# US 2013/0278756 A1 · Sensor for Simultaneous Measurement of Thickness and Lateral Position of a Transparent Object

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- Number: US 2013/0278756 A1
- Document ID: US20130278756A1
- Status: Published application
- Kind: A1
- Application number: 13/788,507
- Filed: 2013-03-07
- Published: 2013-10-24
- Earliest claimed: 2012-04-20
- Assignees: Massachusetts Institute of Technology
- Applicants: Massachusetts Institute of Technology
- Inventors: Dean Marko Ljubicic; Brian W. Anthony
- Web page: https://patentgrep.com/patent/US20130278756A1

## CPC

- G01C 11/02: Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures
- G01B 11/028: {by measuring lateral position of a boundary of the object (G01B11/022, G01B11/024, G01B11/04 take precedence)}
- G01B 11/06: for measuring thickness {; e.g. of sheet material (thickness measurement by thermal means G01B21/085)}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

System for measuring thickness and lateral position of a transparent object. The system includes a camera having a sensor for receiving light, the camera including an objective lens for focusing on an object plane and having an optical axis and a field of view. A source of light is provided to illuminate a surface having variations in reflected light intensity. The surface is spaced apart from the objective lens and disposed at an angle with respect to the optical axis of the objective lens. A transparent object disposed fully or partially between the objective lens and the surface will shift the position of the object plane, the shift in object plane being proportional to the thickness of the object, and the transparent object, when partially inserted between the objective lens and the surface, will focus a fraction of the light on a lower plane, this fraction of light being proportional to the fraction of the lens field of view occupied by the transparent object that is related to lateral position.

## Claims

### Claim 1

System for measuring thickness and lateral position of a transparent object comprising:
a camera including a sensor or for receiving light the camera including an objective lens for focusing on an object plane and having an optical axis and a field of view;
a source of light;
a surface having variations in reflected or transmitted light intensity spaced apart from the objective lens and illuminated by the source of light and disposed at an angle with respect to the optical axis of the objection lens;
whereby a transparent object disposed fully or partially between the objective lens and the surface will shift the position of the object plane, the shift in object plane being proportional to the thickness of the object, and the transparent object, when partially inserted between the object lens and the surface, will focus a fraction of the light on a second plane, this fraction of light being proportional to the fraction of the lens field of view occupied by the transparent object and related to lateral position.

### Claim 2 (depends on 1)

The system of claim 1 wherein the surface is a Ronchi grating.

### Claim 3 (depends on 2)

The system of claim 2 wherein the Ronchi grating has an alternating black and white striped pattern.

### Claim 4 (depends on 1)

The system of claim 1 further including computing apparatus running image processing algorithms operating on an output of the camera sensor to determine the location of the object plane.

### Claim 5 (depends on 4)

The image system of claim 4 wherein the algorithms, when a Ronchi grating column is in focus, will output high or low intensity values corresponding to white or black portions of the grating.

### Claim 6 (depends on 5)

The system of claim 5 wherein the algorithms use standard deviation of values in each grating column as a metric of focus.

### Claim 7 (depends on 4)

The system of claim 4 wherein the camera displays two separate peaks of reduced magnitude on a standard deviation plot, the relative magnitude of the two peaks determining lateral position of the object.