Mechanical system comprising a mixing unit, the mixing unit comprising: - a return means provided with a first hinge as well as a second hinge and a third hinge, the first hinge defining a first vertical axis of rotation and being hinged to a first mechanical output link, the second hinge defining a second vertical axis of rotation, the third hinge defining a third vertical axis of rotation, the first vertical axis of rotation as well as the second vertical axis of rotation being aligned in a first plane, the second axis of rotation and the third axis of rotation being aligned in a second plane; - an elongate mechanical member extending from a first end, which is hinged to the return means by the second hinge, to a second end, said elongate mechanical member including a fourth hinge that defines a fixed fourth vertical axis of rotation, the fourth hinge being suitable for being connected to a fixed support, said elongate mechanical member being only movable in rotation about said fourth axis of rotation, said elongate mechanical member including a link hinge which is hinged to a first mechanical link and which defines a vertical link axis of rotation, said first mechanical link being connected to a manual control member of said system; - a mechanical part only movable in rotation about said fourth axis of rotation by means of a pivot hinge, said mechanical part having an input hinge which is hinged to a second mechanical link and which defines a vertical input axis of rotation, said second mechanical link being connected to a manual control means of said system; - a connecting rod hinged at one end to the third hinge of the return means and at the other end to the mechanical part about a fifth vertical axis of rotation by a fifth hinge, the second axis of rotation as well as the third axis of rotation, the fourth axis of rotation and the fifth axis of rotation each and permanently forming a vertex of a deformable parallelogram in each plane that is orthogonal to these second, third, fourth, and fifth axes of rotation. - a return means provided with a first hinge as well as a second hinge and a third hinge, the first hinge defining a first vertical axis of rotation and being hinged to a first mechanical output link, the second hinge defining a second vertical axis of rotation, the third hinge defining a third vertical axis of rotation, the first vertical axis of rotation as well as the second vertical axis of rotation being aligned in a first plane, the second axis of rotation and the third axis of rotation being aligned in a second plane; - an elongate mechanical member extending from a first end, which is hinged to the return means by the second hinge, to a second end, said elongate mechanical member including a fourth hinge that defines a fixed fourth vertical axis of rotation, the fourth hinge being suitable for being connected to a fixed support, said elongate mechanical member being only movable in rotation about said fourth axis of rotation, said elongate mechanical member including a link hinge which is hinged to a first mechanical link and which defines a vertical link axis of rotation, said first mechanical link being connected to a manual control member of said system; - a mechanical part only movable in rotation about said fourth axis of rotation by means of a pivot hinge, said mechanical part having an input hinge which is hinged to a second mechanical link and which defines a vertical input axis of rotation, said second mechanical link being connected to a manual control means of said system; - a connecting rod hinged at one end to the third hinge of the return means and at the other end to the mechanical part about a fifth vertical axis of rotation by a fifth hinge, the second axis of rotation as well as the third axis of rotation, the fourth axis of rotation and the fifth axis of rotation each and permanently forming a vertex of a deformable parallelogram in each plane that is orthogonal to these second, third, fourth, and fifth axes of rotation.