GB1120151A - Seismic radiator - Google Patents

Abstract

1,120,151. Reciprocating motors. McCOLLUM LABORATORIES Inc. 13 Sept., 1965, No. 39050/65. Heading H2A. [Also in Divisions F2 and H4] In an electromagnetically-driven seismic vibrator, an hydraulic fluid between a driving member and a radiating member coupled to the ground provides a proportional motion transmitting system in which the ratio of the displacement of the driving member to the displacement of the radiating member is greater than unity, thereby improving the mechanical impedance match between the driving member and the ground relative to the impedance match for a vibrator in which the driving member is directly coupled to the ground. In the embodiment shown, the permanent magnet stator of an electric motor comprises cylindrical cores 12, 13 clamped between outer pole plates 16, 17 and inner pole plates 14, 15 by a bolt 20, and is initially magnetized by coils 36, 37, the magnetic circuit being completed by sleeves 42, 43. The motor armature comprises a cylindrical coil 27 on a former 27a which is centred in annular chambers 67, 68 of the stator assembly by means of springs 30, 31 which also provide lead-in and lead-out connections for an input signal applied to the coil 27. Coil 27 can reciprocate between shoulders 25, 26 of sleeves 24, which limit movement of the coil during transportation of the vibrator. The stator assembly constitutes a reaction mass and is capable of limited reciprocal movement between end plates 3, 9 of a housing 1. Chambers 67, 68 and the chambers 65, 66 formed between the static assembly and end plates 9, 3 respectively, are filled with hydraulic fluid under pressure so that reciprocation of coil 27 which acts as a piston, results in an oppositely-phased reciprocation of the stator assembly and consequent vibration of a plate 5 which is coupled to end plate 3 and to the ground 6. To reduce the inductance of coil 27 and prevent demagnetization of the stator assembly, coils 36 and 37 are short-circuited and a cylindrical copper sleeve 21 is provided around cores 12 and 13. In an alternative embodiment (not shown), coils 36 and 37 are replaced by solid sleeves of copper or other heavy metal to provide similar shielding from eddy currents and demagnetization and to provide additional mass, the initial magnetization of the stator assembly being achieved by external electromagnets. To prevent variations of hydraulic pressure in housing 1 with changes of temperature of the fluid, a reservoir 70, in which compressed gas 72 is separated from hydraulic fluid 73 by a piston 71, is provided. It is stated that the seismic signal generated by the vibrator is a true analogue of the electrical signal applied to coil 27, which signal may be computer-controlled for subsequent computer processing of the seismic signals.