Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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13168~1
METHOD AND APPARATVS POR AUTOMAT~CALLY
CONTROLI,ING PRFSSI~E IN PLUq~UATED SYSTEMS
Field of the Invention
This invention relates to fluid-actuated systems and, more
5 particularly, to methods and appnratus for automntically controlling the pressure
in such systems.
Background of the Invention
Fluidic pressure is employed in a variety o~ applications requiring
the application of pressure to a workpiece or load. For example, fluidic pres~ure
10 can be used to actuate clamps that hold a workpiece securely in place on ~ piece
of industrial e~uipment. Similarly, clamps used to grasp a load for lifting can be
actuated by fluidic pressure. Specific applica~ions include the use of flui~
actuated robot arms in manufacturing plants and hostile work environments, as
well as fluid-actuated forklifts used when the weight or bulk Or a load makes it15 inconvenient for human handling. The fluidic pressure developed cnn be above or
below (vncuum) that of the atmosphere nnd the type of fluid employ~d cnn be
either hydraulic or pneumatic.
A particular application of interest involves the use of a single set
of fluid-actuated clamps to lift loads that can be light and soft or relatively
20 he~vy and hard. One of the problems encountered in using a fluid-nctuated
system in this application is the need to control the pressure applied by thc
clamps to the different loads. For a relatively soft, light load, n light pressure
must be Rpplied to lift the load without damage. A relatively hard, heavy load,
however, requires the application of additionnl clamp pressure to produce a grasp
25 that is firm enough to lift the load. Because of the relatively rigid nature of the
load, the additionnl pressure applied does not damage the load. This level of
pressure would, however, tend to crush the relatively soft, light load.
~ To produce the level of clamp pressure required to lift the load
without damagej~ some adjustment in fluidic pressure must be made for the
30 various loads lifted. The use of a single, pressure limit switch controlling the
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supply of fluld to the clamps would clearly be inadequate. With the switch
adjusted to provide the pressure needed to lift a hard, heavy load, relatively soft,
light loads would be crushed. On the other hand, with the switch adjusted to
prevent the establishment of pressure sufficient to damage light loads, relatively
5 heavy loads could not be lifted.
One device that seems to address the foregoing problem is that
disclosed in U.S. Patent No. 3,168,2D3 (GaUistel). The GaUistel apparatus
provides an operator with a tactile sense of the pressure exerted by a hydrQulicactuator upon a load. In response to the tactile sense experienced, the operatorlO tightens or loosens the manual pressure applied to a handgrip that controls the
actuator. In this manner, the pressure applied to the load is correspondingly
increased or decreased. While the Gallistel apparatus appears capable of
grasping and lifting dissimilar loads without damage, it suffers the distinct
disadvantage of requiring feedback from a human operator. In many spplica-
l5 tions, an QUtOmatic system, free from humnn involvement, i9 desired. It is thisproblem to which the present invention is addressed.
Sum m ary of the Invention
In accordance with this invention, an apparatus is provided for
automatically controlling the force applied by a clamp to a load. The clamp is
20 typically closably actuated by the introduction of fluid into a clamp actuator
cylinder controlled by the apparatus.
In accordance with a particular aspect of this invention, an initial
predetermined ~luid pressure is developed in the actuator cylinder by a portion of
the apparatus including a reservoir containing a supply of fluid, an initial conduit
25 connecting the reservoir and actuator cylinder, a pump for transferring fluidfrom the reservoir to the actuator cylinder, and a normally open valve
interrupting the conduit between the pump and actuator cylinder. Pursuant to
this arrangement, ~luid is transferred from the reservoir to the actuator cylinder
until the initial predetermined pressure in the actuator cylinder is reached,
30 closing the normnlly open valve. I~pon establishment of the initial pre-
determined pressure in the actuator cylinder, a first predetermined volume of
fluid is then discharged to the actuator cylinder. This is accomplished by a first
cylinder connected in parQUel with the initial conduit and containing a first free-
~lonting piston. When the normally open valve closes, the first piston is
35 displaced in the cylinder, discharging the first volume of fluid to the actuator
cylinder.
