COMPUTER IMPLEMENTED METHOD OF RECOGNIZING A POSITION OF AN OBJECT

A method for position recognition, includes the steps of: picking up an image of an object having a circular arc shape as at least part of its profile, by an image pickup device; converting image information of the picked-up image in gray image data and storing the gray image data into a storage device; scanning the stored gray image with a profile scanning window composed of plural gray-level detection areas crossing an imaginary scanning circular profile corresponding to the shape on the gray image and arranged in circular along the scanning circular profile and using it to measure gray-level representative values of an inner- and outer-side gray-level detection areas inside and outside of the scanning circular profile; calculating, at each scanning position during scanning and for each detection area, an absolute value of a difference between the measured gray-level representative values of the inner- and outer-side gray-level detection areas; determining a number of such detection areas in which the absolute value of the difference is larger than a specified gray-level threshold value; detecting a position of the window where the calculated number of detection areas becomes a maximum with respect to their neighborhood, as a position of the shape of the object; and recognizing a position of the object from the detected position of the shape thereof.