A kinematic mechanism is described, for changing the stroke of a cursor (15, 14") with reciprocating motion with respect to a fixed structure (1) and connected to a rotatable drive shaft (2, 1, 1") the mechanism comprises: eccentric means connected to the drive shaft (2, 1, 1") and adapted to transform the rotary motion of the drive shaft (2, 1, 1") into an alternate translating motion of an articulation point (12, 6, 4") of a kinematism guiding means for the articulation point (12, 6, 4") of a kinematism actuating means of the guiding means position detecting means of the guiding means and control means of the actuating means of the guiding means.
