Note: Descriptions are shown in the official language in which they were submitted.
This application is a divisional of S.N. 2~,4,737 ~iled 15 Auqust
l~377 and is direc-ted ~o a seisnuc energy source. The parent application
and other divisionals S.N. 3 ~ , S.N.-3~ , S.N. ~'~ S .N.
3'~ and s-N-~ ~ , all filed 6 July 1981 are also directed
to selsmic energy sources~
his invention relates to improvements in seismic energy sourc~s,
and in particular, to a broad band vibra-tory seismic energy source.
In the practice of expoloration seismology for the loca-tion of
subsurEace petroleum accumulations, it is necessary to provide a source
of energy for inducing propagating elastic waves in the area of the earth
to be explored. These elastic waves propagate down into the upper crust-
al material of the earth, are reflected from impedance discontinuities
located therein, and are subsequently detected by geophones or seismom-
eters located at the surface of the earth. The records produced by -the
geophones or seismometers contain much valuable information about the
crustal structure of the earth and may be used to ascertain the existence
of petroleum accumulations. It has become common in many cases to use,
as the source of propagating elastic waves, a hydraulically operated
vibratory source more simply referred to as a vibrator.
In a typical e~oodiment, a vibrator comprises a double ended
piston rigidly affixed to a coaxial piston rod. The piston is located in
reciprocating relationship in a cylinder formed within a heavy reaction
mass. Means are included for alternately introducing hydraulic fluid
under high pressure to opposite ends of the cylinder, thereby imparting a
reciprocating motion to the piston relative -to the reaction mass. The
piston rod extending from the reaction mass is rigidly coupled to a base-
plate which is maintained in intimate contact with the earth material.
Since the inertia of the reaction mass tends to resist displacement of
the reaction mass relative to the earth, the motion of the piston is
coupled through the piston rod and baseplate to impart vibratory seismic
energy in the e;arth~
Typically, the vibrators are transported by truck, and it is also
known to prevent decoupling of -the baseplate from the ground by applying a
-- 2 --
~3
1 portion of the truclc's we:ip,ht to the b~seplate during ope~tlon. The
weight of the truck is frequently appl:ied to the basep~ate through one or
more spring members, eacilllaving a large compliance, with the result that
a static bias force is imposed on the baseplate, while the dynamic forces
oE the baseplate are decoupled from the truck itself.
Conventional vibrators are capable of effective operation over a
relatively small range of low frequencies, typically 5 to 70 hert7. In the
past, these relatively low frequency vibrators have proven to be useful
seismic energy sources. As existing oil reserves become depleted, however,
1() it becomes necessary to search deeper and with increased resolution to
locate additional reserves. A broad band vibrator (BBV) capable of opera-
tion over a band of frequencies wider than those previously achievable with
kno~ln vibrators is useful in providing greater resolution and meaningful
interpretation at greater depth. Ln order to operate the vibrator so as to
provide significant output force levels at high frequencies, it is
necessary to minimize the weight of the baseplate and of other structural
elements rigidly affixed to the baseplate. In this way, the inertial force
which must be overcome solely to move the baseplate weight is minimi~.ed.
Further, it is necessary to provide sufficient force acting on the piston
to overcome the inertial force of the baseplate structure and still induce
significant energy in the earth.
The present invention provides various improvements in a BBV.
In one aspect the invention provides a seismic energy source comprising in
combination: a) a reaction mass having located therein R cylindrical
aperture, b) an actuator rod comprising a piston and piston rod, the piston
being located in the cylindrical aperture, and c) means for introducing a
fluid under high pressure into the cylindrical aperture to exert a force
on the piston, d~ the actuator rod having an internal bore with a diameter
that varies as a ~unction of position along the rod.
In a second aspect the invention provides a vibratory seismic
energy source hav-lng a double ended piston reciprocably mo~mted in the
cylinder of a reaction mass and a piston rod extendlng from opposite ends
-- 3 --
1 o~ tlle plston to project from the reactloil mass alld f-lrther comprising a
pair of relatively so~t bushings lining the bore of the reaction mass to
provide mechanical support for the portions of the piston rod located within
the reaction mass and for portions of the piston, the travel of the pi.ston
within the cylinder being limited so that each end of the piston remains
within one of the bushings at all times.
In another aspect the invention provides a vibratory seismic energy
source having a piston reciprocably mounted within the cylinder of a
reaction mass and at least one port in the wall of the cylinder for
admitting high pressure fluid to e~ert a force acting on the piston, the
piston being disposed in the cylinder such that when a piston over travel
condition occurs, the pi.ston substantially restricts the flow of fluid
through the at least one port thereby trapping a volume of fluid between the
face of the piston and the cylinder, whereby a braking force is generated.
In still another aspect the invention provides a seismic energy
source comprising in combination: a) force generat.ing means for providing
a force to be imparted to the earth and b) an aluminum baseplate for coupling
the force to the earth, thq baseplate defining a grid of internal cavities,
each cavity enclosed by four plane surfaces parallel to the general plane of
the baseplate and by two plane surfaces parallel to the general plane of the
baseplate intersecting the four perpendicular planes at the top and bottom
thereof respectively.
