EP2699804A1

EP2699804A1 - Synchronized lifting apparatus

Info

Publication number: EP2699804A1
Application number: EP12859424.9A
Authority: EP
Inventors: Frantz D. Stanford
Original assignee: Actuant Corp
Current assignee: Enerpac Tool Group Corp
Priority date: 2011-04-21
Filing date: 2012-04-10
Publication date: 2014-02-26
Also published as: EP2699804A4; WO2013095693A1; CN103562563A; AU2012355968A1

Abstract

A synchronous lifting system with single-rod, single-acting hydraulic cylinders controlled by parallel-connected lift valves having two fluid passages. Hydraulic fluid for extending the actuators is delivered by a hydraulic supply system alternating between the two passages. Each time the supply circuit alternates passages, a fixed volume of hydraulic fluid is transferred by the lift valves to the cylinders causing the rods to lift a proportionate amount. All of the rods extend by approximately the same increment each time the supply circuit alternates passages. Because the rods all extend the same increment each cycle, the load is lifted evenly and the need for height sensors or transducers is eliminated.

Description

SYNCHRONIZED LIFTING APPARATUS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 61/477,931, filed April 21, 201 1, the disclosure of which is hereby incorporated by reference for all purposes.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

FIELD OF THE INVENTION

[0003] This invention relates to the lifting of large structures such as slabs, foundations, bridges, buildings and other structures using a number of hydraulic actuators in a synchronized manner. As used herein, "lifting" includes pushing, hoisting, and all other applications in which hydraulic actuators are extended or retracted synchronously.

BACKGROUND OF THE INVENTION

[0004] Hydraulic systems for lifting structures such as slabs, foundations, bridges and buildings, ships, barges, oil platforms, or large transformers are known. The task is straightforward when the load of the structure is evenly distributed and when some flexing is allowed. Conversely, lifting a structure that cannot be flexed or twisted or with uneven weight distribution, such as a slab poured on grade, is a somewhat more difficult operation. Without some control intervention, hydraulic flow to the lifting actuators takes the path of least resistance, resulting in the lightest portion of the load coming up first. This displacement differential may create internal stresses in the structure being lifted, increasing the likelihood of causing damage to the structure. In addition, the displacement differential can create instability during the lift, such that the lift set up could collapse.

[0005] In order to lift inflexible structures, or those with uneven weight distribution, without causing damage, a number of hydraulic systems, including manually, mechanically or electronically operated systems, have been designed with synchronous lift control capabilities to prevent twisting or uneven loading during a lifting operation. However, these systems, depending on the type, are typically difficult to operate, complex to assemble, and/or very expensive. As a result, synchronized lifting of large structures is only used for high-level and complex lifting projects.

[0006] In response to the cost-prohibitive nature of existing hydraulic synchronized lifting systems, a low cost solution, i.e., a positive-displacement flow-divider, or PDFD was developed. The PDFD, however, is designed to lift at a reduced operating pressure and limited to four segments or less, typically. Therefore, it is desirable to have other inexpensive yet more functional solutions that provide for synchronized lifting of large and uneven structures.

SUMMARY OF THE INVENTION

[0007] The present invention alleviates these needs by providing a simple, cost effective synchronized lifting system that is almost unlimited in the number of lift-points that can be used. The invention provides a low-cost, minimally controlled solution for lifting uneven loads with little technical expertise needed by the operator.

[0008] The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 is a schematic view of a hydraulic circuit including a synchronous valve, a lifting cylinder, and a hydraulic supply system in accordance with one aspect of the present invention;

[0010] Fig. 2 is a graphical representation of a synchronized lifting system utilizing a plurality of the synchronous valves of Fig. 1 ; and

[0011] Fig. 3 is a logic diagram for the hydraulic supply system of Fig. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] The present invention provides synchronized, incremental lifting of a slab-like structure by a plurality of interconnected hydraulic lift actuators. The hydraulic and control circuits for a synchronous lift valve and a synchronous lifting system are illustrated in the figures. As shown in Fig. 1, embodiments of a synchronous lift valve 10, single-acting lift cylinder 12, and fluid supply system 14 are schematically represented. The lift valve 10 incrementally delivers a fixed volume of pressurized incompressible fluid, such as hydraulic fluid, to the lift cylinder 12 as further discussed below. As shown in Fig. 2, one embodiment of a synchronized lift system 16 includes a plurality of interconnected lift valves 10, a plurality of lift cylinders 12 connected to a separate lift valve 10, and the fluid supply system 14 supplying pressurized fluid, i.e., an excitation input, to all of the lift valves 10. The term "hydraulic" and "fluid" are used interchangeably, though the term "fluid" is not limited to just hydraulic fluid.

