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The present invention relates to a method for measuring the angular position of a contrasting edge of an object having a luminance transition zone which is substantially rectilinear in a given direction and separates two regions of different luminances. This method comprises the functional steps of:

The present invention relates to a method for measuring the angular position of a contrasting edge of an object having a luminance transition zone which is substantially rectilinear in a given direction and separates two regions of different luminances. This method comprises the functional steps of: —carrying out, in a transverse direction different from the given direction, an amplitude modulation of the signals delivered by a first and a second optical sensor; and —calculating an output signal (Yout(t)) starting from the signals delivered by the first and the second optical sensors (D1, D2) as a function of the angular position of the luminance transition zone. Device and set of devices for measuring the angular position of a contrasting edge and steering aid system for fixation and tracking a target comprising at least one such contrasting edge.

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1. A method for measuring the angular position of a contrasting edge of an object having a luminance transition zone which is substantially rectilinear in a given direction and separates two regions of different luminances, wherein the method comprises at least the functional steps of: carrying out,

1. A method for measuring the angular position of a contrasting edge of an object having a luminance transition zone which is substantially rectilinear in a given direction and separates two regions of different luminances, wherein the method comprises at least the functional steps of: carrying out, in a transverse direction different from the given direction, an amplitude modulation of the signals delivered by a first and a second optical sensor, by angular vibration of the optical axes of the first and second optical sensors, according to a given vibrational law, the vibration of the optical axes of the first and second optical sensors causing a vibration of the inter-receptor angle of the first and second optical sensors, the inter-receptor angle being delimited by the optical axes of the first and second optical sensors and containing the object with the luminance transition zone;calculating an output signal starting from the signals delivered by the first and the second optical sensors as a function of the angular position of the luminance transition zone, the output signal being independent of the vibrational law, and dependent on the angular position of the luminance transition zone relative to the mean optical axis of the device. 2. The method according to claim 1, wherein the output signal is the difference-to-sum ratio of the amplitudes of the temporally filtered signals delivered by the first and the second optical sensors. 3. The method according to claim 2, wherein the method comprises an additional step consisting of comparing the phases of the two temporally filtered signals, anddetermining whether the contrasting edge is a single contrasting edge or part of a thin bar, on the basis that two temporally filtered signals, measured for a single contrasting edge, are in phase and that two temporally filtered signals, measured for a thin bar, have opposite phases, a thin bar being the succession of two contrasting edges of opposite polarities. 4. The method according to claim 1, wherein the given direction and the transverse direction are orthogonal. 5. The method according, to claim 1, wherein the functional step of amplitude modulation consists in subjecting a lens having an optical center and being located between the stationary optical sensors and the luminance transition zone, or a group formed by the first and second optical sensors placed substantially in the image focal plane of the stationary lens to relative translational vibrations with respect to the luminance transition zone in said transverse direction. 6. The method according to claim 1, wherein in that the functional step of amplitude modulation consists in subjecting a group formed by the first optical sensor, the second optical sensor and the lens to relative rotation around an axis parallel to the given direction with respect to the luminance transition zone in said transverse direction. 7. The method according to claim 1, wherein characterized in that the functional step of amplitude modulation consists in maintaining a group consisting of the first and second optical sensors or a group consisting of the first and second optical sensors and a lens are stationary, while the luminance transition zone itself is vibrating. 8. The method according to claim 1, wherein in that the vibration of the optical axes of the first and second optical sensors in the transverse direction, is carried out by natural vibrations of a platform supporting the device. 9. The method according to claim 1, wherein the method comprises a step of demodulation of the signals delivered by the first and the second optical sensors before the step of calculating the output signal, the output signal being calculated starting from the demodulated signals. 10. A device for measuring the angular position of a contrasting edge of an object having a luminance transition zone which is substantially rectilinear in a given direction, the device comprising at least a first and a second optical sensor having an inter-receptor angle delimited by the optical axes of the first and second optical sensors, and the inter-receptor angle containing the object with the luminance transition zone, the device further comprising: a means for vibrational displacement of the optical axes of the first and second optical sensors in another direction transverse to the given direction, anda detection circuit comprising a means for calculating an output signal starting from the signals delivered by the first and the second optical sensors as a function of the angular position of the luminance transition zone, the output signal being independent of the vibrational law, and dependent on the angular position of the luminance transition zone. 11. The device according to claim 10, wherein comprises a lens having an optical center, the first and second optical sensors being placed substantially in the image focal plane of the lens and the average directions of observation of the first and second optical sensors corresponding substantially to two lines linking the centers of the first and second optical sensors and the optical center of the lens; and in that the means for vibrational displacement comprises, when said lens is stationary: a support element integral on the one hand, with a group formed by the first and second optical sensors and, on the other hand, with a stationary reference mechanical support;a means for applying, to said support element, a stress for controlling displacement to generate a translational displacement in the other direction of the group formed by the first and second optical sensors relative to said stationary reference mechanical support. 