In another aspect the invention provides a vibratory seismic
energy source comprising: a) a reaction mass having a hydraulic cylinder
formed therein, b) an actuator rod including a piston reciprocably located
within the hydraulic cylinder, c) a baseplate, d) a frame member coupled to
an end of the actuator rod, and e) a plurality of stilt legs extending from
the frame member to the baseplate.
-3a-
A further aspect of the invention is a v:ibratory seismic energy
source transported by a vehicle and including a baseplate for coupling
seismic energy to the ground, at least one structural member adapted to
support at least a portion of the weight of the vehicle thereon, means for
coupling substantiall.y vertical forces from the structural member to the
baseplate, and stabilizing means for limiting translation of the structural
member relative to the baseplate. The stabilizing means may comprise a
L~
1 center link pivot~lly coupled to t~e b~seplate, a first stabilizing rod
rotatably coupled at one end to a point on the center link above the level
of its pivot and at the ot~er end to a flrst point of the structural member,
and a second stabilizing rod rotatably coupled at one end to a point on the
- center link below the level of i,s pivot and at the other end to a second
point of the structural member. Alternatively the center link can be
pivotally coupled to the structural member and the stabilizing rods to
the baseplate.
Finally, there is another aspect of the invention which is a
vibratory seismic energy source adapted to be transported on a vehicle,
including a vertically disposed piston and cylinder assembly, and a piston
rod extending downward from the piston and connected at its lower end to
a baseplate, a rigid plate interposed between the piston and cylinder
assemb]y and the ~aseplate, and adapted to permit motion of the piston rod
in relation to the rigid plate, elastic means supporting the rigid plate
from the baseplate and means for imposing at least a portion of the weight
of the vehicle on the rigid plate.
Preferred characteristics of the seismic energy source will be
discussed in the following description:
The ground contacting surface of the baseplate in the preferred
embodiment has àn area substantially less than that of conventional vibrators
in the 20,000 to 30,000 pound force range and has a square shape in contrast
with the typical rectangular shape of other vibrators. The baseplate area
of the BBV is less than that of existing vibrators, even though the peak
actuator force of the latter may be less than half that of the BBV.
The piston rod of the BBV is coaxial with the major axis of the
piston, and extends from both sides thereofO The lower segment of the
piston rod is rigidly coupled to the center of the baseplate, while the
upper segment of the piston rod is coupled through a structure consisting
of four stilts to the four corners of the baseplate. Thus, ~he baseplate
is supported both a~ its center and a~ each of its four corners. This
type of support, coupled with the unique two dimensional I-beam structure
-- 4 --
1 of the alumimlm baseplate~ provides a very light baseplate structure
capable of withstanding the high force levels generatred by the actuator
of the BBV.
Most known vibrators are carried by a vehicle havin~ a source of
motor power located near the front end of the vehicle and a drive line
extending therefrom to the rear end of the vehicle so as to engage a
differential assembly and ultimately to power the rear wheels of the
vehicle. Typically, the drive line extends through a portion of the
vibrator itself, and it is necessary to configure the vibrator such that
there is sufficient clearance for the drive line, whether the vibrator be
in its raised or lowered position. In the case of the BBV, the drive line
is eliminated and in the absence of a need to provide clearance for a drive
line, the vibrator dimensions, particularly its vertical extent, can be
substantially reduced. With the reduced dimensions, the stresses imposed
on certain structural members, particularly the stilt le~s, are less severe
and it becomes possible to make these members lighter.
.
- 4a -
~z~
;,~&,
1 In view of t~e reduced dimensions of the baseplate, previously
2 kno~l means for imposing the weight of the vehicle on the baseplate itself
3 become impractical. Accordingly, in an embodiment of the invention, a
4 unique one piece hold-down plate is provided to couple the weight of the
vehicle through air bags to the baseplate of the vibrator. Further in this
6 connection, and again in view of the reduced basepla~e dimensions, the use
7 of radius rods as a means for providing lateral stability between the hold-
8 down plate and the baseplate becomes difficult. In an embodlment of the
9 invention, a system of linkages sometimes referred to as a Watt's linkage
and adapted to the reduced baseplate dimensions~ provides excellent lateral
11 stability.
12 In the BBV, the reaction mass is a multiple piece structure
13 wherein the plurality of subassemblies are bolted together so as to provide
14 a unitary reaction mass. This economical means of fabrication results in
a reaction mass which provides the necessary high mass within the confines
16 of the stilt legs themselves. The stilt legs slant inward as they extend
17 upward from the baseplate, so as to provide effective resistance to hori-
18 zontal stress, as well as to the ver~ical stresses generated by the vibra-
19 tor itself.
The actuator piston and piston rod assembly of the BBV is pro-
21 vided with a hollow tapered bore, designed to result in constant stress as
22 a function of length along the rod and to minimize the mass of the piston
23 and rod assembly itself. Further, the piston and piston rod assembly
24 coopera~es with the cylinder of the reaction mass so as to provide an
internal braking mechanism for limiting piston over-travel.
26 Other objects and features of the inv~ntion will become obvious
27 from a consideration of the following detailed description when taken in
28 connection with the accompanying drawings wherein:
29 FIGURE 1 is a perspective view of a BBV.
FIGURE 2 is a cross sectional schematic view of portions of the
31 vibrator.