In accordance with another aspect of this invention, a second
cylinder ~nd normally closed valve are placed in paraUel with the first cylinder.
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The normally closed valve opens only when the d~scharge by the first cylinder
increQses the pressure in the ~ctuator cylinder by a predetermine~ amount. At
that time, Q second ~ree-floa~ing piston located In the second cylinder disch~rges
~ second predetermined volume of fluid from the second cylinder to the actuator
5 cylinder. In this manner, additional pressure is applied ~o the load by the
actuating cylinder only when the load is relatively rigid, thereby protecting soft,
light loads from damage.
In accordance with a further aspect o~ this invention, nt lea.st one
additional controllable fluid discharge cylinder is employed similar to the second
10 cylinder. The output of the ndditional cylinder is control]ed by a normally closed
valve that opens only when the discharge of the second volume oî fluid to the
actuator cylinder increases the pressure in the actuator cylinder by nn additionnl
predetermined amount. When this occurs, an additional predetermined volume of
fluid, within the additional cylinder, is discharged to the actuating cylinder. By
15 selecting the desired number of additional cylinders employed, and their r~
spective additional volumes of fluid and additional operating pressures,
continuum of pressure adjustments can be provided, as desired.
In accordance with another aspect of this invention, Q method is
provided for automatically controlling the force applied by a clamp to a load.
20 The method includes the steps of applying a first predetermined level of force to
the clamp, which transfers the force to the load in a predetermined manner, and
applying a second incremental level of force to the clamp when the first
predetermined level of force is reached. The method may further include the
step of applying an additional incremental level of force to the clamp when the
25 load exhibits a predetermined resistance to the application of the second
incremental level of force to the clamp.
In accordance with a particular aspect of this invention, the above
method includes the steps of producing an initial predetermined pressure in the
actuator cylinder and discharging a first predetermined volume of fluid to the
30 actuator cylinder when that initial predetermined pressure is reached.
The method may also lnclude the steps of discharging a second
predetermined volume of fluid to the actuator cylinder when the discharge of thefirst volume of fluid increases the pressure in the actuator cylinder by a
predetermined amount and discharging at least one additional predetermined
35 volume of fluid to the actuator cylinder when the pressure in the actuator
cylinder exceeds an additional predetermined pressure.
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Accor~ing to a broad aspect of the invention there is
provided an apparatus for automatically controlling the pressure
applied by a clamp to a load, said clamp being closably actuated
by the introduction of a fluid into a clamp actuator cylinder
operatively coupled to said clamp, said apparatus comprising:
initial pressure establishment means, connected to said actuator
cylinder, for producing an initial predetermined pressure in said
actuator cylinder; and f-irst controllable fluid discharge means,
connected to said actuator cylinder, for discharging a first
predetermined volume of said fluid to said actuator cylinder when
said initial predetermined pressure in said actuator cylinder is
reached.
According to another broad aspect of the invention there
is provided an apparatus for automatically controlling the
pressure applied by a clamp to a load, said clamp being closably
actuated by the introduction of a fluid into a clamp actuator
cylinder operatively coupled to said clamp, said apparatus com-
prising: pressure establishment means for transferring fluid to
said actuator cylinder; an initial conduit connecting said
pressure establishment means to said actuator cylinder; valve
means for interrupting the flow of fluid in said initial conduit
between said pressure establishment means and said actuator
cylinder, said valve m.eans interrupting the flow of fluid when
an initial pressure in. said. actuator cylinder is reached; first
controllable fluid discharge means, connected to said actuator
cylinder, for discharging a first predeterm.ined volume of said
fluid to said actuator cylin.der when said initial predetermined
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pressure in said actuator cylinder is reached; and second control-
lable fluid discharge means, connected to said actuator cylinder,
for discharging a second predetermined volume of said fluid to
said actuator cylinder when the discharge of said first volume
of fluid to said actuator cylinder increases the pressure in said
actuator cylinder by a predetermined amount.
