Patent ID: 6055329
Filing Date: 2000-04-25
Classification: G01B

Abstract:
An apparatus for determining deviation of characteristics of a sample workpiece from characteristics of a control workpiece, comprising:an illumination system for producing a collimated beam having substantially parallel rays;a positioning system for placing the sample workpiece between outer edges of said collimated beam to produce a sample image including a silhouette of the sample workpiece;an imaging array, normal to said collimated beam and comprising a plurality of discrete light sensing elements, for producing signals corresponding to intensities of pixels of said sample image including said silhouette; anda processor for producing pixel data corresponding to said signals and for determining dimensions of the sample workpiece by:determining a diffraction band produced by edges of said sample workpiece and having an intensity of a diffraction band of a control image produced by edges of a control workpiece of the same type as the sample workpiece;determining a sample distance between points located within said diffraction band of said sample image;determining a control distance between corresponding points located within the diffraction band of the control image;determining an offset between said control distance and a known distance between corresponding points of the control workpiece; andapplying the offset to said sample distance.