--5--
1 FIGUR~ 3 is a perspective vlew (partially cut away) of a base
2 plate.
3 FIGURE ~ illustrates the vibrator mounted in a truck.
4 FIGURE 5 is a perspective view illustrating stabilizing means for
a vibrator.
6 FIGUR~ h illustrates an alternative configuration for the sta-
7 bilizing means.
8 FIGURE 7 is a pareial sectional view of the cyllnder of a prior
9 art vibrator and of the ~BV.
FIGURE 8 is a sectional view of a vibrator actuator rod.
11 FIGURE 1 is a perspective view of a vibrator, portions of which
12 are shown in cross section in FIGURB 2. Referring to FIGURES 1 and 2, a
13 baseplate 17 is driven by a hydraulic drive mechanlsm comprising a driving
14 piston 103 reciprocably mounted within a cylindrlcal bore 101, and a pistonrod 104 carrying piston lG3 and extending from both the top and bottom of
16 the cylinder housing lOla. The lower end of piston rod 104 is rigidly
17 affixed to the center of the baseplate and the top is rigidly affixed to
18 the center of frame member 106. Stilt legs 108a, 108b, 108c, and 108d (the19 latter not visible in FIGURE 1) extend in slanting relationship from the
baseplate to ~oin the corners of frame mPmber 106 to the corners of the
21 baseplate.
22 It is an ob;ect in constructing the BBV to reduce the mass moving23 with the ground while the vibrator ls generating a seismic wave. This
24 "baseplate weight" consists of the actual baseplate which couples the
actuator force to the ground and all components, structures, and members
26 rigidly attached to the baseplate. A minimum baseplate weight ls of
27 pa~amount importance in high frequency operation. With a fixed peak
28 actuator force available, the only force which may be coupled into the
29 ground is the actuator force minus the ~orce used to move the baseplate
weight. The less force re~uired to move the baseplate, the more there i5
31 available to be imparted to the ground.
--6--
1 The equation for the force magnitude required to move a mass at a
2 specific frequency, assuming sinusoidal motion, is:
3 F=(W/g)A(2 ~f) sin (2 ~ft~
4 where:
F= force,
6 W~ "baseplate weight",
7 A= mass displatement (1/2 of peak-to-peak),
8 g~ acceleration of gravi~y,
9 f~ driving frequency, and
t= time.
11 With a displacement of A, the force req~ired increases with
12 Erequency as a function of the frequency squared. This illustrates the
13 need for a mlnimum baseplate weight W for high frequency operation.
14 To achieve the ob~ective of minimum baseplate weight while re-
taining structural rigidity, the ground coupling plate (baseplate) is
16 constructed from two aluminum sections, 17a and 17b, the internal surfaces
17 of which have a honeycomb appearance. One surface of each of the plate
18 sections may be milled out as illustrated in FIGURE 3. In a preferred
19 embodiment, the baseplate may be square, having dimensions of four feet on
each side. Each of the baseplate sections may be approximately 3-1/2"
21 thick. As shown in FIGURE 3, the internal sides of both sections of the
22 baseplate are m~lled out in a 16 x 16 grid, of 3" each. Individual sectlons
23 may be milled out to a depth of 2.85 inches, with .25 lnches left between
24 each milled out section. It should be emphasized that the dimensions can
vary, depending on the force and rigidity requirements of a particular
26 vibratory structure.
27 Certain portions of the baseplate sections, such as those desig-
28 nated by numeral 29, are left unmilled in order to provide locations for
29 bolting the tw~ section~ eogether. In the top portion of the baseplate,
holes, such AS ~hose designated by numeral 31 are drilled, and bolts, such
1 as bolt 32, are inserted through these holes to secure the cwo sections of
2 the baseplate together. Corresponding holes, such as those designated by
3 numeral 33, are drilled into the bottom section of the baseplate. Screw
~ ~hreaded receptacle means are inserted in the bottom section of the base-
plate to recei~e the bolts inserted through the holes in the top section.
In general, the holes utilized for securing the two sections of the base-
7 plate together are posltioned so that the connecting bolts also affix
8 additional vibrator structure to the baseplate.
9 It is known in the seismic vibrator art to fabricate the gene-
rally rectangular baseplate of a plurality of parallel steel I-beams. '~he
11 longitudinal a~es of the I-beams are located parallel to the major axis of
12 the rectangle and adjacent I-beams are oriented so the edges of their upper
13 and lower flanges are abutting (the webs of the I-beams lie in vertical
14 planes). The I-beam flanges are welded together so as to provide a unitary
structure which may be further reinforced by top and bottom reinforcing
16 plates. It will be appreciated that this type of structurc provides great
17 resistance to stress exerted along the maior axis of the rectangle. While
18 the resistance to stress may be expected to be less along the minor axis of
19 the rectangle, the use of steel I-beams resulted in a b~seplate with suffi-
cient stress tolerance for the force levels employed in prior art vibra-
21 tors.