According to another broad aspect of the invention there
is provided an apparatus, for controlling the pressure developed
by the introduction of a fluid into an actuator cylinder, said
fluid stored initially in a reservoir and withdrawn from said
reservoir by a pump, said apparatus comprising: first control-
lable fluid discharge means, connected to said actuator cylinder,
for discharging a first predetermined volume of said fluid to
said actuator cylinder; and second controllable fluid discharge
means, connected to said actuator cylinder, for discharging a
second predetermined volume of said fluid to said actuator
cylinder when the discharge of said first volume of fluid to said
actuator cylinder increases the pressure in said actuator cylinder
by a predetermined amount.
According to another broad aspect of the invention
there is provided an apparatus for controlling the pressure
developed by the introduction of a fluid into an actuator cylinder
from a fluid source, said apparatus comprising: first control-
lable fluid discharge means for discharging a first predetermined
volume of said fluid to said actuator cylinder, said first fluid
discharge means comprising a ~irst discharge cylinder having
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a first free~floating piston disposed between a source-end of
said first cylinder and an ac-tuator end, said source being for
introducing fluid into said source-end and forcing said first
piston toward said actuator end of said first cylinder when said
pressure in said actuator cylinder exceeds a first predetermined
pressure, discharging said first volume of fluid to said actuator
cylinder; and second controllable fluid discharge means, connected
to said actuator cylinder, for discharging a second predetermined
volume of said fluid to said actuator cylinder when the discharge
of said first vclume of fluid to said actuator cylinder increases
the pressure in said actuator cylinder by a predetermined amount.
According to another broad aspect of the invention
there is provided a method for controlling the pressure developed
by the introduction of a fluid into an actuator cylinder, said
method comprising the steps of: discharging a first, predeter-
mined volume of fluid to said actuator cylinder; and discharging
a second, predetermined volume of fluid to said actuator cylinder
when said step of discharging said first volume of fluid to said
actuator cylinder increases said pressure in said actuator
cylinder by a predetermined amount.
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Brief Descri~tion of the Drawings
The invention will preselltly be described in gre~ter detail, by way
of example, with reference to the accompanying drawings wherein:
FIGURE l is a pictorial view of a forklift employing the method
5 and apparatus of the present invention to lift loads of vE3rious weights flnd
rigidity without damage; and
PIGURE ~ is a schematic diagram of a fluid-actuRted system,
constructed in accordance with the present invention, at an initial operating
point.
I0 Detailed Description of the Preferred Embodiment
.
As shown in FIGURE 1, one application for the method and
apparatus of the present invention is the control of clamping force developed bya forklift 10. ~ pressure control system 1~, connected to forklift clamps 14,
controls the pressure exerted by clamps 14 upon loQd 16. The pressure is
15 automatically controlled in a manner that allows both hard, heavy loads and soft,
light loads to be lifted without damage. Pressure control system 12 is fluid
actuated and may be either hydraulic or pneumatic, although in the currently
preferred embodiment a hydraulic system is employed. While both clamps 14, as
described below, are fluid actuated, it will be appreciated that only one of the
20 clamps need be controlled in this manner, with the position of the other being
fixed.
The method and apparatus of the present invention will now be
considered in greater detail with respect to FIGURE 2. System 12 is actuated by
a hydraulic fluid selected on the basis of a number of factors. These factors
25 include, for example, the desired viscosity, viscosity index, pour point, com-
pressibility, stability, lubricating ability, volatility, aeration resistance, and
materials compatibility of the fluid.
A reservoir 18 is included in system 12 and serves a number of
functions. Its primary use is to provide a convenient source of fluid for pump 2û,
30 which supplies the remainder of system 12 with pressurized hydraulic fluid.
