Sensor for simultaneous measurement of thickness and lateral position of a transparent object
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.
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.
2. The system of claim 1 wherein the surface is a Ronchi grating.
3. The system of claim 2 wherein the Ronchi grating has an alternating black and white striped pattern.
4. 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.
5. 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.
6. The system of claim 5 wherein the algorithms use standard deviation of values in each grating column as a metric of focus.
7. 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.