Patent ID: 7078673
Filing Date: 2006-07-18
Classification: G06F

Abstract:
1. A method for measuring relative motion between an illuminated portion of a surface and an optical sensing device comprising a photodetector array including a plurality of rows and columns of pixels respectively aligned along first and second axes, said method comprising the steps of: a) detecting by means of said photodetector array a first light intensity pattern of said illuminated portion of the surface at a first point in time; b) comparing light intensity between neighbouring pixels of said photodetector array and determining along each of said first and second axes edge direction data from said detected first light intensity pattern, which edge direction data is descriptive of light intensity differences between said neighbouring pixels and includes: c) extracting edge inflection data from said edge direction data, said edge inflection data being descriptive of the succession of positive and negative edges along each of said first and second axes of said photodetector array and including: d) storing said edge inflection data extracted from said edge direction data; e) detecting a second light intensity pattern of said illuminated portion of the surface at a second point time; f) comparing light intensity between neighbouring pixels of said photodetector array and determining along each of said first and second axes said edge direction data from said detected second light intensity pattern; g) extracting edge inflection data from said edge direction data from said detected second light intensity pattern; wherein said step c) or g) further includes the steps of (α) counting a total number of said inflection conditions extracted at step c) or g) along at least one of said first and second axes; and (β) extracting inflection line data being descriptive of the succession of two adjacent edge inflection data of the same type transversal to said at least one of said first and second axes and including: (γ) counting a total number of line conditions transversal to said at least one axis; and wherein the method further comprises the step of: h) determining a measurement of the relative motion between said optical sensing device and said illuminated portion of the surface along said at least one axis based on a ratio of: (h1) a comparison of said edge inflection data extracted at steps c) and g) and (h2) a function of the counted total number of inflection conditions along said at least one determined axis and the total number of line conditions transversal to said at least one determined axis.