1. An active vibration damping system for a rolling stand, in particular for
rolling strips, comprising two or more working rolls (1, 1’) with respective chocks
(20), the damping system comprising:
a plurality of hydraulic actuators (2’, 2’’, 2’’’, 2iv) having respective movable pistons (3’, 3’’, 3’’’, 3iv) acting on said chocks (20), and respective chambers (6’, 6’’, 6’’’, 6iv), a hydraulic circuit for feeding said plurality of hydraulic actuators (2’, 2’’, 2’’’, 2iv), one or more injectors (8’, 8’’, 8’’’, 8iv) within said hydraulic circuit,
characterized in that said one or more injectors (8’, 8’’, 8’’’, 8iv) are directly arranged within or in the proximity of the structure of the respective chambers (6’, 6’’, 6’’’, 6iv) of the hydraulic actuators (2’, 2’’, 2’’’, 2iv) to actuate an active damping of the vibrations of the working rolls (1, 1’), said injectors being adapted to inject pressurized oil into a respective chamber (6’, 6’’, 6’’’, 6iv) of the hydraulic actuators (2’, 2’’, 2’’’, 2iv) under the control of an electronic control unit (5).
2. The active damping system as claimed in claim 1, wherein said hydraulic
circuit comprises an actuating line (11) adapted to draw oil from a first hydraulic
station to feed said hydraulic actuators (2’, 2’’, 2’’’, 2iv), and a high-pressurized
branch (12), having an oil pressure greater than the operating pressure along the
actuating line (11), adapted to draw oil from a second hydraulic station,
and wherein said injectors (8’, 8’’, 8’’’, 8iv) are adapted to put in communication the respective chambers (6’, 6’’, 6’’’, 6iv) of the hydraulic actuators (2’, 2’’, 2’’’, 2iv) with said high-pressurized branch (12).
3. The active damping system as claimed in claim 1 or 2, wherein the one or more injectors (8’, 8’’, 8’’’, 8iv) are of the piezoelectric type.
4. The active damping system as claimed in claim 1, wherein the injection orifice (65, 75, 85) of the injectors is in direct communication with a respective chamber (6’, 6’’, 6’’’, 6iv).

5. The active damping system as claimed in claim 1, wherein the injection orifice (65, 75, 85) of the injectors is in direct communication with a first side of a connecting sleeve (50), placed in the proximity of a respective bending chamber and connected thereto by means of a conduit extension (51).
6. The active damping system as claimed in claim 5, wherein the conduit extension (51) connects a second side of the connecting sleeve (50) to the bending chamber, while the actuating line (11) is connected to said conduit extension (51) by means of a third side of the connecting sleeve (50).