Variable stiffness actuator

It is provided a variable stiffness actuator (1) adapted to move a movable component (102) and comprising: two electric motors (4) of the rotary type, at least one output shaft (3) adapted to be set in rotation by said two electric motors (4) around a rotation axis (3a); an elastic transmission system adapted to enable motion transfer from said motors (4) to said output shaft (3) and to vary the stiffness of said output shaft (3); a control unit (9) adapted to adjust at least the stiffness of said output shaft (3) through said elastic transmission system; and a holding structure (2) defining an outer surface and an inner volume (2a) adapted to hold at least said two electric motors (4), elastic transmission system, output shaft (3) and control unit (9); finally, the holding structure (2) has: a driving output (3b) placed at the outer surface, which is controlled by the output shaft (3) and is adapted to set the movable component (102) in rotation about the rotation axis (3a), at least one stiff coupling element (5) adapted to enable a stiff connection of the holding structure (2), and a support output (2e) that is opposite to the driving output (3b) and substantially coaxial with the rotation axis (3a) and is adapted to partly house the movable component (102) stabilising the rotation of said movable component (102).