Motion transmission group for capping heads for screw caps and capping machine equipped with such a motion transmission group

Motion transmission group for capping heads for screw caps, wherein said capping heads are provided with means for axially engaging the caps, wherein said group is intended to be operatively associated with a capping machine and comprises a main structure extending along a longitudinal axis between a coupling end for a capping head and a drive end, axially opposite to the coupling end, at which the group is configured to receive in input from a capping machine translation movements along said axis and rotation movements around said axis to be transmitted in use to said capping head, wherein said group comprises a device for applying in use a predefined axial load to the axial engagement means of the caps, which a capping head associated in use to said coupling end is provided with, wherein said device in turn comprises at least one axially pre-loaded compression spring so as to generate in use said predefined axial load, wherein said device comprises a support structure for said at least one compression spring, said support structure being suitable to keep said compression spring arranged coaxially to said axis in a predefined pre-loading condition by means of a first and a second axial positioning portion, associated with a main body of said support structure in axially different, positions, wherein said support structure is shaped in such a way that said at least one compression spring is engageable directly or indirectly from the outside of said support structure to allow in use the operational coupling with the axial engagement means or the caps, which a capping head associated in use to said coupling end is provided with, and wherein said device is separable from the main structure of said transmission group as a single body, with said at least one spring kept associated to said main body of said support structure in a pre-loaded condition by said two axial positioning portions, to allow the replacement of said device with a structurally similar device, but suitable to generate a different axial load in use.