BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the art of seismographic surveying, and more particularly, but not by way of limitation, to an improved hydraulic seismic vibrator of the type used to generate continuous seismic signals.
2. Description of the Prior Art
Many various seismic surveying systems have been developed which utilize a continuous wave seismic signal generated in the earth by a vibrator. Such vibrators generally comprise a base plate for engaging the surface of the earth, a reaction mass and a linear actuator, usually hydraulic, for reciprocating the reaction mass relative to the base plate at a desired frequency.
A particularly satisfactory hydraulic seismic vibrator or transducer which has heretofore been developed and used utilizes a fixed double-rod-end piston member and a reaction mass reciprocally disposed around the piston member forming a hydraulic cylinder whereby hydraulic fluid may be introduced to the cylinder to reciprocate the reaction mass. A conventional hydraulic fluid control system is utilized to alternately port hydraulic fluid under pressure to the two sides of the drive piston in the cylinder so that the reaction mass is moved from a central position in one direction, back to the central position, from the central position in the other direction, back to the central position, and so on. Depending upon the particular size and design of the vibrator, the weight of the reaction mass may vary from several hundred pounds to several thousand pounds. In order to offset the weight of the reaction mass, a differential pressure must be maintained across the piston which results in less net driving force available for moving the reaction mass in one direction than the other. This unbalanced force condition has been found to cause serious problems, among which is the generation of undesirable harmonic vibrations.
Heretofore, in order to offset or bias the weight of the reaction mass in a manner independent from the drive cylinder, auxiliary hydraulic cylinders connected to the outside of the reaction mass or machined into the reaction mass positioned away from the center line of the reaction mass have been used. It has been found that the use of such auxiliary biasing hydraulic cylinders often brings about excessive wear in the vibrator apparatus due to the unbalanced forces being applied to the reaction mass. Further, maintenance problems associated with the auxiliary hydraulic cylinders are numerous.
By the present invention an improved hydraulic vibrator is provided wherein the weight of the reaction mass is biased without producing unbalanced forces on the reaction mass and wherein the equipment and maintenance problems associated with auxiliary hydraulic biasing cylinders are obviated.
SUMMARY OF THE INVENTION
The present invention relates to a hydraulic vibrator having a fixed vertical piston member comprised of a pair of oppositely extending rods connected to a centrally disposed drive piston and a reaction mass reciprocally disposed around the drive piston forming a hydraulic cylinder so that when hydraulic fluid is introduced to the cylinder relative to the drive piston the reaction mass is reciprocated. By the present invention one of the rods of the piston member is provided with an upwardly facing annular shoulder to form a single acting piston. A downwardly facing annular shoulder is provided in the reaction mass and positioned to form a hydraulic biasing cylinder around the single acting piston whereby hydraulic fluid may be introduced to the biasing cylinder to bias the weight of the reaction mass. Port means for introducing hydraulic fluid to the biasing cylinder are provided connected to the biasing cylinder and to a source of constant pressure hydraulic fluid.
It is, therefore, a general object of the present invention to provide an improved hydraulic vibrator.
A further object of the present invention is the provision of an improved hydraulic vibrator of the type having a fixed vertical piston member and a reaction mass reciprocally disposed around the piston member wherein the weight of the reaction mass is biased by a hydraulic biasing cylinder which is positioned concentric with the axis of the reaction mass thereby producing no unbalanced forces on the reaction mass.
Another object of the present invention is the provision of an improved hydraulic vibrator wherein auxiliary hydraulic cylinder apparatus for biasing the weight of the reaction mass and maintenance problems associated therewith are obviated.
Other and further objects, features and advantages of the present invention will become apparent from the following detailed description thereof given for the purpose of disclosure when taken in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a side sectional view partially in diagrammatic form of the improved hydraulic vibrator of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawing, the improved hydraulic vibrator of the present invention is illustrated and generally designated by the numeral 10. The apparatus 10 basically comprises a frame 12 having a fixed double-rod-end piston member 14 attached thereto and a reaction mass 16 reciprocally mounted around the piston member 14.
The frame 12 may take a variety of forms, but generally includes a base plate 18 and an upper frame member 20 with an enclosure 22 connected therebetween.
The double-rod-end piston member 14 includes a lower rod 24, the end of which is connected to the base plate 18, an upper rod 26, the end of which is connected to the upper frame member 20, and a centrally disposed double acting drive piston 28. The drive piston 28 is slidably received within a cylinder 30 formed within the reaction mass 16. The piston 28 may be of any suitable conventional construction and may be provided with piston rings or the like to insure a sliding, fluid tight seal within the interior of the cylinder 30. The cylinder 30 may be formed within the reaction mass 16 by a plurality of sleeve inserts and sealing rings in a conventional manner.
Hydraulic fluid is introduced to the cylinder 30 alternately on opposite sides of the drive piston 28 by way of hydraulic fluid ports 32 and 34 disposed on opposite side of the piston 28. The ports 32 and 34 are formed in the rods 24 and 26, respectively, and are connected to a pair of passageways 36 and 38 also formed within the piston member 14. That is, the hydraulic fluid ports 32 are connected to one of the passageways 36 or 38 and the hydraulic fluid ports 34 are connected to the other of the passageways 36 and 38. The passageways 36 and 38 are connected by a pair of complementary passageways 40 and 42 disposed in the upper frame member 20 to a conventional hydraulic fluid servo or control valve 44 which is part of a conventional hydraulic drive and control system. The control valve 44 is activated by a suitable electric control system to cause hydraulic fluid under pressure to alternately pass to and from the cylinder 30 by way of the passageways 36 and 38 and hydraulic fluid ports 32 and 34 which in turn causes the reaction mass 16 to be reciprocated.
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