22 In the case of the BBV, the use of a steel baseplate structure
23 would impose a severe weight penalty on the vibrating mechanism. Alterna-
24 tively, an aluminum baseplate structure comprised of a pluralit~ of one-
dimensional I-beams might not have sufficient stress resistance for the
26 forces generated by the BBV. It will be appreciated that the ~wo-piece
27 aluminum baseplate structure of the present invention, when bolted together
28 as set forth above, comprises a un-lque two dimensional I~beam structure.
29 As a result of this unique structure, the baseplate may be maintained
within acceptable weight limitations and yet be capable of withstanding the
--8--
28~
1 large forces generated by the BBV. In this descript-lon and in the acco~n-
2 panying claims the term "two-dimensiona:L I-beam structure" is considered to
3 include structure such as that i:Llustrated in FIGURE 3 as well as similar
4 structures such as one having a plurality of I-beams radiaLing from the
baseplate center. Further, in the structure of FIGURE 3, it is not neces-
6 sary that the I-beam webs be coplanar from cell to cell of the structure.
7 The center of the baseplate is rigidly connected to the lower end
8 of piston rod 104. Piston rod 104 may have an annular Elanged portion at
9 the lower end with a plurality of holes therein. The same bolts that function
to secure the cen~er portions of the baseplate sections together affix the
11 piston rod to the baseplate.
12 As stated earlier, the top of piston rod 104 is connected to the
13 center of frame member 106. Connected at each corner of this frame member
14 is an inclined stilt leg which :is ~ixedly connected to a corner of the
lS baseplate. When vibrations are lnduced by controlled hydraulic fluid flow
16 into and from cylinder 101, motion generated in the piston is transmitted
17 to the center and to each of the ~our corners o the baseplate. This
18 configura~ion is a very rigid vibratory structure which produces a uniform
19 movement of the entire baseplate closely corresponding to tlle motion of the
piston.
21 The stilt legs 108 are sub~ected to a complex form of loading.
22 l'he loading consists of vertical and horizontal forces. The vertical load-
23 ing i5 due to the simple vibratory operational mode of the piston 103. The
24 piston rod 104 is of adequate strength to withstand the vertical loading~
The horizontal loading is due to ground rocking and ground
26 resonances. Because the rigidity of the stilt legs 108, when loaded hori-
27 zontally, is many times greater than the rigidity of piston rod 104 as a
28 cantllever, only the stilt legs provide significant resistance to hori-
29 zontal loading. In doing so, the horizontal loading appears primarily as
tension or compression in the stilt legs 108. The stilt legs provide
~2~
`~...
1 greater strength when loaded ln either compression or tenslon than when
2 sub~ected to bendlng forces. ~e use of inclined stilt legs i.8 superior
3 because of the efficient structural use of its members. r~le efficiency of
4 the inclined stilt legs permits the stilt leg dimenslons to be reduced
below ~hose whicll would be necessary if previously kno~m stilt leg con-
6 figuration (i.e., vertical legs) were employed. ~t will be seen, there-
7 fore, that the unique stilt leg configuration further contributes to mini-
S mization of the baseplate weight. The baseplate weight is reduced even
9 further by the elimination of the lower cross member, commonly used in
~revious vibrators.
11 For the purpose of imparting vibratory movement to the piston
12 103, there is provided a manifold and servo valve member 19. The servo
13 valve follows the electrical control signal fed to it through conducting
14 leads l9a. Hydraulic actuating power for the servo valve is supplied
through line ~3 from an external hydraulic power source, including pump 42
16 and reservoir 48 (see FIGU~E 2~. The servo valve controls the flow of
17 hydraulic fluid into and from cylinder 101 through port means 64 and 66
18 within the walls of cylinder housing lOla above and below piston 103 to
l9 generate piston motion corresponding to the electrical input control sig-
nal. Hydraulic supply mechanisms are well known in the art and need not be
21 discussed in greater detail here. One such mechanism is disclosed in U. S.
22 Patent No. 3,929,206.
23 The hydraulic vibrator generates a force against the ground by
24 pushing against a reaction mass comprising the mass or cylinder housing
lOla, plus addltional mass affixed to the cylinder housing. l`his addition-
26 al mass includes manifold and servo valve member 19, which in the preferred
27 embodiment is mounted on the orward portion of the vibrator. The addi~
28 tional mass further includes rear balance weight lOlb and side weights lOlc
29 and lOld. Thus, it will be seen that the reaction mass is a "multi-piece
bolt together" mass consisting of a center section lOla which houses the
--10--
~z~
1 actuator, two side welghts 101~ and lOld, a rear balance weight lOlb, and
2 the manlfold and servo valve member 19. ~le mass pieces are shaped so that
3 the stilt legs pass through but do not touch the mass shapes.
4 The weight of the hydraulic cylinder housing and mass attached
thereto is decoupled from the baseplate mass by air spring 37 which is
6 attached to the top of frame member 106. Two vertically extending me~nbers,
7 130a and 130b, connect the top of the reaction mass to a frame member 134
8 affixed to the top of the air spring 37. Air spring 37 is an isolation
g spring and also sets the average position of the hydraulic piston 103 in
the center of the cylinder to ensure more linear operation of the hydraulic
11 vibrator. Air spring 37 is inflated to a desired pressure through a con-
12 ventional fill valve shown as valve 140. Two arcuate sections 136a and 136b
13 (the latter not shown) are affixed to the bottom of frame member 134 on
14 opposite sides thereof, and a layer of elastic material 138 is attached to
ïS the lower edges thereof. This elastic layer serves as a buffer when the
16 up-stroke of the hydraulic piston is too large. A comparable structure
17 (not shown) functions as a buffer when the down-stroke is too large.
