Edge detecting apparatus having a control device which selectively operates the light emitting elements

An apparatus for detecting an edge of a surface of an object, comprising:

• at least three light emitting elements which are provided at respective different positions;
• a control device which selects, from said at least three light emitting elements,
• at least two operative light emitting elements providing at least two lighting devices, respectively;
• each one of said at least two lighting devices lighting, in a corresponding one of at least two different directions which are inclined relative to a normal of said surface of the object and have different angular phases about said normal, said surface of the object while the object is not rotated;
• an image taking device which takes an image of said surface of the object and a vicinity of said surface which are lighted by said each one of the lighting devices in said one of the different directions while the object is not rotated;
• the control device controlling the lighting devices and the image taking device such that said each one of the lighting devices lights said surface of the object in said one of the different directions and the image taking device takes the image of said surface of the object and the vicinity of said surface lighted by said each one lighting device in said one direction;
• and
• an image-data processing device which processes a plurality of batches of image data representing the respective images taken by the image taking device from said surface of the object lighted by said each one of the lighting devices in said one of the different directions, and detects an edge of said surface of the object.