Patent ID: 8511802

Claim:
A directivity detection device for detection of trajectories of drops issuing from a liquid jet, the drops being charged electrically, the device comprising: an electrostatic sensor comprising an electrically sensitive portion configured to detect an electrical charge, the electrically sensitive portion made of an electrically conductive material, the sensitive portion surrounded by an insulating portion made of electrically insulating material, the insulating portion being surrounded by an electric shielding portion made of electrically conductive material and connected to ground; the zones of the sensor delimiting at least one continuous flat surface, the sensitive zone of the sensor comprising at least four edges including an upstream edge and a downstream edge connected to one another by two lateral edges, the arrangement of the sensor being such that: the upstream and downstream edges are substantially perpendicular to the direction of the nominal trajectory of the drops and are each cut into two segments by a straight line H which is the geometric projection of the nominal trajectory on the flat surface; for each of the sides of the sensor delimited by the straight line H, the segment of the upstream edge and the segment of the downstream edge are of different lengths, the length of the longer segment being at least equal to the maximum permissible amplitude of the offset of trajectories to the side of the straight line H considered, relative to the nominal trajectory and the length of the shorter segment being at most equal to the maximum permissible amplitude of the offset of trajectories to the side of the straight line H considered, relative to the nominal trajectory; a signal-processing unit configured to process the electrical signal generated by the electrical charges of the drops through movement detected by the sensor, the signal processing unit being configured to: evaluate the level of an inlet peak Pe and the level of an outlet peak Ps of the representative signal of the electrical current derived from a charge in movement detected respectively at the level of the upstream edge and of the downstream edge of the sensor, calculate the value of a representative function of the difference between the levels of Pe and Ps, determine a first comparison of the value of the function with at least one first predetermined constant value or a range of predetermined values, and determine a second comparison of the level of the higher inlet peak Pe or outlet peak Ps relative to one another with at least one second predetermined constant value, the predetermined values being characteristic of the nominal trajectory of the drops, wherein the first comparison is indicative of the actual position of a trajectory of drops in a plane parallel to the flat surface of the sensor and the second comparison is indicative of the actual position of the same trajectory of drops in a plane perpendicular to the flat surface of the sensor.