12. The device according to claim 11, wherein the device further comprises a means for orienting an assembly formed by the support element, the lens and the stationary reference mechanical support or an assembly formed by the support element, the group of the first and second optical sensors, and the stationary reference mechanical support, in order to orient the direction of the vibrational displacement of the lens or of the group in this other direction transverse to said given direction of the substantially rectilinear luminance transition zone. 13. The device according to claim 10, wherein the device comprises a lens having an optical center O, the first and second optical sensors being placed substantially in the image focal plane of the lens and the average directions of observation of the first and second optical sensors corresponding substantially to two lines linking the centers of the first and second optical sensors and the optical center of the lens; and in that the means for vibrational displacement in the other direction comprises, when a group formed by the first and second optical sensors is stationary: a support element integral, on the one hand, with said lens and, on the other hand, with a stationary reference mechanical support;a means for applying, to said support element, a stress for controlling displacement to generate a translational displacement of the lens relative to said stationary reference mechanical support. 14. The device according to claim 10, wherein the device comprises a lens having an optical center, the first and second optical sensors being placed substantially in the image focal plane of the lens and the average directions of observation of the first and second optical sensors corresponding substantially to two lines linking the centers of the first and second optical sensors and the optical center of the lens; and in that the means for vibrational displacement in the other direction comprises: a support element integral, on the one hand, with a group formed by the lens and the first and second optical sensors and, on the other hand, with a stationary reference mechanical support;a means for applying, to said support element, a stress for controlling displacement to generate a rotational displacement, around an axis parallel to the other direction, of said group relative to said stationary reference mechanical support. 15. The device according to claim 10, wherein the given direction and the other direction transverse to the given direction are orthogonal. 16. The device according to claim 10, characterized in that the detection circuit comprises a demodulator for demodulating the signals delivered by the first and the second optical sensors. 17. A set of devices comprising at least one lens, at least three optical sensors and a plurality of detection circuits, each pair of two consecutive optical sensors being placed close to the focal plane of one lens and connected to one of the plurality of detection circuits; in that one device comprises at least a first and a second optical sensor having an inter-receptor angle delimited by the optical axes of the first and second optical sensors, and the inter-receptor angle containing the object with the luminance transition zone, the device further comprising: a means for vibrational displacement of the optical axes of the first and second optical sensors in another direction transverse to the given direction, anda detection circuit comprising a means for calculating an output signal starting from the signals delivered by the first and the second optical sensors as a function of the angular position of the luminance transition zone, the output signal being independent of the vibrational law, and dependent on the angular position of the luminance transition zone; and in that each lens and each optical sensor are arranged substantially on a spherical, cylindrical or curved surface surrounding at least one local common centre, the at least one local common centre constituting the optical centre of an inter-receptor angle which is the sum over all inter-receptor angles of each of the devices taken together. 18. The set of devices according to claim 17, wherein the devices forming the set of devices are arranged in two directions substantially orthogonal. 19. A steering aid system for the visual fixation and fine tracking of a target, the target being an object comprising at least one contrasting edge having a luminance transition zone which is substantially rectilinear in a given direction and for controlling the angular speed of an aircraft, wherein the steering aid system comprises: a device for measuring the relative angular position of the contrasting edge of the target comprising at least a first and a second optical sensor having an inter-receptor angle delimited by the optical axes of the first and second optical sensors, and the inter-receptor angle containing the object with the luminance transition zone, the device further comprising: a means for vibrational displacement of the optical axes of the first and second optical sensors in another direction transverse to the given direction, anda detection circuit comprising a means for calculating an output signal starting from the signals delivered by the first and the second optical sensors as a function of the angular position of the luminance transition zone, the output signal being independent of the vibrational law, and dependent on the angular position of the luminance transition zone;a device for measuring a relative angular velocity of the contrasting edge of the target;a means to maintain the line of sight of the steering aid system constantly on the angular position of the contrasting edge; anda means to control an angular speed of the aircraft according to the angular position and angular velocity of the target. 20. A steering aid system for the visual fixation and fine tracking of a target, the target being an object comprising at least one contrasting edge having a luminance transition zone which is substantially rectilinear in a given direction and for controlling the angular speed of an aircraft, wherein the steering aid system comprises: a set of devices comprising at least one lens, at least three optical sensors and a plurality of detection circuits, each pair of two consecutive optical sensors being placed close to the focal plane of one lens and connected to one of the plurality of detection circuits; in that one device comprises at least a first and a second optical sensor having an inter-receptor angle delimited by the optical axes of the first and second optical sensors, and the inter-receptor angle containing the object with the luminance transition zone, the device further comprising: a means for vibrational displacement of the optical axes of the first and second optical sensors in another direction transverse to the given direction, anda detection circuit comprising a means for calculating an output signal starting from the signals delivered by the first and the second optical sensors as a function of the angular position of the luminance transition zone, the output signal being independent of the vibrational law, and dependent on the angular position of the luminance transition zone;and in that each lens and each optical sensor are arranged substantially on a spherical, cylindrical or curved surface surrounding at least one local common centre, the at least one local common centre constituting the optical centre of an inter-receptor angle which is the sum over all inter-receptor angles of each of the devices taken together;a device for measuring a relative angular velocity of the contrasting edge of the target;a means to maintain the line of sight of the steering aid system constantly on the angular position of the contrasting edge; anda means to control an angular speed of the aircraft according to the angular position and angular velocity of the target.