[0013] Referring initially to Fig. 1, the synchronous lift valve 10 is a compact assembly designed to be contained within a manifold 17 and installed in a supply line 18 between the lift cylinder 12 and the pressurized fluid supply 14. The synchronous lift valve 10 includes two distinct but interconnected fluid supply passages, first passage 20 and second passage 22.

[0014] The first and second passages 20, 22 begin at a pair of supply ports 24, 26 formed in the assembly 17, respectively, extend through a number of components contained therein, and end at a single outlet port 28. Each fluid passage 20, 22 includes an inlet line, 30, 32 that originates at the respective port 24, 26 and passes through a manually-operated block valve, i.e., on/off valve 34. Each inlet line 30, 32 further passes through a first check valve 36, 38, respectively, and into opposite ends of a fixed incremental volume device, or fluid metering cylinder 40.

[0015] The fluid metering cylinder 40 includes a sealed linear reciprocal piston 42 dividing the cylinder 40 into left, or first, and right, or second, variable-volume pressure chambers 44, 46, with no appreciable fluid flow past the piston 42. Each fluid passage 20, 22 further includes a respective outlet line 48, 50 that begins at the cylinder 40 and passes through a pilot-operated check valve 52, 54, respectively. Each outline line 48, 50 further passes through a second check valve 56, 58 and converges into a single supply line 60 that ends at the outlet port 28. The outlet port 28 is in fluid communication with a lower chamber 64 of the hydraulic lift cylinder 12 via the supply line 18.

[0016] The first check valves 36, 38, and second check valves 56, 58 operate as one-way passive barriers to selectively open and close the passages 20, 22 depending on the direction of fluid flow therein. The pilot-operated check valves 52, 54 operate as conventional check valves to prevent the flow of fluid from the metering cylinder 40 into the outlet lines 48, 50. However, these valves 52, 54 perform a different function when acted on by a pilot, i.e., a separate fluid pressure source. Specifically, when the inlet line 30 of the first passage 20 is pressurized, fluid is directed through a line 62 to open the valve 54 and permit two-way fluid flow therethrough. Similarly, by separate operation of the inlet line 32 of the second passage 22, fluid is directed through a line 64 to open valve 52 and permit two-way flow therethrough. When there is no fluid pressure within inlet line 30, the pilot function is removed and valve 54 closes to provide a passive barrier in the second passage 22. Similarly, when there is no fluid pressure within inlet line 32, the pilot function is removed and valve 52 closes to provide a passive pressure barrier in the first passage 20.

[0017] The metering cylinder 40 is operated to provide a fixed, or metered, amount of fluid to the lift cylinder 12 resulting in a proportionate amount of lift in a manner explained below. Further components of the synchronous lift valve 10 include a fluid return passage 66 having a block valve 68 with flow restrictor 70, an auxiliary inlet port 72 that can be used to add more hydraulic fluid to the lift cylinder 12, an auxiliary inlet port check valve 74, a pressure relief valve 76, and a pressure gauge 80.

[0018] The lift cylinder 12 includes a cylinder barrel 82 and a displaceable piston 84 contained therein. The piston 84 is connected to a piston rod 86 extending upwardly and outwardly from the barrel 82. A lower (bore side) chamber 88 and an upper (rod side) chamber 90 are formed within the barrel 82 on opposite sides of the piston 84. As is well known, hydraulic fluid delivered to the lower chamber 88 causes an upward force to be applied against the piston 84. A spring 92 situated within the upper chamber 90 biases the piston 84 in a downward direction. Referring also to Fig. 2, the rod 86 lifts a slab 94 or a support plate such that when the upward force is greater than the downward forces (including the weight of the slab 94), the piston 84 translates upward within the barrel 82 and the piston rod 86 raises the slab 94. A reaction point 96 (see Fig. 2) is provided by a mechanical pier, piling, or other stable foundation in the ground. Fig. 2 is a schematic illustration; typically the pier 96 is below the slab 94, the cylinder 12 is supported above the slab 94 by a lift structure (not shown) that is supported on the pier 96, and the lift structure couples the piston 84 and the slab 94 so the movement of the piston 84 is translated to the slab 94.