Reservoir 18 includes enough fluid to allow the system to operat~ properly during
cylinder extension or in the event of Q small leak. The construction of reservoir
18, and volume of fluid contained therein, a1so allows turbulent fluid returningfrom system 12 to settle and de-aerate. This function of reservoir 18 provides a35 higher quality hydraulic fluid for reintroduction into system 12 by pump 20. In
applications where the operation of system 12 rQises the temperQtUre of the
hydraulic fluid, reservoir 18 can also be used to exchange heat between the fluid
and the environment of the reservoir 18, cooling the hydr~ulic ~luid. Reservoir
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18 can be integral with, or separate from, the remainder of system 12 and is
typically located so that gravity alds the return of fluid through system 12 to
reservoir 18.
Pump 20 is typically of the positive-displacement type used for
5 flui~power applications. Its function is to transfer fluid from reservoir 18 into,
and through, system 12. The pressure rating, volumetric flow output, efficiency,fluid compatibility, and size and weight of pump 20 are selected for com-
patibility with the remainder of system 12.
A three-position, manually Qctuated control valve 22 controls the
10 output of pump 20115 well as the inlet to reservoir 18. Valve 22 is typically of
the spool, poppet, or slide mechanism type. In a first position, A (see
FIGURE 2), valve 22 allows fluid to pass from pump 20 through the portion of
system 12 that CQUSeS clamps 14 to close. In a second position, B, vRlve 22
allows pump 20 to feed the portion of system 12 responsible for opening
15 ciamps 14. In Q third position, C, system 12 is hydraulically isolated from both
reservoir 18 and pump 20.
A conduit 24 conducts fluid from pump 20 and control valve 22 to
clamp actuator cylinders 26. Conduit a~ can be made of pipe, tubing, or hose
selected in consideration of a number of factors. These factors include, for
20 example, the maximum system pressure expected, conduit flexibility require-
ments, the need for system disassembly, the fluid type involved, and the
expected system operating temperature. MQny of these same factors also effect
the size and construction details of the p~rticular conduit type selected.
Although not shown in FIGURE 2, conduit 24 is attached to the vnrious system
25 components by fittings constructed to provide connections of the requisite
integrity.
~ ctuator cylinders 26 are typically cylinders of the double-acting,
force~return type. The body 28 of each actuator cylinder 26, in cooperation
with a piston 30, defines a pressure chamber open to conduit 24 and into which
30 hydraulic fluid is introduced by the action of pump 20. A rod 32 is connected to
piston 30 and ext~nds through one end of body 28 where it is connected to clamp
14. ~s will be apparent, introduction of fluid into the actuator cylinder chamber
exerts a force against piston 30, causing clamps 14 to apply force to load 16.
The mounting details, si%e, senls, nnd pressure rating of actuator cylinders 26 are
35 selected in accordance with the reguirements of the particulur application.
~ normally open control valve 34 and check valve 36 interrupt
conduit 24 between control valve 2a and actuator cylinders 26. Normally open
v~lve 34 includes a body 38 defining a chamber in which a spooled piston 40
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resldes. The posltlon of piston 40 wlthln valve 34 is biased by a
colled c~lindrlcal spring ~2. In this posltlon, the reduced
dlameter mldsection of plston 40 is allgned wlth condult 24 inlet
and outlet ports provlded on valve 34, allowlng fluld
communlcatlon therethrough.
Check valve 36 lncludes a body 44 havlng a restrlcted
lnner dlameter at a polnt ad?acent the lnlet port oE condult 24.
A ball 46 seats against the reduced dlameter portlon of body 44
downstream ~toward actuator cyllnders 26) of the inlet port. Thls
conflguratlon allows fluld pumped through condult 24 to pass
through chec~ val~e 36 to actuator cyllnders 26. Pressurlzed
fluld ln the actuator cyllnders 26 ls, however, prevented from
returnlng through condult 24 and check valve 36 because the
pressure of the fluid seats ball 46 flrmly agalnst the reduced
dlameter portlon of check valve body 44, blocklng the flow
therethrough.
