Patent ID: 8391561

Claim:
A tension monitoring system, comprising: a washer, being part of a fastener securing a first object in relation to a second object, said washer being provided with at least one pattern located on a surface of said washer and where the pattern comprises pattern portions arranged relative to each other with a distance between pattern portions on a distance scale suitable for detecting tension within a predetermined range and resolution, wherein the pattern portions each comprise a plurality of points and where each point is arranged fixedly on the washer; at least one camera for acquiring at least one image of the at least one pattern located on the washer; a computational device arranged to receive image information from the at least one camera; wherein the computational device is arranged to analyze the acquired image for detecting the position of each point using an image analysis algorithm arranged to determine the geometrical centre of a point using a contrast detection method, determining the distance between at least two pattern portions, and calculating the tension induced in the washer using a reference value of distance between the two pattern portions when the washer is mechanically relaxed.