18 As is common practice in the art, the body of the vibrator is
19 ïocated between the frame members of the truck. In the usual design of
hydraulic vibrators, the baseplate extends outwardly from the vibrator, and
~1 vertical guide rods and hydraulic lift cyllnders extend fro~ the truck
22 frame to a "footpiece" above outwardly extending portions of the baseplate.
23 The weight of the vibrator transport truck is applied to the baseplate
24 through the "footpiece" and spring isolation means to assist in holding the
baseplate on the grolmd. In the present vibrator, in addition to milling
26 out portions of the baseplate, the dimensions of the baseplate have also
27 been reduced in order to reduce the moving mass. Because of the reduced
28 si~e, the baseplate does not extend from beneath the vibratory body suffi-
29 ciently to permit applying the truck weight to the baseplate in the con-
ventional manner. A unique one-piece hold-down plate 50 permits the use of
--11--
l the small baseplate. The welght of the truck ls transferred to the hold-
2 do~l plate hydraulic lift cylinders 5 and 7 (see FLGURES 1 and 4). The
3 hol~-down plate e~tends beneath the reaction ma.ss and rests upon four air
~ bags 33a, 33b, 33c~ and 33d (the latter two not shown in FIGU~E 1), which
are affixed bet~een the hold-down plate and the baseplate. The air bags
6 may preferably be spaced at regular intervals around the baseplate to
7 couple the weight of the truck to ~he baseplate evenly. The vibrator
8 piston rod extends through the center portion of the hold-down plate which
9 has a cut out section for that purpose. In addition to permitting the use
of a small baseplate, the hold-down plate also provides a means for dis-
11 tributing the air springs so as to couple the weight of the transport truck
12 to the baseplatP in a more uniform manner about the surface of the base-
13 plate. In the preferred embodiment, air bags 33a, 33b, 33c, and 33d are
l4 pneumatically isolated. It is possible, however, for the air bags to be
pneumatically coupled without departing from the spirit and scope of the
16 invention.
17 llydraulic lift cylinders 5 and 7 (see FIGURES 1 and 4) control
18 the vertical position of the vibrator relative to the truck. ~he cylinder
19 housings of lift cylinders 5 and 7 are affixed to the truck frame and the
piston rods thereof are affixed to the hold-down plate. When hydraulic
21 fluld is pu~ped into the upper portion of the lift cylinders 5 and 7, the
22 pistons are forced down relative to the cylinders and the vibrator is
23 lowered to the ground. ~fter the baseplate is lowered to the earth's
2~ surEace, if additional hydraulic fluid is pumped into the upper portions of
lift cylinders 5 and 7, the truck will be lifted off the ground and its
26 weight will bear on the hold-down plate. The air springs which inter-
27 connect the hold-down plate with the baseplate transmit the weight of the
28 truck to the baseplate. The truck is lowered back to the ~round and the
29 baseplate lifted off the ground by pumping hydraulic fluid into the lower
-12-
r
l portions of the lift cylinders 5 and 7. As ~he baseplate is lifted off the
2 ground, it i5 suspended from the hold-down plate by means of a plurality of
3 chalns ~. Guide rods 6a and 6b (see FIGURES l and 4) slide through the
4 cylindrical bores of guide frames 9a and 9b (ga not shown) which are
rigidly affixed to opposite sides of the transport truck. These guide rods
6 are normally interconnected so that they move up and down in unison.
7 Techniques for performing this function are well known in the art and need
8 not be discussed here, one such technique being shown in the aformen~ioned
9 U. S. Patent No. 3,929,206~
Because air springs 33a, 33b, 33c, and 33d have little resistance
11 to lateral stress, a linkage mechanism is used to maintain the baseplate in
12 vertical alignment with the vibrator and to apply the weight of the truck
13 substantially to the center of the baseplate. This horizontal stabiliza-
14 tion is required to not interfere with or detract from, to any appreciable
extent, the desired vertical motion of the baseplate. Further, the horl-
16 zontal stabilization mechanism should impose no appreciable horizontal
17 motions to the truck. It i5 known ln the art to use for thls purpose, a
18 multiplicity of radius rods, one end of each radius rod being pivotally
19 attached to the baseplate, and the other end being pivotally attached to a
part of the lift mechanism of the truck.
21 This radlus rod type of stabillzation system provides good hori-
22 zontal control between the baseplate and the hold-down plate of the vehicle
23 li~t system. ~te radius rod system, however, does impose undesirable
24 horizonta~ motion to the hold-down plate as the baseplate moves vertically.
The undesirable horizontal motions become more severe as the radius rod
26 length is decreased, as it would have to be if this type of stabilization
27 system were used on the BBV. It is common practice in the design of vi-
28 brators to use pairs of radius rods mounted so that they are in opposition.