[0019] As foundation, slab and bridge lifting applications usually are high tonnage lifts, it is desirable and usual in such applications that the lift cylinder 12 used for such lifts is a high pressure actuator capable of pressures as high as 10,000 psi. The rod 86 is sized accordingly to bear the load for particular applications.

[0020] The synchronous lift valve 10 is supplied with pressurized hydraulic fluid by the hydraulic supply system 14 that includes a pump 98, a four- way/two-position solenoid, or fluid supply solenoid valve 100, and a pressure control circuit 102. The pump 98 in the embodiment shown is capable of delivering hydraulic fluid at pressures up to 10,000 PSI. As shown in Fig. 1 , when the fluid supply solenoid valve 100 is in the illustrated first, de-energized position, pressurized hydraulic fluid is directed to the first port 24 of the lift valve 10 while the second port 26 is in fluid communication with a fluid reservoir 104. A pressure actuated switch 106 is connected to the output of the pump 98. When the fluid pressure reaches a certain threshold, i.e., a maximum set pressure, for example, 8,000 PSI, switch 106 closes, energizing a two-position latching relay 108 which in turn closes a set of normally open contacts 1 10. Consequently, the supply solenoid valve 100 becomes energized and alternates to a second, energized position.

[0021] When the solenoid valve 100 is energized, pressurized hydraulic fluid is directed to the second port 26 of the lift valve 10 and the first port 24 is in fluid communication with the reservoir 104. Pressure switch 106 opens again when the valve 100 shifts, since the pressure drops below the set limit. The supply solenoid valve 100 remains energized by action of the relay 108 which remains latched until the pressure switch 106 is closed again. As shown in Fig. 3, during normal operation, the solenoid valve 100 alternates between the energized and de- energized state in a cycle having constant and equal intervals. In other words, the hydraulic supply system 14 alternately delivers pressurized hydraulic fluid to the first and second ports 24, 26, switching between the two ports 24, 26 each time the pressure switch 106 is momentarily closed. As an alternative to the supply system 14, a pump with a programmable control could be used, or the system could be manually operated so as to lift in a series of increments.

[0022] Specifically referring to Fig. 2, one embodiment of a synchronized lifting system 16 of the present invention includes a plurality of synchronous valves 10 and corresponding lift cylinders 12 spaced apart to lift the slab 94 in a known manner. Each lift cylinder 12 is connected to and controlled by a separate lift valve 10. The hydraulic supply system 14 delivers pressurized hydraulic fluid to each of the valves 10 via a set of supply lines 1 12, 1 14. As shown, the lift valves 10 are plumbed together in parallel via the supply lines 112, 1 14. Each of the first ports 24 of the system 16 are in fluid communication with each other while each of the second ports 26 are likewise in fluid communication with each other. The outlet port 28 of each synchronous valve 10 is only in fluid communication with the associated lift cylinder 12 via separate supply lines 18.

[0023] In operation, the on/off valve 34 of the lift valve 10 is manually opened and the return valve 68 is manually closed. The supply solenoid valve 100 is initially in the de-energized position. The pump 98 is turned on and pressurized hydraulic fluid is delivered via supply line 1 12 to the first port 24 of the lift valve 10, as well as to all the other first ports 24 connected in parallel to the supply line 1 12. A typical hydraulic fluid pressure curve 1 16 is shown in Fig. 3. The hydraulic fluid flows into the first passage 20 through the first port 24, on/off valve 34, first check valve 36, and into the left chamber 44 of the metering cylinder 40.

