System and method for determining at least one parameter relating to an angular movement of an arbor comprising a rotating reflector with contigous oblique chamfers

A system (6) for determining at least one parameter relating to an angular movement of an arbor (4), particularly a stem (4) integral with a timepiece (1) crown (2), the system (6) comprising:

• an arbor (4) configured to be able to rotate on itself around a longitudinal direction (D1);
• a rotating reflector (8) mounted on the arbor (4), around said arbor (4)
• two emitter/detector pairs (10A, 10B), the two pairs (10A, 10B) being disposed on either side of the rotating reflector (8), facing the reflector (8), each emitter/detector pair (10A, 10B) comprising a light source (16) intended to illuminate one part of the reflector (8), and a light detector (18) intended to receive a reflected light beam (24) from the reflector (8) and to generate an electrical signal (26A, 26B) representative of said beam (24);
• and
• a processor configured to process each of the electrical signals generated by the detectors (18), and to determine, as a function of the processing result, said at least one parameter relating to the angular movement of the arbor (4);
• characterized in that the rotating reflector (8) is formed from a cylinder of revolution, on the edges of which are arranged several contiguous, oblique chamfers (14), the outer surface (12) of the non-chamfered part of the reflector (8) seen from each emitter/detector pair (10A, 10B) forming an active reflective portion of the reflector (8) for said pair, which changes when the reflector (8) rotates on itself, such that the representative electrical signal (26A, 26B) generated by said detector (18) of the pair (10A, 10B) has a substantially sinusoidal shape when the reflector (8) rotates on itself in a regular manner in a same direction of rotation (S1, S2).