Patent ID: 8823952

Claim:
A measurement method for determining at least one of the group consisting of position and displacement of a mobile element with respect to a fixed frame, wherein a fixed light source ( 1 ) emitting a light beam is used, the light source ( 1 ) is arranged with respect to the mobile element and with respect to a sensor ( 2 ) in a way so as to induce an interaction between the light beam and the sensor ( 2 ) which depends on the position of the mobile element and wherein processing and computing means are used for providing a value of the at least one of the group consisting of the position and the displacement of the mobile element in dependence of the output signal of the sensor ( 2 ), said measurement method comprising the steps of: a) using a concave mirror ( 3 ), fixed to the mobile element, for reflecting the light beam in direction to the sensor ( 2 ), b) arranging on the path of the light beam a fixed optical mask ( 4 ) which comprises a two dimensional regular pattern, c) detecting and processing a displacing image casted by the optical mask ( 4 ) on the sensor ( 2 ), d) computing the displacement value of said displacing image on said sensor ( 2 ), and e) using the computed displacement value for computing and providing the at least one of the group consisting of the position and the displacement in at least one direction of the mobile element in dependence of displacing image's displacement.