CA1316871C - Method and apparatus for automatically controlling pressure in fluid-actuated systems - Google Patents
Method and apparatus for automatically controlling pressure in fluid-actuated systemsInfo
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- CA1316871C CA1316871C CA000572844A CA572844A CA1316871C CA 1316871 C CA1316871 C CA 1316871C CA 000572844 A CA000572844 A CA 000572844A CA 572844 A CA572844 A CA 572844A CA 1316871 C CA1316871 C CA 1316871C
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Abstract
METHOD AND APPARATUS FOR AUTOMATICALLY
CONTROLLING PRESSURE IN FLUID-ACTUATED SYSTEMS
Abstract of the Disclosure The invention provides a method and apparatus for controlling the level of clamping pressure applied by a clamp (14) to a load (16). A pump (20), whose output is controlled by a normally open valve (34), establishes an initial level of clamping pressure. Through the use of a number of controllable fluid discharge means (50, 52, 54), this pressure is automatically increased in increments depending upon the resistance of the load to the clamping pressure exerted. In apreferred embodiment, the controllable fluid discharge means include discharge cylinders (58, 70, 90) that contain predetermined volumes of fluid dischargeable by free-floating pistons (62, 82, 92) residing therein. The outputs of the discharge cylinders are controlled by pressure-responsive valves (72, 92) to produce the desired relationship between clamp pressure and load rigidity.
CONTROLLING PRESSURE IN FLUID-ACTUATED SYSTEMS
Abstract of the Disclosure The invention provides a method and apparatus for controlling the level of clamping pressure applied by a clamp (14) to a load (16). A pump (20), whose output is controlled by a normally open valve (34), establishes an initial level of clamping pressure. Through the use of a number of controllable fluid discharge means (50, 52, 54), this pressure is automatically increased in increments depending upon the resistance of the load to the clamping pressure exerted. In apreferred embodiment, the controllable fluid discharge means include discharge cylinders (58, 70, 90) that contain predetermined volumes of fluid dischargeable by free-floating pistons (62, 82, 92) residing therein. The outputs of the discharge cylinders are controlled by pressure-responsive valves (72, 92) to produce the desired relationship between clamp pressure and load rigidity.
Description
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 ~: :
13~L6871 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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131~871 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 - 3a ~
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~1 3 ~ 6 8 7 ~ 62839-1089 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 - 3b -~,.
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1 3 ~ 6 8 7 1 62839-1089 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 ~3~87~
6 62~39~1089 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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6a 62839-1089 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 '~ ' : '' ' '' ' ' ' , 13~ 68~
g 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.
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 ~: :
13~L6871 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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131~871 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 - 3a ~
~-~9 ~, .
~1 3 ~ 6 8 7 ~ 62839-1089 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 - 3b -~,.
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1 3 ~ 6 8 7 1 62839-1089 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 , -., . .
13l687.~
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 ~3~87~
6 62~39~1089 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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131687~
6a 62839-1089 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 .. :
~31~8~
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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 :
~31 687~
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 '~ ' : '' ' '' ' ' ' , 13~ 68~
g 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.
Claims (24)
1. 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 r connected to said actuator cylinder, for producing an initial predetermined pressure in said actuator cylinder; and first 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.
initial pressure establishment means r connected to said actuator cylinder, for producing an initial predetermined pressure in said actuator cylinder; and first 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.
2. The apparatus of claim 1, further comprising 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.
3. The apparatus of claim 2, further comprising at least one additional controllable fluid discharge means, connected to said actuator cylinder, for discharging an additional predeter-mined volume of fluid to said actuator cylinder when the pressure in said actuator cylinder exceeds an additional predetermined pressure, said additional volume of fluid and said additional pressure being separately determined for each said additional fluid discharge means employed.
4. The apparatus of claim 2, wherein said clamp is closably actuated by a pair of clamp actuator cylinders connected to said first and second means.
5. The apparatus of claim 2, further comprising a pressure-relief valve for allowing said fluid in said actuator cylinder to escape if the pressure in said actuator cylinder exceeds a predetermined relief pressure.
6. 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:
pressure establishment means for transferring fluid to said actuator cylinder;
an initial conduit connecting said pressure establish-ment 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 means 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 predetermined volume of said fluid to said actuator cylinder when said initial predetermined pressure in said actuator cylinder is reached; 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.
pressure establishment means for transferring fluid to said actuator cylinder;
an initial conduit connecting said pressure establish-ment 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 means 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 predetermined volume of said fluid to said actuator cylinder when said initial predetermined pressure in said actuator cylinder is reached; 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.