29 The tendency for horizontal displacement as the vibrator moves vertically
is taken up by rubber bushings in the eye ends of the radius rods. Deflec
31 tion of the rubber bushings, howe~er, takes energy from the vibrating
32 baseplate.
-13-
9l~
1 With reference to I~'IGURES 1 and 5, a linkage mechanism designated
2 by numeral 150 is used to maintain the baseplate of the BBV in vertical
3 alignment with the truck. The linkage mechanism is comprised of equal
4 lengch rods 152a and 152b and rotating center link 154. An end of each
equal length rod is connected to a nounting assembly 156 rigidly affi~ed to
6 the corners of the baseplate. The other end of each equal length rod is
7 connected to center link 154. Center link 154 is connected in the center
8 thereof in a rotating manner to plate 158 which extends downwardly from the
9 hold-down plate in substantially vertical alignment with the edge of the
hold-down plate. Center link 154 rotates freely about this center con-
11 nection and the two equal length rods rotate freely about a connection to
12 opposing ends of center link 154. The ends of the equal length rods con~
13 nected to mounting assembly 156 are also rotationally free. One of these
14 linkage mechanisms 154 is affixed to each side of the vibrator baseplate.
This mechanism permits the baseplate to move up and down relative to the
16 hold-down plate while maintaining vertical alignment. When the baseplate
17 moves down in relation to the hold-down plate the center link 154 will
18 rotate in a counterclockwise direction. ~1hen the baseplate moves up rela-
19 tive to the hold-down plate, center link 154 rotates in ~ clockwise direc-
tion. In a preferred embodiment, the ends of rods 152a and 152b may be
21 connected by a ball ~oint to the mounting assembly connec~ed at the corners22 of the baseplate, to permit an additional degree of freedom. This linkage
23 mechanism permits the baseplate to tilt relative to the hold-down plate.
24 Therefore, if the vibrator is on ground which is not in parallel alignment
with the plane of the truck, the baseplate can tilt so as to rest evenly on
26 the ground.
27 In the preferred embodiment, the center link and its pivot are
28 attached to the hold-down plate, while the extremities of rods 152a and
29 152b are pivotally attached to supports on the baseplate. Alternatively,
the center link and pivot may be attached to the baseplate, while the
-14-
~2~9~
..,~ .
1 extremities of the rods can be pivotally attached to supports on the hold-
2 down plate. The arrangement of the preferred embodiment, however, has a
3 distinct advantage when the vibrator is operating on sloping ground. With
4 reference to FIGURE 6a, which illustrates the arrangement of the preferred
embodiment, the baseplate is driven by the vibrator along a line perpen-
6 dicular to the baseplate and ground. The baseplate is a:Lso guided along
7 this same line by the constraint imposed by the linkage. FIGURE 6b illus-
8 trates the arrangement of the alternative embodiment wherein the baseplate
9 motion is again along a line perpendicular to the baseplate and the ground,
while the linkage tends to constrain the motion to a vertical line. Thus,
11 the stabilizing linkage in this case will impose horizontal forces between
12 the baseplate and the hold-down plate.
13 In the preferred embodiment, stabilizing rods 152a and 152b have
14 equal length and center link 154 is symmetrically disposed about its pivot
point. It is also within the contemplation of the invention to use sta-
16 bilizing rods of unequal length and a non-symmetLical center link.
17 In the preEerred embodiment, the length of each of stabilizing
18 rods 152a and 152b is 19 inches, while the distance between the points at
19 which the stabilizing rods are coupled to center link 154 is 5.625 inches.
As an example of the effectiveness of the stabilizing means, if the base-
21 plate moves vertically with respect to the hold-down plate by a distance of
22 2 inches, there will be a relative horizontal displacement between the
23 baseplate and hold-down plate of 0.00021 inches. If a radius rod suspen-
24 sion were used in this case (with a rod length of 38 inches), for a ver-
tical displacement of 2 inches there would result a horizontal displacement
26 of 0.0527 inches. Thus, the stabilizing linkage employed in the BBV re-
27 duces the horizontal displacement by a factor of 250.
28 From the foregoing, it will be seen that the unique stabilizing
29 system provides several important advantages. Vertical translation of the
baseplate results in negligible horizontal motion imparted to the support-
31 ing truck by the stabilizat~on system. Further, the space required for the
~z~
l stabilization system is reduced. Finally, the energy absorbed by the
2 stabilization system is reduced, thereby increasing the net seismic energy
3 into the ground.
4 FIGURE 7a is a sectional view of the cylinder area of the re-
action mass from a prior art vi~rator. FIGURE 7b is a sectional view of
6 the corresponding portion of an embodiment of the present invention. All
7 vibrators are provided with an over-travel limit system which serves to
; 8 prevent the piston from traveling beyond its nominal stroke to the point
9 where the piston impacts an end of the cylinder. ~ost vibrator actuators
have springs or externally mounted hydraulic shock ahsorbers as part of the
11 over-travel limit system. That type of over-travel limit system has
12 several features which render it undesirable for use in the present vibra-
13 tor. The first problem relates to the effective oil volume in the cylinder
lll of the actuator. A frequency is reached at which the volume of the oil
within the cylinder acting as a spring resonates in con~unction with the
16 load mass. This oil column resonance places an upper limit on the range of
17 frequencies over which the vibrator can operate. The frequency of oil
18 column resonance varies inversely with the square root of effective volume
19 oE oil within the cylinder. Accordingly, it will be seen that in the BBV
it is essential to minimize this effective oil volume.
