Acoustics – Geophysical or subsurface exploration – Seismic wave generation
Patent
1984-08-13
1985-03-26
Moskowitz, Nelson
Acoustics
Geophysical or subsurface exploration
Seismic wave generation
181121, 367189, 73665, G01V 1135, G01V 104, F01B 1500
Patent
active
045067589
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to transducers for inducing vibrational signals in an elastic medium, and more particularly, but not by way of limitation, it relates to an improved construction for a relatively high frequency transducer for generating seismic waves in the earth.
2. Description of the Prior Art
The prior art includes hydraulic vibrators having drive cylinders and biasing cylinders as is illustrated by U.S. Pat. No. 3,745,885 issued to Fair et al. on July 17, 1973. The Fair et al. apparatus is constructed for operation in normal frequency ranges of approximately 2-80 cycles per second. Yet another patent of particular interest is U.S. Pat. No. 4,106,586 in the name of Stafford. This teaching provides a vibrator assembly wherein the cylinder end sleeves are adjustable between two extreme positions to either shorten or lengthen the hydraulic cylinder. The present invention provides a form of apparatus generally similar to that of Fair et al. but suitable for a much higher operating frequency range up to and exceeding 250 cycles per second.
SUMMARY OF THE INVENTION
This invention provides a hydraulic transducer cylinder and mass assembly for a seismic source that is capable of generating high force output over a wide frequency of seismic signals, the hydraulic fluid compressibility in the hydraulic system which drives the transducer is a limiting factor. Therefore, to maintain a high natural frequency of the fluid compressibility and the effective mass, the ratio of hydraulic cylinder area to trapped fluid volume must be optimized to as high a value as possible within the scope of practical design and operating conditions.
The present invention meets these requirements by using a relatively large area short stroke cylinder, and by using relatively short passages between the drive cylinder and the servo-valve. To obtain these relatively short passages, the drive cylinder is located close to the servo-valve, and the hydraulic biasing cylinder is located below the drive cylinder, i.e., rather than above the drive cylinder as was shown in U.S. Pat. No. 3,745,885, and the high pressure fluid is ported from the servo-valve through the piston rod to the drive cylinders. In addition, the servo-valve is mounted with the main valve spool perpendicular to the piston rod axis for valve stability; and the valve is mounted at or near the center of the piston rod end to decrease passage length and to more nearly equalize the passage length to each side of the cylinder.
Finally, the cylinder assembly of the present invention provides a drive cylinder the length of which may be varied so as to allow the transducer to operate over different frequency ranges by changing the allowable stroke of the drive piston within the drive cylinder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partly sectional side elevation of the seismic transducer of the present invention, showing some of the components in schematic form.
FIG. 2 is an elevational view of an alternative embodiment of the piston rod assembly of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings and particularly to FIG. 1, the hydraulic vibrator apparatus or seismic transducer of the present invention is shown and generally designated by the numeral 10.
The hydraulic vibrator 10 includes a frame assembly generally designated by the numeral 12. The frame assembly 12 includes a plate section 18, a frusto-conical section 20, and a cylindrical section 22. Frame assembly 12 as made up by its component sections constitutes a rigid housing that provides a secure interconnection between the upper piston rod end 30, to be described, and the baseplate 14 which, in turn, is rigidly affixed to the lower piston rod end 34.
Thus, a vertical double rod-end piston member 24 includes a drive piston 26, an upper rod 28 extending from drive piston 26, an upper end 30 attached to plate section 18, and a lower rod 32 extending from piston 26 and having a lo
REFERENCES:
patent: 3143181 (1964-08-01), Boys et al.
patent: 3745885 (1973-07-01), Fair et al.
patent: 4106586 (1978-08-01), Stafford
patent: 4253538 (1981-03-01), Weber et al.
Miller William J.
Moskowitz Nelson
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