The portlon of system lZ descrlbed so far, except actua-
tor cyllnders 26 and clamps 14, ls used to establlsh an inltial
predetermlned pressure ln actuator cyllnders 26. Whlle a detalled
descrlptlon of the operatlon of thls portlon of system 12 ls given
below, the remainlng elements of system 12 wlll flrst be descrlb-
ed. These elements lnclude a flrst source of controlled fluld
discharge 50, a second source of controlled fluld dlscharge 52, an
addltlonal source of controlled fluld dlscharge 54, and a rellef
valve 56.
As shown ln FIGURE 2, the flrst source of controlled ?
fluld dlscharge 50 includes a first discharge cylinder 58 located
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along a condult 60 that ls connected ln parallel with the portlon
of condult ~4 contalning normally open control valve 34. A free-
floatlng plston 62 ls dlsposed wlthln flrst cyllnder 58 and
separates pump-end and clamp-end chambers 64 and 66, respectlvely,
defined within the body 68 of flrst cylinder 58.
The second source of controlled fluld dlscharge 52
lncludes a second dlscharye cyllnder 70 whose output ls controlled
by a normally closed control valve 72. Cyllnder 70 and valve 72
lnterrupt a condult 74 connected ln parallel wlth condult 60. The
body 76 of second cylinder 70 deflnes pump-end and clamp-end
chambers 78 and 80 separated by a free-floatlng plston 82.
Normally closed control valve 72 lncludes a body 84,
whlch houses a spooled plston 86. Plston 86 ls normally blased by
a colled, cyllndrlcal sprlng 88 such that plston 86 blocks the
flow of fluld from second cyllnder 70 through valve 72 and condult
74.
As shown ln FIGURE 2, system 12 may lnclude one or more
addltlonal sources of controlled fluid dlscharge 54. Each
addltional dlscharge source 54 lncludes an addltlonal discharge
cyllnder 90 whose output ls controlled
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by a norm~lly closed control valve 92. These components interrupt Q conduit 94
placed in par~lel with conduit 74. Additional discharge cylinder 90 includes ~
body 96, which, together with a free-floating piston 98, defines pum~end and
clamp-end chambers 100 and 102, respectively.
Normally closed control valve 92 includes Q body 104 having a
spooled piston 108 disposed therein. A coiled, cylindrical spring 108 bi~ses
piston 106 to block the flow of fluid from additional cylinder 90 through valve ga
and conduit 94.
Finally, relief valve 56 is a normally closed valve constructed
10 similarly to valves 72 and 92. ~ spooled piston 110 is provided in valve body112. Piston 110 is biased by Q coiled, cylindrical spring 114 to restrict fluid flow
through a conduit 116 connecting the elamp ends of conduits 60, 74, and 94, to
the reservoir side of eontrol valve 22.
The operation of the above embodiment of system 12 will now be
15 described. ~s illustrated in FIGVRR 2, system 12 is at rest nnd no pressure is
exerted upon the load or workpiece. When the manually aetuated eontrol valve
22 is switched to its closed pOsitioll, however, the pump ao supplies fluid fromreservoir 18 and sends it through conduit 24, normally open valve 34, and cheek
valve 36 to retraction chambers 118 in actuator cylinders a6. ~9 fluid is
20 introduced into the retraction chambers 118, rods 32 retract into cylinders 26,
drawing elamps 19 against the load or workpieee.