[0024] As the pressurized fluid enters the left chamber 44, the piston 42 is forced to move through its stroke and displaces the entire volume of hydraulic fluid, i.e., a fixed volume shot, from the right chamber 46 into the outlet line 50 of the second passage 22. The pilot- operated valve 54 is open due to the presence of pressurized fluid in the inlet line 30 of the first passage 20. Thus the displaced fluid from the right chamber 46 flows through the valve 54, through the second check valve 58 and into the lower chamber 88 of the lift cylinder 12. Each metered volume of fluid delivered to the cylinder 12 results in a proportionate amount, or increment, of vertical movement, or lifting, of the piston 84, rod 86 and slab 94 because of the incompressible nature of the fluid. Each parallel-connected lift valve 10 in the synchronous lift system 16 acts in an identical manner and causes each associated lift cylinder 12 to raise the slab 94 up by the same incremental amount.

[002S] When the hydraulic fluid reaches the pressure set point, pressure switch 106 momentarily closes, activating the relay 108 which in turn energizes the supply solenoid valve 100. The pressure limit set point is significantly higher than the highest pressure required by any of the cylinders 12 to lift its load, so all of the cylinders 12 have extended by the volume and fluid displaced into them from the right chamber 46 and have stopped extending before the pressure limit set point is reached. Therefore, they have all extended the same amount, although not necessarily at the same rate. For as long as the solenoid valve 100 is energized, hydraulic fluid is directed from the pump 98 to the second port 26. As shown in Fig. 3, the pressure of the supplied hydraulic fluid initially drops when the solenoid valve 100 is energized but immediately begins to recover. As discussed above, regardless of the subsequent drop in pressure in the fluid supply system 14, which opens switch 106, the solenoid valve 100 remains energized by operation of the latching relay 108.

[0026] Hydraulic fluid is thus directed into the second passage 22 through the second port 26, on/off valve 34, first check valve 38, and into the right chamber 46 of the metering cylinder 40. The fluid accumulating in the right chamber 46 causes the piston 42 to travel through a reverse stroke toward the left as viewed in Fig. 1, having been moved to the right on the previous stroke, expelling the volume of fluid from the left chamber 44 into the outlet line 48 of the first passage 20. The fluid is forced through the pilot-operated check valve 52 (which is open because of the presence of pressurized fluid in line 32), second check valve 56, and into the lower chamber 88 of the lift cylinder 12. This additional volume of fluid causes the piston 84, rod 86, and slab 94 to be raised by another increment and then stop when the associated piston 42 stops. The fluid pressure continues to build until it reaches the set pressure when the switch 106 closes. The relay 108 unlatches and contacts 1 10 open, thereby de-energizing the solenoid valve 100. The solenoid valve 100 returns to the de-energized position and hydraulic fluid is once again directed to the first passage 20. Due to the pressure drop, pressure switch 106 subsequently opens. The cycle of delivering a metered amount of hydraulic fluid to the cylinder 12 in this manner is repeated over and over until the slab 94 has been lifted to a desired height or the rods 86 have been extended to their full extension.

[0027] To lower the rods 86 after being decoupled from the slab 94, on/off valve 34 is closed, the lift/lower block valve 68 is opened, and the solenoid valve 100 is energized. Hydraulic fluid is pushed out of the cylinder barrels 82 by the downward forces including the spring 92 decompressing force against the piston 84. The fluid is directed through the outlet port 28 and into the return line 60. The fluid is prevented from flowing into the metering cylinder 40 by the second set of check valves 56, 58. The fluid passes through the flow restrictor 70, through the energized solenoid valve 100, and into the reservoir 104. The flow restrictor 70 restricts flow to provide a more slow controlled descent or retraction of the cylinders 12.

