62 , 63 ) of the plurality of different focal plane images ( 61 , 62 , 63 ) by determining for which focal plane image ( 61 , 62 , 63 ) of the plurality of different focal plane images ( 61 , 62 , 63 ) a pre-defined sharpness measure of the identified image feature ( 71 , 72 , 73 , 74 ) is at a maximum;
h. generating for each identified image feature ( 71 , 72 , 73 , 74 ) a respective image section ( 81 , 82 , 83 , 84 ) out of the respective sharpest focal plane image ( 61 , 62 , 63 ), wherein the identified image section ( 81 , 82 , 83 , 84 ) includes the identified image feature ( 71 , 72 , 73 , 74 );
i. generating a composed dark field image ( 90 ) of the mold ( 10 ) by composing the respective image sections ( 81 , 82 , 83 , 84 ) for each identified image feature ( 71 , 72 , 73 , 74 ) such as to enable determination as to whether the possible defects of the mold ( 10 ) allow the mold ( 10 ) to be used for manufacturing ophthalmic lenses.

2. The method according to claim 1 , wherein the step of identifying one or more image features ( 71 , 72 , 73 , 74 ) in the plurality of different focal plane images ( 61 , 62 , 63 ) includes
defining a pixel value threshold between background and non-background image data;
generating a binary identification image of the same size as that of the plurality of different focal plane images ( 61 , 62 , 63 ) by setting a respective pixel of the binary identification image to a first value if a pixel value of a corresponding pixel of at least one of the focal plane images ( 61 , 62 , 63 ) is above the pixel value threshold, and by setting a respective pixel of the binary identification image to a second value if a pixel value of a corresponding pixel of all focal plane images ( 61 , 62 , 63 ) is below the pixel value threshold;
identifying in the binary identification image one or more pixel patterns consisting of a singular pixel or a plurality of connected pixels set to the first value;
determining for each focal plane image ( 61 , 62 , 63 ) and each identified pixel pattern of the binary identification image whether one or more pixels of the focal plane image ( 61 , 62 , 63 ) within a respective image portion corresponding to a respective one of the identified pixel patterns ( 172 ) of the binary identification image have a pixel value that is above the pixel value threshold, and identifying the possibly determined one or more pixels in the focal plane image ( 61 , 62 , 63 ) as an image feature ( 71 , 72 , 73 , 74 ) showing a possible mold defect.

3. The method according to claim 1 , wherein the step of identifying one or more image features ( 71 , 72 , 73 , 74 ) further includes defining for each identified image feature ( 71 , 72 , 73 , 74 ) a respective region of interest around the identified image feature ( 71 , 72 , 73 , 74 ) such that the identified image feature ( 71 , 72 , 73 , 74 ), in particular a corresponding pixel pattern ( 172 ) identified in the binary identification image, is included in the region of interest at least for each focal plane image ( 61 , 62 , 63 ) showing the identified image feature.

4. The method according to claim 2 , wherein the step of identifying one or more image features ( 71 , 72 , 73 , 74 ) further includes defining for each identified image feature ( 71 , 72 , 73 , 74 ) a respective region of interest around the identified image feature ( 71 , 72 , 73 , 74 ) such that the identified image feature ( 71 , 72 , 73 , 74 ), in particular a corresponding pixel pattern ( 172 ) identified in the binary identification image, is included in the region of interest at least for each focal plane image ( 61 , 62 , 63 ) showing the identified image feature.

5. The method according to claim 3 , wherein the pre-defined sharpness measure of each identified image feature ( 71 , 72 , 73 , 74 ) is determined within the respective region of interest only.

6. The method according to claim 3 , wherein for each identified image feature ( 71 , 72 , 73 , 74 ) the respective image section ( 81 , 82 , 83 , 84 ) of the respective sharpest focal plane image ( 61 , 62 , 63 ) corresponds to the respective region of interest.

7. The method according to claim 1 , wherein the step of generating a focal plane image ( 61 , 62 , 63 ) includes applying a depth-of-field mask after averaging over the masked dark field images ( 54 ) such as to mask out non-sharp image regions showing mold portions which are outside a focal range of the imaging system ( 30 ) at the respective axial position (z 1 , z 2 , z 3 ) of the focal plane ( 31 ).

8. The method according to claim 1 , wherein step b. includes repeating step a. such as to take at least three images ( 41 , 42 , 43 , 44 , 45 ) of the mold ( 10 ) corresponding to at least three azimuthal illumination angles (ϕ 1 , ϕ 2 , ϕ 3 , ϕ 4 , ϕ 5 ), which are angularly equidistantly distributed around the center axis (Z).

9. The method according to claim 1 , wherein step b. includes repeating step a. such as to take at least ten images ( 41 , 42 , 43 , 44 , 45 ) of the mold ( 10 ) corresponding to

Assignees

• Alcon Inc

Inventors

• Etzold Fabian
• Warken Arno Florian
• Kiefhaber Daniel
• Campanelli Giovanni

Classifications

• G01N21/8806 Primary

  Specially adapted optical and illumination features · CPC title

• G06T7/0002 Primary

  Inspection of images, e.g. flaw detection · CPC title

• H04N23/56

  provided with illuminating means · CPC title

• G06T2207/10148

  Varying focus · CPC title

• G06T2207/10152

  Varying illumination · CPC title