Once elamps 14 contaet the load, the physieal presence of the load
interferes with the further retraetion of rods 32 into eylinders 26. Thus, as pump
20 eontinues to supply fluid from reservoir 18 to conduit Z4, the pressure in
25 eonduit 24 and retraetion chambers 118 increases. This inerease in pressure is
also experienced by the fluid in compression ehamber 120 of norm01ly open
valve 34. Compression chamber 1a0 is located on the side of piston 40 opposite
spring 42 and is connected to the aetuator cylinder side of eonduit 24 by a branch
of that conduit. Thus, as the pressure in conduit 24, retraction chambers 118 and
30 compression chamber 120 increases, the force applied to the side of piston 40opposite spring 42 increases. This process continues until the pressure in
chamber 120 is sufficient to overcome the force of spring 42 and move piston 40
from its normally open position to a position blocking conduit 24. By properly
configuring spring 42, the flow of fluid through conduit 2~ directly from pump 20
35 can be halted when a desired, predetermined pressure in retraction chambers 118
of actuator cylinders 26 is reached. Because the force applied to the load or
workpieee is proportional to the pressure in retraetion ehamber 118, it is clear
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that vnlve 34, constructed in the foregoing manner, closes when a predetermined
amount o~ force is applied by clamps 14 to the load.
Prior to the actual closure of normally open control valve 34, the
first source of controlled fluid discharge 50 becomes operative. The initial
position of fre~floating piston 62 is such that clam~end ehamber 66 constitutes
a substantial portion of the interior of cylinder 58. Both the pump-end and
clamp-end chambers 64 and ~6 are filled with fluid. As the piston 40 in normallyopen valve 34 moves toward its closed position, the action of pump 20 begins to
cause additional fluid to flow through conduit 60 and into the pump-end chamber
6~ of the cylinder 58. The continued action of pump 20 causes the pressure in
the pump-end chamber 64 to exceed that in the clamp-end chamber 66, driving
piston 62 through cylinder 58 and forcing the hydraulic fluid from clam~end
chamber 66. Because the initial volume of fluid in clam~end chamber 66 can be
controlled, a first predetermined volume of fluid is introduced into conduit 24
and retraction chambers 118 ~fter valve 34 closes.
In the event that the load or workpiece is relatively soft, the
introduction of this first predetermined volum~ of hydraulic fluid into conduit 24
and chambers 118 of actuqtor eylinders 26 causes rods 8a to retract farther intocylinders 26. The load or workpiece simply gives under the pressure exerted by
cl~mps 14- Because t^ne volume of retraction chambers 118 is expanded
accordingly, the pressure of the fluid in chambers 118 and conduit 24 is not
increased substantially.
On the other hand, if the load or workpiece is relatively hard, rods
32 are unable to retract much farther into actuator cylinders 26 when the
predetermined volume of fluid is discharged from chamber 66 of iirst cylinder
58. Thus, because the volume of retraction chamber 118 does not change
substantially, the pressure in retraction chambers 118 and conduit 24 increases.The response of the second source of controlled fluid dischurge 52
to these differences in loads will now be considered. As shown in FIGURE a,
normally closed valve 72 includes a compression chamber la2 adjacent the end of
spool 86 opposite spring 88. Chamber 122 is connected by a conduit 124 to the
clamp side of conduit 74. Thus, when a relatively hard load is clamped, the
increased fluid pressure experienced by conduit 24 is communicated to compres-
sion chamber 122. This pressure exerts a force ~guinst piston 86 that counters
the force of spring 88.
If the load is rigid enough, the pressure developed in chamber 122
will be sufficient to overcome the force exerted by spring 88 and valve 72 will
open. At this point, the reduced diameter portion of piston 86 is aligned with the
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ports in v~lve 72 provided for conduit 74. Once valve 72 is open, the action of
pump 20 c~uses the pressure in the pum~end chamber 78 of cylinder 7~ to
exceed that in the clam~end chamber 8~, driving piston 82 therethrough. In this
manner, the predetermined volume of hydraulic fluid contained in the clam~end
chamber 80 is discharged through conduit 7~ and v~lve 72 to conduit a~ and the
actuator cylinders 26.