[0028] By plumbing each synchronous valve 10 of the synchronous lift system 16 in parallel, the pressure of the hydraulic fluid delivered to each lift cylinder 12 is, for all practical purposes, the same. In other words, all cylinders 12 will be pressurized at the same rate, regardless of load. However, not all of the rods 86 will necessarily be lifted at the same time. Depending on the weight of the portion of the slab 94 supported by the rod 86, some lift cylinders 12 will require a greater fluid pressure to effect a lift. The cylinders 12 requiring a lower pressure to be extended will be extended first or at a higher rate, with the cylinders 12 requiring a higher pressure following. However, regardless of the rate of lifting during each extension, each rod 86 is only extended one increment per cycle and all of them are extended one increment. The increment is determined by the volume displaced from the metering cylinder 40 on each stroke. As such, the difference in height between any two rods 86 is never more than a single increment and never for longer than the time it takes for the pump 98 to reach a pressure sufficient to cause any slow or heavily loaded rods 86 to be extended. Then after they have all extended and all of the pistons 42 have stopped, the set pressure limit (e.g., 8,000 psi) is quickly reached and a new stroke cycle is started. Thereby, the rods of all of the cylinders are extended in a series of successive increments until the desired lift elevation is reached, at which time the valve 34 is turned off to hold the load at that elevation while it is secured with bolts or other means to support it at that elevation, so the lifting cylinders, valves and other lifting system components can be removed and reused.

[0029] In one example, the synchronized lifting system 16 is used on a slab 94 with an uneven weight distribution. The metering cylinder 40 and barrel 82 are sized such that each metered volume of hydraulic fluid displaced from the metering cylinder 40 causes the piston 84 and rod 86 to be lifted by 0.125". A lift cylinder 12 under a lighter portion of the slab 94 may need 1,000 PSI of hydraulic pressure to lift the associated rod 86, while another lift cylinder 12 under a heavier portion may need 2,000 PSI to lift the associated rod 86. When the pump 98 is turned on, the pressure of the hydraulic fluid eventually reaches 1,000 PSI, at which point the rod 86 under the lighter portion is lifted. The pressure continues to increase until reaching 2,000 PSI, at which point the rod 86 under the heavier portion is lifted. As previously described, for each cycle, the hydraulic fluid pressure builds until reaching the pressure set-point at which point all of the rods 86 will have been raised by an increment of 0.125". If, during or at the end of lifting not all of the cylinders are at the same height due to some small error, or to make desired adjustments, a secondary pump may be hooked up to the auxiliary inlet port 72 to make up the difference. Another way to do this, if one point is too high, is to turn off the valve 34 at that point and raise the other lift points.

[0030] The invention thereby provides a synchronized hydraulic lifting system with minimal electronic controls to understand, fail or learn, no height sensors needed, that can be used with all identical actuators, and in which the attachment points, i.e., the ports 24 and 26, can be polarized (i.e., mechanical connectors used so that each first port 24 can only be connected to another first port 24 and vice versa) to facilitate assembly. Further, this system can be used in the lifting of slab foundations, houses and similar structures that are made of materials that do not allow them to be twisted or flexed significantly without causing damage.

[0031] Additional embodiments have been contemplated regarding the slightly compressible nature of hydraulic fluid, or that hydraulic fluid may become aerated and become further compressible. If the fluid is slightly compressible and there are different loads on each lift point, lift point to lift point height differences, i.e., error, may occur during a lifting operation. Therefore, one contemplated embodiment of a synchronous lift system 16 uses a fluid with a very low compressibility (i.e., high bulk modulus) and isolates that fluid from the pump 98 by attaching a cylinder (not shown) with a floating piston to each port 24, 26 of each lift valve 10. The fluid with very low compressibility (e.g., glycol or similar) would be contained within the valve 10 by the floating piston while the supply system other side of the floating piston would have standard hydraulic oil. With such an arrangement, aeration would be eliminated and the compressibility of the fluid in the lift valve 10 could be reduced by a factor of two or three.

[0032] Preferred embodiments of the invention have been described in considerable detail. Many modifications and variations to the preferred embodiments described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiments described.

Claims

I claim:

1. A synchronous lifting system having a plurality of lift cylinders distributed about a load at lifting points to raise each lifting point of the load by approximately the same increment as the increments of the other lifting points, the system comprising:

a plurality of lift valves, each lift valve having a first port in fluid communication with a first variable volume chamber and a second port in fluid communication with a second variable volume chamber;

a plurality of lift cylinders, each of said lift cylinders being in fluid communication with an associated one of said lift valves;

wherein each of said first and second variable volume chambers of said lift valves are in fluid communication with a load port of said associated lift cylinder such that rods of the plurality of lift cylinders extend by generally the same increment when a fluidic pressure is applied to the plurality of lift valves.