21 As the piston moves from the center of the cylinder to the limit
22 of its stroke, it sweeps a volumè of oil from the piston equal to the
23 product of the piston area and its length of stroke. If the piston travel,
24 however, e~ceeds its nominal stroke, it will sweep an additional volume of
oil equal to the product of the piston area and the length of over travel.
26 Thus, this additional oil volume, for which no benefit is received, is
27 proportional to the distance that the piston over travels before the over-
28 travel limit system stops it. The amount of over travel with prior art
29 externally mounted limit systems is large and results in an effective
cylinder oil volume that is undesirable for the present invention.
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1 Additlonally, the use of external shock absorbers reduces the re-
2 liabi]ity of an over-travel limit system. For example, if the plunger
3 fails to reset due to a broken return spring or if nvt enough time has
4 e]apsed for a normal resetting before the over travel condition repeats, no
S shock absorber action will occur. In an embodiment of the present inven-
6 tion, there is provided an internal over-travel limit system which is reset
7 if the actuator ls in the working stroke. Whiie an internal over-travel
8 limit system i6 known in the prior art, the internal limit system oE the
9 present inventioll has several features which render it more advantageous
for use in a high frequency vibrator.
11 The essential features of the prior art internal limit system are
12 illustrated in FIGURE 7a. There is shown in sectional view a portion of a
13 reaction mass 200 including the cylinder region of the reaction mass. ~n
~-4 axial hollowed out portion of circular cross section extends through the
reaction mass. This hollowed out portion is lined over part of its length
16 by bron~.e bushings 202 and 204 which serve to support in sliding relation-
17 ship, the piston rod 206 of a double ended piston. The cylinder area of
18 reaction mass 200 is lined by a sleeve 208 of a metal such as cast iron.
19 Piston 210, including a plurality of piston rings, is reciprocably located
within the confines of the cylinder. Clearance is provided between the
21 walls of the piston and the inner surface of sleeve 208 so that only the
22 piston rings are in contact with sleeve 208. Ports 212 and 214 communicate
23 with the manifold ~not shown~ so as to admit oil under hlgh pressure al-
24 ternately to oppos~te sldes of the piston. Port 212 opens into an annular
passage 216 which extends around the outer circumference of bushing 202.
26 Passage 216 in turn communicates with a plurality of holes 218 located in
27 and about the circumference of bushing 202. ~lus, it will be seen that
28 high pressure oil from the manifold is admit~ed through port 212, passage
29 216 and holes 218 into a portion of the cylinder formed by the inner surface
~2~
~h~
1 of bushing 202 and a narrowed portion of piston rod 206. The oil so ad-
2 mit~ed may fiow into the main body of the cylinder so as to generate a
3 orce ac~ing against one side of the piston. In a silllilar ll~anner, oil from
~ the manifold flows through port 214, channel 220 and holes 222 to the
opposite end of the cylinder.
6 The internal braking action provided by the illustrated structure
7 may be appreciated from the following brief operational discussion. Let it
~3 be assumed that o:il is admitted under high pressure through port 214 to the
9 right side of the cylinder. This causes the piston 210 and piston rod 206
to move to the left and oil from the left side of the cylinder is exhausted
11 through port 212 to a reservoir of low pressure oil. This continues until
12 shoulder 224 of the piston rod reaches and begins to enter bushing 202. ~t
13 this point in time, a volume of oil is trapped in region 226 of the cylin-
14 der. This trapped volume of oil imparts a braking action to the piston and15 prevents it from impacting the end of bushing 202. The piston braking is
16 accomplished by the trapped volume which escapes slowly through the small
17 clearance provided between the portion of piston rod 206 which is not
18 narrowed and the inner surface of bushing 202~ Because of the high pressure
19 occurring in region 226 during braking action, it is necessary to provide
an 0-ring 228 for preventing the escape o~ oil between bushing 202 and
21 reaction mass 200. A corresponding 0-ring 230 is provided at the other end
22 of the cylinder. In the structure illustrated, it will be noted that the
23 piston and piston rod are unsupported over the entire region between
24 shoulder 232 and shoulder 234. In the prior art vibrator illustrated, this
is a length of approximately 16.5 inches.
26 The internal hydraulic braking action provided by an embodiment
27 of the present invention may be illustrated with the aid of FIGURE 7b which
28 shows a sectional view of a portion of the reaction mass lOla. Reaction
29 mass lOla is provided with an axial bore extending through its entire
length.
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l2~
1 The bore is llned at its ends by bushings 252 and 254 which
2 provide bearing surfaces for the piston rod 104 of a double ended piston
3 103. In the preferred embodiment bushings 252 and 254 are made of bron~e.
4 Other materials, however~ may be used Eor the bushings. One such suitable
material is a polymide manufactured under the trade mark VESPEL by Dupont.