7. The apparatus of claim 6, wherein said valve means comprises a normally open valve and wherein said first fluid discharge means comprises:
a first conduit, connected in parallel to said normally open valve; and a first discharge cylinder interrupting said first conduit between said pressure establishment means and said actuator cylinder, said first cylinder including a first free floating piston disposed between a pressure establishment means-end of said first cylinder and an actuator end, said pressure establishment means introducing fluid into said pressure establish-ment means-end of said first cylinder and forcing said first piston toward said actuator end of said first cylinder when said normally open valve closes, discharging said first volume of said fluid to said actuator cylinder.
a first conduit, connected in parallel to said normally open valve; and a first discharge cylinder interrupting said first conduit between said pressure establishment means and said actuator cylinder, said first cylinder including a first free floating piston disposed between a pressure establishment means-end of said first cylinder and an actuator end, said pressure establishment means introducing fluid into said pressure establish-ment means-end of said first cylinder and forcing said first piston toward said actuator end of said first cylinder when said normally open valve closes, discharging said first volume of said fluid to said actuator cylinder.
8. The apparatus of claim 7, wherein said second fluid discharge means comprises:
a second conduit, connected in parallel to said normally open valve;
a second discharge cylinder interrupting said second conduit between said pressure establishment means and said actuator cylinder, said second cylinder including a second free-floating piston disposed between a pressure establishment means-end of said second cylinder and an actuator end; and a normally closed valve interrupting said second conduit between said second discharge cylinder and said actuator cylinder, said pressure establishment means introducing fluid into said pressure establishment means-end and forcing said second piston toward said actuator end of said second cylinder when said normal-ly closed valve opens, discharging said second volume of said fluid to said actuator cylinder, said normally closed valve open-ing when the pressure in said actuator cylinder increases by said predetermined amount.
a second conduit, connected in parallel to said normally open valve;
a second discharge cylinder interrupting said second conduit between said pressure establishment means and said actuator cylinder, said second cylinder including a second free-floating piston disposed between a pressure establishment means-end of said second cylinder and an actuator end; and a normally closed valve interrupting said second conduit between said second discharge cylinder and said actuator cylinder, said pressure establishment means introducing fluid into said pressure establishment means-end and forcing said second piston toward said actuator end of said second cylinder when said normal-ly closed valve opens, discharging said second volume of said fluid to said actuator cylinder, said normally closed valve open-ing when the pressure in said actuator cylinder increases by said predetermined amount.
9. The apparatus of claim 8, further comprising at least one additional controllable fluid discharge means, connected to said actuator cylinder, for discharging an additional predetermined volume of fluid to said actuator cylinder when the pressure in said actuator cylinder exceeds an additional predetermined pres-sure, said additional volume of fluid and said additional pressure being separately determined for each said additional fluid discharge means employed.
10. The apparatus of claim 9, wherein said additional fluid discharge means comprises:
an additional conduit, connected in parallel to said normally open valve;
an additional discharge cylinder interrupting said additional conduit between said pressure establishment means and said actuator cylinder, said additional cylinder including an additional free-floating piston disposed between a pressure establishment means-end of said additional cylinder and an actua-tor end; and an additional normally closed valve interrupting said additional conduit between said additional discharge cylinder and said actuator cylinder, said pressure establishment means intro-ducing fluid into said pressure establishment means-end and forcing said additional piston toward said actuator end of said additional cylinder when said additional normally closed valve opens, discharging said additional volume of said fluid to said actuator cylinder, said additional normally closed valve opening when the pressure in said actuator cylinder exceeds said additional pressure.
an additional conduit, connected in parallel to said normally open valve;
an additional discharge cylinder interrupting said additional conduit between said pressure establishment means and said actuator cylinder, said additional cylinder including an additional free-floating piston disposed between a pressure establishment means-end of said additional cylinder and an actua-tor end; and an additional normally closed valve interrupting said additional conduit between said additional discharge cylinder and said actuator cylinder, said pressure establishment means intro-ducing fluid into said pressure establishment means-end and forcing said additional piston toward said actuator end of said additional cylinder when said additional normally closed valve opens, discharging said additional volume of said fluid to said actuator cylinder, said additional normally closed valve opening when the pressure in said actuator cylinder exceeds said additional pressure.
11. The apparatus of claim 10, further comprising a pressure-relief valve for allowing said fluid in said actuator cylinder to return to said reservoir if the pressure in said actuator cylinder exceeds a predetermined relief pressure.
12. 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 controllable 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.
first controllable 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.
13. 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 controllable fluid discharge means for discharging a first predetermined volume of said fluid to said actuator cylinder, said first fluid discharge means comprising a first discharge cylinder having a first free-floating piston disposed between a source-end of said first cylinder and an actuator 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 volume of fluid to said actuator cylinder increases the pressure in said actuator cylinder by a predetermined amount.
first controllable fluid discharge means for discharging a first predetermined volume of said fluid to said actuator cylinder, said first fluid discharge means comprising a first discharge cylinder having a first free-floating piston disposed between a source-end of said first cylinder and an actuator 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 volume of fluid to said actuator cylinder increases the pressure in said actuator cylinder by a predetermined amount.