If, on the other hand, load 16 had been relatively yielding to the
force applied by cl~mps 14, the pressure in conduit 24 would not have risen
appreciably. In that case, the pressure in compression chamber 12~ of normally
closed valve 72 would have been insufficient to open valve 72. Thus, it is
apparent that the predetermined volume of hydraulic fluid is only supplied to
actuator cylinders a6 when a relatively resistant load is involved. In this
manner, soft loads are protected from the damQge that could result from the
applicQtion of additional force by clamps 14. Because such loads are typically
l 5 relatively light, the initial amount of force established usually provides
clamps 14 with sufficient grasp to allow the load to be easily lifted. For
relatively h~rd loRds, however, additional force can be applied by clamps 14 to
the load without damage and, in fact, this additional force is required if the load
16, which is typic~lly relatively firm and heavy, is to be lifted.
At this point, the operation of an additional source of controlled
fluid discharge 54 will be considered. The normPlly closed valve 92 of the second
discharge means 52 includes a compression chamber 126 located adjacent the end
of piston 106 opposite spring 108. Compression chamber 126 is connected by
conduit 128 to the clamp end of conduit 94. Spring 108 biases piston 106 with
greater orce than the arrangement of valve 72. Thus, valve 92 will open only ifthe discharge of hydraulic fluid from second discharge cylinder 70 into conduit
24 and actuQtor cylinders 26 increases the pressure therein by a predetermined
amount over that required to open valve 72. Again, this requires that the load
exhibit ~ predetermined amount of resistance to the pressure applied by clamps
14 when the second cylinder 70 disch~rges fluid into the actuator cylinders 26.
If the load is of somewh~t intermediate softness, it may give
slightly, allowing rods 8a to retract in cylinders 26. The increased volume of
retraction chambers 118 prevents the pressure in retraction chambers 118,
conduit 24, and compression chamber 126 from increasing enough to open
v~lve 92. In th~t case, cylinder 9G is unable to discharge and no addition~l
pressure is applied to the loAd, thereby protecting the intermediately soft loadfrom possible damage by incre~sed pressure.
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lf the load substan~ially resists the pressure applied by clamps 14
when fluid is ~ischarged by the second cylinder 70, the volume of retraction
chambers 118 remQins relatively unchanged and the pressure therein increases.
In that case, the fluid pressure in compression chamber 126 also increases and,
when it reaches a predetermined level, the force of spring 108 is overcome,
opening vslve 92 and allowing additional cylinder 96 to discharge through con-
duits 94 and 24 to actuator cylinders 26. Thus, in the arrangement shown in
FIGURE a, an additional amount of fluid is introduced into conduit 2~ and
retractiGn chambers 118, causing clamps 14 to apply a greater amount of force
l O to the load.
It will be readily appreciated that a plurnlity of such additional
sources 54 could be employed, each having a normally closed valve ga that opens
at a successively higher pressure. By properly selecting the volume of fluid
contained in the clamp-end chsmber of each cylinder, as well as the operating
pressure of each normally closed valve, the applicQtion of additional pressure by
clamps 14 to the loQd can be substantiaUy any function of the rigidity of the loa~
desired. Thus, the increQSe in pressure applied by clamps 14 to the load can be
substantially directly proportional to the rigidity of the load. In another
arrangement, the first increments in clamp pressure produced after normally
open valve 34 closes are relatively large, with each additional in¢remental
discharge of fluid into the retraction chambers 118 becoming smaller as more
fluid is introduced. This effectively produces a coarse control initi~lly, whichbecomes finer as addition~l pressure is applied by clamps 1~.
It will also be appreciated that other methods of controlling fluid
diseharge to the actuator cylinders 26 can be employed. For example, pressure-
sensitive electric switches can be used to actuate electromechanical valves
controlling the output of the cylinders shown. In addition, a single valve can be
used to repetitively initiate and interrupt the flow of fluid from a single, larger
discharge cylinder, thereby simulating the effect of the multiple controlled
discharge cylinders discussed above.