6 Bushings 252 and 254 also serve to support piston 103 in the areas indi-
7 cated by reference designators 260 and 262. In the region of the piston
8 rings~ the surface of the bore is lined by a sleeve 264 of a metal such as
9 cast iron.
Ports 64 and 66 communicate with the manifold (not shown) to
11 serve as input and exhaust ports for oil entering and leaving the cylinder.
12 Yort 64 opens into an annular passage 270 which extends around the outer
13 circumference of bushing 252. Passage 270 in turn communicates with a
14 plurality of slots 272 formed in bushing 252 whereby oil is admitted to and
exhausted from one side of the cylinder. In a similar manner, port 66
16 cooperates with annular passage 274 and slots 276 to provlde a path for the
17 oil to the opposite end oE the cylinder.
18 During operation of the vibrator, as high pressure oil is ad-
19 mitted through port 66 so as to exert a force against the piston driving it
to the left, oil is forced out through port 64 to a low pressure reservoir.
21 During normal operation, prior to the time w'nen piston 103 passes the
22 plurality of ports 272, the flow of oil will be reversed so as to admit
23 high pressure oil to port 6~ and allo~ oil to leave the cylinder through
24 port 66 to the low pressure reservoir. Under abnormal conditions, however,
the piston may excPed its designated stroke and travel sufficiently far to
26 the left to close off slots 272, thereby trapping a volume of oil in the
27 end of the cylinder. This trapped oil is bled back to the slots through
23 the radial clearance between piston 103 and bushing 252. The concentricity
--19--
1 and radial clearances are selected to obtain a desired shock absorber
2 action. The equation used to predic~ the shock absorber response is:
RC tl ~ 3~ )
4 where
FD = Retarding force,
6 l = Oil viscosity,
7 L ~ Length of engagement
8 L' = Relative velocity between the rod and
g rod bushing,
ro = Small rod diameter,
11 R = Rod bushing cavity radius,
12 r = Piston radius (plunger),
13 C = R - r = radial clearance,
14 e = eccentriclty, piston relative to cavity, and
E = C
16 The internal shock absorber illustra~ed in FICURE 7b is superior
17 to the prior art arrangement of FIGURE 7a in several respects~ First,
18 piston 103 is always engaged in bushings 252 ancl 254 at regions 260 and 262
19 respectively. Accordingly, there is no mechanical "plunger" insertion into
the bushing. This enhances the reliability of the mechanism.
21 Secondly, since mechanical support for the piston is provided by
22 bushings 252 and 254 in regions 260 and 262, respectively, the longest
23 unsupported length of the actuator rod structure is that portion of the
24 piston that is enclosed within liner 264. In the preferred embodiment,
this unsupported portion of the piston extends only over a length of 9.2
26 inches. By reducing the unsupported length of the piston, the stresses
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z~
1 exerted on the actuator rod are relatively reduced. As will be d:Lscussed
2 below in connection with FIGURE 8, this permits the piston rod assembly to
3 be hollow, thereby further reducing the weight of the baseplate and asso-
4 ciated elements.
When the over travel condition occurs, in the preferred embodi-
6 ment the oil is trapped between the piston 103, the piston rod 104, and
7 either of bushings 252 and 254. As a result, it is not necessary to pro-
8 vide 0-rings corresponding to 0-rings 228 and 230 ln FIGURE 7a. These 0-
9 rings are required in the prior art structure since~ there, the braking oil
volume is trapped ahead of bushings 202 and 204. Elimination of the 0-ring
11 reduces the actuator cost. Further, it will be noted that piston rod 104
12 does not require the additional machining operations required to produce
13 the reduced diameter section of piston rod 206 in the prior art structure.
14 Finally, in the preferred embodiment, there is no oil volume corresponding
to that volume of oil located between the reduced diameter section of
16 piston rod 20~ and bushings 202 and 204 in the prior art structure. As
17 mentioned previously, this reduced oil volume is advantageous in high
18 frequency operation of the vibrator.
19 FIGURE 8 is a sectional view showing the configuration of the
actuator rod 280. The rod is hollow so as to reduce the baseplate weight
21 of the vibrator. The tapered bore of the rod is specifically designed such
22 that the stresses resulting from forces applied transverse to actuator rod
23 280 are approximately constant as a function of distance along the rod. As
24 a result, no portion of the rod is "over-designed" (and correspondingly
over-weight) relative to another portion of the rod.
26 The diameter of the sleeve in which the piston 103 runs, in the
27 preferred embodiment, is nine inches, while the diameter of the piston rod
28 is seven inches. As a result the effective piston area at either end of
-21-
I the piston is 2i.13 square inches. Ilydraulic fluid is supplied to the BBV
' at a pressure of 3000 psi. ~ccordingly, it will be seen that the peak
3 force acting on the piston of the BBV is 75,390 pounds, far in excess of
4 that used in other vibrators.
There has been disclosed a new seismic vibrator, suitable for
6 operation over a broad band of frequencies. I~hereas the preferred embodi-
7 ment of the invention has been disclosed, there may be suggested to those
8 skilled in the art certain minor modifications which do not depart from the
9 spirit and scope of the invention as set forth in the appended claims.
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