Scanning phase measuring method and system for an object at a vision station

Abstract

A method and system are provided including an optical head which moves relative to an object at a vision station to scan a projected pattern of imagable electromagnetic radiation across the surface of an object to be inspected at a relatively constant linear rate to generate an imagable electromagnetic radiation signal. In one embodiment, the electromagnetic radiation is light to develop dimensional information associated with the object. The optical head includes at least one projector which projects a grid of lines and an imaging subsystem which includes a trilinear array camera as a detector. The camera and the at least one projector are maintained in fixed relation to each other. Three linear detector elements of the array camera extend in a direction parallel with the grid of lines. The geometry of the optical head is arranged in such a way that each linear detector element picks up a different phase in the grid pattern. As the optical head is scanned across the surface of interest, the detector elements are continuously read out. Depth an each point on the surface is calculated from the intensity reading obtained from each of the detector elements that correspond to the same point on the surface. In this way, the phases of the pattern are calculated from the three intensity readings obtained for each point. In another embodiment, the imagable electromagnetic radiation is polarized and the response of the detector elements is polarization sensitive. The generated images are based on polarization for the surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is related to U.S. patent application entitled “Optical Measuring System” filed Jun. 17, 1994 and having U.S. Ser. No. 08 / 262,130.TECHNICAL FIELD[0002]This invention relates to non-invasive measuring methods and systems and, in particular, to scanning phase measuring methods and systems for an object at a vision station.BACKGROUND ART[0003]Height distribution of a surface can be obtained by projecting a light stripe pattern onto the surface and then reimaging the light pattern that appears on the surface. A powerful technique for extracting this information based on taking multiple images (3 or more) of the light pattern that appears on the surface while shifting the position (phase) of the projected light stripe pattern is referred to as phase shifting interferometry as disclosed in U.S. Pat. Nos. 4,641,972 and 4,212,073.[0004]The multiple images are usually taken using a CCD video camera with the images being digitized a...

AI Technical Summary

Benefits of technology

[0013]In carrying out the above objects and other objects of the present invention, a method is provided for high speed scanning phase measuring of an object at a vision station to develop physical information associated with the object. The method includes the steps of projecting a pattern of imagable electromagnetic radiation with at least one projector and moving the object relative to the at least one projector at the vision station to scan the projected pattern of electromagnetic radiation across a surface of the object to generate an imagable electromagnetic radiation signal. The method also includes the steps of receiving the imagable electromagnetic radiation signal from the surface of the object with a detector having a plurality of separate detector elements and maintaining the at least one projector and the detector in fixed relation to each other. Finally, the method includes the steps of measuring an amount of radiant energy in the received electromagnetic radiation signal wherein the detector elements produce images having different phases of the same scanned surface based on the measurement and computing phase values and amplitude values for the different phases from the images.

Problems solved by technology

A technique for capturing just one bucket image using a line scan camera is described in U.S. Pat. No. 4,965,665 but not enough information is available to do a phase calculation based on multiple buckets.

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