Non-contact apparatus and method for measuring surface profile

Abstract

Embodiments of the invention provide a non-contact method for measuring the surface profile of an object that can include generating a point-type optical signal and projecting it on a rotatable precision optical grating, generating a rotating pattern of light and dark lines onto the object, recording a series of images of the rotating pattern moving across the object with an image receiving device and calculating the surface profile of the object. Other embodiments can include a method to calibrate the system and a non-contact apparatus that generally includes a point-type light source, a rotatably mounted optical grating being configured to project a moving grating image on the object, a processor in communication with the image capturing device and configured to receive image input from the image capturing device and generate a surface profile representation of the object therefrom.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a utility patent application that claims benefit of U.S. Provisional Patent Application Ser. No. 60 / 301,180, filed Jun. 27, 2001, which is hereby incorporated by reference in it's entirety.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention generally relates to the determination of surface profiles through optical-based methodologies and apparatus. [0004] 2. Description of the Related Art [0005] Accurate measurements of surface profiles are an important element in the inspection of manufactured parts, particularly when the inspection process is an automated process. Current inspection / surface profile measurement systems generally utilize coordinate measuring machines / devices, laser displacement gauges, and / or other similar methods. However, conventional methods are generally configured to measure only a single point at a time, and therefore, these systems are both time and resour...

AI Technical Summary

Benefits of technology

[0019] Embodiments of the invention further provide a non-contact method for measuring the surface profile of an object. The method may include generating a point-type optical signal, projecting the point-type optical signal on a rotatable precision optical grating. The method further includes generating a...

Problems solved by technology

However, conventional methods are generally configured to measure only a single point at a time, and therefore, these systems are both time and resource intensive.

Techniques such as Moiré Interferometry, Fourier Transform Profilometry, and other grid projection methods require that an entire image (or many entire images) of the surface be analyzed to measure the 3-dimensional position of even one point on the surface, which increases data acquisition and analysis time.

Moreover, if there is a discontinuous step in the surface, there will be a corresponding jump in the grid pattern and it may be impossible to uniquely identify gridlines across this discontinuity so that accurate measurements cannot be made.

Therefore, although these methods are appealing, the resources required to analyze the entire image surface in a 3-dimensional manner make these methods generally impracticable.

However, patterns from these types of techniques are generally difficult to interpret, and further, surface discontinuities in the object are known to result in ambiguous measurements when these techniques are employed.

Conventional structured light techniques generally require that the optical projection system and the camera system be placed in precise alignment, which causes difficulty if the system becomes misaligned, as can easily happen.

These precise processes and movements are expensive to generate, operationally slow, and very often require data collection for areas that are not of interest.

The simplicity of basic triangulation typically makes it the technique of choice for automated inspection systems, as the more complex techniques require calculations too lengthy for real-time application and usually involve a level of user interpretation of the data for all but the simplest surfaces.

Complex surfaces are also difficult to efficiently measure with automated 3-dimensional techniques.

Large surface discontinuities generally result in discontinuities in the grid pattern (or the “interference” pattern) that are almost impossible for machine vision systems to interpret autonomously, despite the use of complicated grid phase-shifting techniques and advanced fringe-processing algorithms.

Even in the case of triangulation, surfaces with sharp edges and large jumps between surface...

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