Absolute-control numerical hydraulic actuating device

A numerical hydraulic actuating device for absolute-control of an output position for a piston, comprising a distributor having a moving part connected to the piston and comprising at least one land portion which moves along a main row of distributor orifices formed in a stationary part of the distributor so as to cover them in succession, the device also comprising a numerically-actuated selector means connected to the various orifices in order to selectively establish hydraulic connections required to produce a certain number of discrete coarse locking positions of the piston, the piston which is of the differential kind having on one side a chamber of a small cross-section permanently connected to a high-pressure source which supplies fluid to the device, and on the other side forming an active chamber of a larger cross-section which is supplied with fluid at a variable pressure from the distributor, the land portion of the movable part of the distributor being bounded by the ends of two aligned longitudinal grooves which are communicated with the high-pressure source and with a low-pressure source respectively, and the distributor orifices which are formed along a corresponding generatrix of the stationary part being spaced axially from one another in a number equal to that of the wanted locking positions and being each connectable through the selector means to the active chamber whereas the remaining orifices are disconnected, the improvement wherein, in order to increase the number of locking positions by providing intermediate positions, the land portion of the movable part of the distributor is given an axial length substantially greater than that of the various orifices in the main row, that, in addition to the main row of distributor orifices, the stationary part of the distributor is formed with a number of auxiliary rows made up of collecting orifices which can be selectively connected by the selector means to the active chamber and alternate with fluid orifices which in turn can be selectively connected to the high-pressure and low-pressure sources, and that the auxiliary rows of orifices aligned along separate generatrices of the stationary part of the distributor cooperate with an equal number of longitudinal grooves formed along corresponding generatrices of the movable part to define fine locking positions of the piston, starting from the coarse positions of the piston obtained by means of the main row of distributor orifices.