Improvements relating to Linear Hydraulic Motors

1,155,001. Hydraulic reciprocating motors. FERRANTI Ltd. July 11, 1967 [April 12, 1966], No. 15838/66. Heading F1A. In a linear hydraulic motor comprising a translator 13 movable relative to a stator 11 by the sequential pressurization of cylinders A, B... in the translator, so that hardened steel balls A1, A2... in the cylinder engage a cyclic edge profile 12 on the stator to cause the relative movement, the sequential pressurization of the cylinders is controlled by spool valves P1, P2, &c. operated in sequence in response to signals emitted each time the translator moves through a distance equal to a predetermined fraction of a wavelength of the cyclic profile. The spool valves P1, P2 receive hydraulic fluid Fs through channels II or 12, dependent on the position of a changeover valve 21, the channel not pressurized being connected to exhaust Fe. Each spool valve (there may be more than two) controls the supply and exhaust to two groups of cylinders, one group being pressurized while the other is exhausted. Several methods of producing the signals for causing the spools to changeover are described. In the first method, the signals are produced by an optical fringe-counting method, in which a photocell 26 on the translator traverses a grating 25 of alternate light and dark bands, whereby electrical signals S1 S2 are emitted at each predetermined fraction of a wavelength to actuate the spools via relays R1, R2. Alternatively the electrical signals are emitted by switches actuated by cams engaging the profile. In the second method the spools are actuated hydraulically, Fig. 5 (not shown), by fluid directed thereto by pilot valves operated by the profile.