14. The apparatus of claim 13, wherein said second fluid discharge means comprises:
a second discharge cylinder having a second free-floating piston disposed between a source-end of said second cylinder and an actuator end; and a normally closed valve controlling the discharge of said second volume of fluid from said second cylinder, said source being for introducing fluid into said source-end and forc-ing said second piston toward said actuator end of said second cylinder when said normally closed valve opens, discharging said second volume of fluid to said actuator cylinder, said normally closed valve opening when the pressure in said actuator cylinder increases by said predetermined amount.
a second discharge cylinder having a second free-floating piston disposed between a source-end of said second cylinder and an actuator end; and a normally closed valve controlling the discharge of said second volume of fluid from said second cylinder, said source being for introducing fluid into said source-end and forc-ing said second piston toward said actuator end of said second cylinder when said normally closed valve opens, discharging said second volume of fluid to said actuator cylinder, said normally closed valve opening when the pressure in said actuator cylinder increases by said predetermined amount.
15. The apparatus of claim 14, further comprising at least one additional controllable fluid discharge means, connected to said actuator cylinder, for discharging an additional predetermined volume of fluid to said actuator cylinder when the pressure in said actuator cylinder exceeds an additional predetermined pres-sure, said additional volume of fluid and said additional pressure being separately determined for each said additional means employed.
16. The apparatus of claim 15, wherein said additional fluid discharge means comprises:
an additional discharge cylinder having an additional free-floating piston disposed between a source-end of said addi-tional cylinder and an actuator end; and an additional normally closed valve controlling the discharge of said additional volume of fluid from said additional cylinder, said source being for introducing fluid into said source-end and forcing said additional piston toward said actuator end of said additional cylinder when said additional normally closed valve opens, discharging said additional volume of fluid to said actuator cylinder, said additional normally closed valve opening when the pressure in said actuator cylinder exceeds said additional pressure.
an additional discharge cylinder having an additional free-floating piston disposed between a source-end of said addi-tional cylinder and an actuator end; and an additional normally closed valve controlling the discharge of said additional volume of fluid from said additional cylinder, said source being for introducing fluid into said source-end and forcing said additional piston toward said actuator end of said additional cylinder when said additional normally closed valve opens, discharging said additional volume of fluid to said actuator cylinder, said additional normally closed valve opening when the pressure in said actuator cylinder exceeds said additional pressure.
17. The apparatus of claim 16, further comprising a pressure-relief valve for allowing said fluid in said actuator cylinder to return to said source if the pressure in said actuator cylinder exceeds a predetermined relief pressure.
18. The apparatus of claim 13, further comprising at least one additional controllable fluid discharge means, connected to said actuator cylinder, for discharging an additional predeter-mined volume of fluid to said actuator cylinder when the pressure in said actuator cylinder exceeds an additional predetermined pressure, said additional volume of fluid and said additional pressure being separately determined for each said additional means employed.
19. The apparatus of claim 13, further comprising a pressure-relief valve for allowing said fluid in said actuator cylinder to return to said source if the pressure in said actuator cylinder exceeds a predetermined relief pressure.
20. 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, predetermined 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.
discharging a first, predetermined 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.
21. The method of claim 20, further comprising the step of producing an initial predetermined pressure in said actuator cylinder before said step of discharging said first volume of fluid to said actuator cylinder.
22. The method of claim 21, further comprising the step of discharging at least one additional, predetermined volume of fluid to said actuator cylinder when the pressure in said actuator cylinder exceeds an additional, predetermined pressure, said additional volume of fluid and said additional pressure being separately determined for each said step of discharging an additional volume of fluid.
23. The method of claim 22, further comprising the step of relieving the pressure in said actuator cylinder when said pressure in said actuator cylinder exceeds a predetermined relief pressure.
24. The method of claim 20, further comprising the step of discharging at least one additional, predetermined volume of fluid to said actuator cylinder when the pressure in said actuator cylinder exceeds an additional, predetermined pressure, said additional volume of fluid and said additional pressure being separately determined for each said step of discharging said additional volume of fluid.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000572844A CA1316871C (en) | 1988-07-22 | 1988-07-22 | Method and apparatus for automatically controlling pressure in fluid-actuated systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000572844A CA1316871C (en) | 1988-07-22 | 1988-07-22 | Method and apparatus for automatically controlling pressure in fluid-actuated systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1316871C true CA1316871C (en) | 1993-04-27 |
Family
ID=4138425
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000572844A Expired - Fee Related CA1316871C (en) | 1988-07-22 | 1988-07-22 | Method and apparatus for automatically controlling pressure in fluid-actuated systems |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1316871C (en) |
-
1988
- 1988-07-22 CA CA000572844A patent/CA1316871C/en not_active Expired - Fee Related
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