GB1387475A - Hydraulic or pneumatic actuators of the cylinder and piston type - Google Patents

Abstract

1387475 Fluid operated actuators SOC D'APPLICATIONS DES MACHINES MOTRICES 1 Feb 1972 [3 Feb 1971] 4727/72 Heading F1D An hydraulic or pneumatic actuator comprises an output rod 3 carrying pistons 5a, 5b slidable thereon, the pistons 5a, 5b being reciprocable in a main drive rod 1 having pistons 7a, 7b which are themselves reciprocable in a cylinder 2, and the rod 3 being normally pulled along with the main rod 1 but being displaceable relative to the rod I upon experiencing a predetermined external force. An annular chamber 6 between pistons 5a, 5b is connected via passage 10 in rod 1 to a further annular chamber 8 between pistons 7a, 7b which is in turn connected to a source of pressure via a passage 9 in cylinder 2. Passages 11a, 11b convey fluid into cylinder 2 for reciprocation of main rod 1. The pressure in chamber 6 urges pistons 5a, 5b apart against stop collars 3a, 3b on the rod 3 and against abutments la, 1b formed internally of rod 1. Thus it can be seen that rod 3 will normally follow all movements of rod 1. However, if an external force on rod 3 in either direction exceeds the force separating the pistons 5a, 5b due to the pressure in chamber 6, then a respective piston 5a, 5b will be moved by its associated collar 3a, 3b towards the other piston which will be held against its respective abutment 1a, 1b, Fig.3. The pressure in chamber 6 will remain constant and only when the external force F3 falls below the predetermined value will the original configuration, Fig.1, be restored. Applications of such an actuator are described Figs.4 to 6 (not shown) and an actuator in which the rod 3 is sensitive to an external force only in one direction is also referred to Fig.7 (not shown).