2. A synchronous lifting system as in claim 1 , wherein each of the lift valves includes an outlet port.

3. A synchronous lifting system as in claim 2, wherein each of the lift valves includes a first pilot-operated check valve between the first variable volume chamber and the outlet port that prevents fluid in said first variable volume chamber from flowing to said lift cylinder when there is no pressure between the second port and the second variable volume chamber.

4. A synchronous lifting system as in claim 3, wherein each of the lift valves includes a second pilot-operated check valve between the second variable volume chamber and the outlet port that prevents fluid in said second variable volume chamber from flowing to said lift cylinder when there is no pressure between the first port and the first variable volume chamber.

5. A synchronous lifting system as in claim 1 , further comprising controls that repetitively alternate between supplying pressure to the first variable volume chambers and supplying pressure to the second variable volume chambers so as to extend the rods of the plurality of lift cylinders in a series of successive increments.

6. A method of lifting a load including the steps of:

distributing a plurality of hydraulic lift actuators at lifting points positioned about the load;

connecting each of the plurality of actuators to an associated one of a plurality of lift valves, each lift valve having a first, a second and a third port and providing a metered output from said third port when a fluid supply is connected to said first and second ports;

connecting the plurality of lift valves to one another in parallel such that all of said first ports are in fluid communication with each other and all of said second ports are in fluid communication with each other;

introducing pressurized fluid to the parallel-connected first supply ports so as to cause the rods of the actuators to extend by approximately the same increment;

introducing pressurized fluid to the parallel-connected second supply ports so as to cause the rods of the actuators to extend by approximately the same increment; and

alternating the introduction of said pressurized fluid between the first and second parallel-connected supply ports.

7. A synchronous lift system for extending a plurality of hydraulic actuators in unison, comprising:

a plurality of hydraulic actuators, each said actuator having a cylinder barrel and a piston in the cylinder barrel that defines at least one sealed variable volume chamber in the cylinder barrel;

a plurality of valves, one said valve associated with each said hydraulic actuator, each said valve comprising a fixed incremental volume device that in response to an excitation input to the valve, outputs to the actuator a fixed volume shot of hydraulic fluid to extend the actuator a certain amount in accordance with the volume of the shot, wherein the valves are connected to receive the excitation input at the same time after each valve has output the shot of fluid to its associated actuator; and

a pressure supply connected to the valves to provide a series of excitation inputs to the valves so as to incrementally and repetitively extend the actuators.

8. A synchronous lift system as in claim 7, wherein the fixed incremental volume device includes a first variable volume chamber and a second variable volume chamber that varies in volume inversely proportional to the volume of the first variable volume chamber such that introducing fluid from the pressure supply to the first variable volume chamber presses the fixed volume shot of hydraulic fluid out of the second variable volume chamber to the actuator and introducing fluid from the pressure supply to the second variable volume chamber presses the fixed volume shot of hydraulic fluid out of the first variable volume chamber to the actuator.

9. A synchronous lift system as in claim 8, wherein the series of fixed volume shots of hydraulic fluid are delivered to the actuator by alternately introducing fluid to the first variable volume chamber and second variable volume chamber.

10. A synchronous lift system as in claim 9, wherein each shot of fluid flows from a variable volume chamber through a pilot pressure operated valve.

11. A synchronous lift system as in claim 10, wherein each valve has a first supply port and a second supply port, each of which are connected to the pressure supply and which are alternately pressurized and vented to tank pressure so as to provide the series of excitation inputs to the valve.

12. A synchronous lift system as in claim 11, wherein the pressure supply includes a latching relay that holds supply pressure on one of the supply ports and tank pressure on the other of the supply ports until a supply pressure limit is reached, and then holds tank pressure on the one of the supply ports and supply pressure on the other of the supply ports until the supply pressure limit is reached again, at which time it switches back and the cycle continues.

13. A synchronous lift system as in claim 12, wherein the pressure supply further includes a pressure operated switch that triggers the latching relay when the supply pressure limit is reached.

14. A synchronous lift system as in claim 7, wherein each of the plurality of valves further comprises an auxiliary port through which fluid under pressure can be introduced into the associated actuator.