To prevent the pressure in actu~tor cylinders 26 from exceeding
the maximum safe rating of the cylinders, relief valve $6 provides u path by
which pressurized fluid cnn escape retraction chambers 118 and return to
reservoir 18. As shown in FIGURE 2, chambers 118 are in fluid communication
with Q compression chamber ll9 of valve 56. When the pressure in chumbers 118
renches the maximum safe pressure, the force of spring 114 agninst piston 110 iscounteracted, opening valve 56. In this manner, pressurized fluid in
chambers 118 returns to reservoir 18 through conduit 116.
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13168 ~:l
Once clamps 14 are fully closed, the manually actuated oontrol
valve 2a cnn be switched to Q neutral position C and fluid communication
between pump 20, reservoir 18, and the remainder of system 12 is halted. When
valve 22 is switched to the clamp open position B, the outlet of pump 20 is
connected to a conduit 116 that feeds expansion chambers 130 of actuator
cylinders 26. Thus, the action of pump 20 increases the pressure in the expansion
chambers 130 and, at the same time~ applies this increased pressure to
piston 131 located in check valve 36. Ultimately, piston 131 unseats ball 46,
opening check valve 36~ In this manner, fluid is ~llowed to escape from the
retraction chambers 118 of actuator cylinders 26 and the pressure in the
expansion chambers 130 causes the clamps 14 to open.
While the clamps 14 are opening, fluid is also being introduced into
a group of conduits 132 that feed the clam~end chambers 66, 80, and 102 of the
first, second, and additional discharge cylinders 58, 70, and 90, respectively. The
introduction of this fluid causes the piston in each cylinder to return to its
originDl position for subsequent operation. A check valve 134 placed in the mhinconduit 132 prevents loss of fluid through conduits 132 when the various
cylinders discharge in the clamp-closing mode. A group of conduits 136 provide
return pressure feed paths to the portions of control valves 3~, 56, 72, and 9~,containing the cylindrical springs 42, 88, 108, and 11~. The introduction of fluid
through conduits 136 when valve 22 is opened assists the various springs in
returning their associated valves to their normal position.
It will be understood that the disclosed invention also includes Q
method of automatically controUing the pressure in a fluid-actuated system. In
brief, the method is as follows, with the details being readily appreciable fromthe foregoing discussion. InitiaUy, a predetermined pressure is estsblished in the
retraction chambers 118 of actuator cylinders 26 to provide a desired application
of force by clamps 1~ to the load. When this pressure is reached, a first,
predetermined Yolume of hydraulic fluid is discharged to the retraction chambers118. Only if the load is relatively hard and can withstand the application of
additional force by clàmps 1~ will this discharge of hydraulic fluid increase the
pressure in the retraction chambers 118. In that case, the step of discharging asecond, predetermined volume of fluid to the retraction chambers 118 of
actuator cylinders 26 is perforrned. Agnin, dependent upon the characteristics of
the load to be lifted, additional hydraulic fluid may be introduced to produce
even greater clamping pressure. As will be readily appreciated, pursuant to thismethod, the force applied by clamps 1~ to the load is automatically made
dependent upon the resistance of the load to the application of additional force.
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Additional steps of introducing further predetermined volumes of hydraulie fluidinto the retraction chambers 118 of actuator cylinders 26 ean be provided as
desired .
Those skillçd in the art will recognize that the embodiments of the
5 invention disclosed herein are exemplary in nature and that various changes can
be made therein without departing from the scope and the spirit of the invention.
In this regard, and as was previously mentioned, variations in the amount of
hydraulic fluid discharged by the various cylinders can be used to provide the
desired response of the system to the load characteristics. In addition, numerous
lO arrangements for produeing controlled discharges of hydraulie fluid to the
aetuQtor eylinders can be employed. Because of the above and numerous other
v~riations and modifications that will oeeur to those skilled in the art, the
following elaims should not be limited to the embodiments illustrated and
diseussed herein.
