Apparatus and methods for the control of hydraulic actuators

Abstract

Methods of controlling an actuator during operation using a hydraulic circuit, and related apparatus, are described. The circuit has a first path section along which fluid is supplied to a first chamber of the actuator using a first valve and a second path section along which fluid is extracted from a second chamber of the actuator using a second valve. Pressure data associated with a pressure of the fluid supplied to the first side of the actuator are obtained, a pilot pressure pPilot is produced based on the data and the first and second valves are configured based on the pilot pressure pPilot.

Claims

1. A method of controlling an actuator during operation using a hydraulic circuit, the circuit comprising a pressure compensating valve, a counterbalance valve, a load-sensing directional control valve, a first path section along which a hydraulic fluid is supplied to a first chamber of the actuator via the pressure compensating valve, the hydraulic fluid being supplied to the first chamber via the load-sensing directional control valve, and a second path section along which the hydraulic fluid is extracted from a second chamber of the actuator via the counterbalance valve, the method comprising the steps of: (a) obtaining pressure data associated with a pressure of the hydraulic fluid supplied to a first side of the actuator; (b) producing a pilot pressure pPilot in a control fluid based on the pressure data; (c) configuring the pressure compensating valve using the pilot pressure pPilot; and (d) configuring the counterbalance valve using the pilot pressure pPilot.

2. A method as claimed in claim 1, wherein the pressure data comprises a signal of the pressure in the hydraulic fluid supplied to the first chamber.

3. A method as claimed in claim 1, wherein the obtained pressure data are first pressure data, and the method further comprises processing the first pressure data to produce second pressure data, wherein the pilot pressure pPilot is produced based upon the second pressure data.

4. A method as claimed in claim 3, wherein at least one component from the first pressure data is preserved in the produced second pressure data.

5. A method as claimed in claim 3, wherein the step of processing the first pressure data to obtain the second pressure data comprises filtering the first pressure data.

6. A method as claimed in claim 5, wherein the step of filtering comprises applying a low-pass filter to the first pressure data.

7. A method as claimed in claim 3, which further comprises generating a control signal uProp based on the second pressure data, and passing the control signal uProp to a first valve to produce the pilot pressure pPilot for configuring both of the pressure compensating valve and the counterbalance valve.

8. A method as claimed in claim 7, wherein the first valve is operable to configure a valve control path for adjusting a pressure in the control fluid in the path.

9. A method as claimed in claim 7, which further comprises measuring the produced pilot pressure pPilot, comparing the measured pilot pressure with the second pressure data, and updating the control signal uProp in dependence upon the comparison.

10. A method as claimed in claim 1, wherein the obtained pressure data are first pressure data, and the method further comprises processing the first pressure data to determine at least one set pressure pSet for determining the pilot pressure pPilot.

11. A method as claimed in claim 1, wherein the pressure compensating valve is operable for adjusting a pressure of the fluid in the first path section.

12. A method as claimed in claim 1, wherein the counterbalance valve is operable for resisting undesired movement of the actuator.

13. A method as claimed in claim 1, wherein the pressure compensating valve and the counterbalance valve are configured to be operable to maintain an actuator speed that is independent of external disturbances on the actuator.

14. A method as claimed in claim 1, wherein the first path section comprises a metering-in line.

15. A method as claimed in claim 1, wherein pressure data associated with the pressure in the hydraulic fluid supplied to the first side of the actuator comprises at least one pressure pLS of the hydraulic fluid at an outlet of a load sensing directional control valve.

16. A method as claimed in claim 1, wherein the pressure compensating valve is positioned upstream of the load-sensing directional control valve.

17. Apparatus for operating and controlling a hydraulic actuator, the apparatus comprising: a pressure compensating valve and a counterbalance valve; a first path section along which a hydraulic fluid is supplied to a first chamber of the actuator using the pressure compensating valve; a second path section along which the hydraulic fluid is extracted from a second chamber of the actuator using the counterbalance valve; a load-sensing directional control valve wherein the hydraulic fluid is supplied to the first chamber via the load-sensing directional control valve; and at least one device for producing a pilot pressure pPilot in a control fluid based upon obtained data associated with a pressure of the hydraulic fluid supplied to the first chamber of the actuator, wherein both of the pressure compensating valve and the counterbalance valve are configured using the pilot pressure pPilot.

18. Apparatus as claimed in claim 17, further comprising the actuator.

19. Apparatus as claimed in claim 17, wherein said at least one device comprises any one or more of: a determiner; a controller; and a control structure.

20. Apparatus as claimed in claim 17, further comprising a control fluid circuit, or components thereof, for controlling both of the pressure compensating valve and the counterbalance valve.

21. Apparatus as claimed in claim 17 further comprising a computer device configured to receive data associated with a pressure of the hydraulic fluid supplied to the first chamber of the actuator, for determining a pilot pressure pPilot to be generated based upon the obtained data for configuring both of the pressure compensating valve and the counterbalance valve.

22. Apparatus as claimed in claim 17, wherein: the pressure compensating valve is operable for adjusting a pressure of the hydraulic fluid in the first path section; and the counterbalance valve is operable for resisting undesired movement of the actuator.

23. Apparatus as claimed in claim 17, wherein the pressure compensating valve is positioned upstream of the load-sensing directional control valve.

24. A non-transitory machine-readable storage medium encoded with instructions executable by a processor for controlling an actuator using a hydraulic circuit, the hydraulic circuit comprising a first path section along which a hydraulic fluid is supplied to a first chamber of the actuator using a pressure compensating valve, and a second path section along which the hydraulic fluid is extracted from a second chamber of the actuator using a counterbalance valve, hydraulic circuit further comprising a load-sensing directional control valve, the hydraulic fluid being supplied to the first chamber via the load-sensing directional control valve, the machine-readable storage medium comprising: instructions to receive data associated with a pressure of the hydraulic fluid supplied to the first chamber of the actuator; instructions to determine a pilot pressure pPilot in a control fluid based upon the received data; instructions to configure both of the pressure compensating valve and the counterbalance valve using the pilot pressure pPilot.

25. Non-transitory machine-readable storage medium as claimed in claim 24, wherein: the pressure compensating valve is operable for adjusting a pressure of the hydraulic fluid in the first path section; and the counterbalance valve is operable for resisting undesired movement of the actuator.

26. A method of controlling an actuator during operation using a hydraulic circuit comprising a first path section along which a hydraulic fluid is supplied to a first chamber of the actuator using a pressure compensating valve, and a second path section along which the hydraulic fluid is extracted from a second chamber of the actuator using a counterbalance valve, the hydraulic circuit further comprising a load-sensing directional control valve, the hydraulic fluid being supplied to the first chamber via the load-sensing directional control valve, the method comprising the steps of: (a) computing a set pressure pSet in a control fluid in dependence upon a pressure of the hydraulic fluid supplied to the first chamber of the actuator; and (b) configuring both of the pressure compensating valve and the counterbalance valve based on the computed set pressure.

27. A method as claimed in claim 26, wherein: the pressure compensating valve is operable for adjusting a pressure of the hydraulic fluid in the first path section; and the counterbalance valve is operable for resisting undesired movement of the actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There will now be described, by way of example only, exemplary embodiments of the invention with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagram of prior art apparatus for controlling an actuator;

(3) FIG. 2 is a diagram of the prior art apparatus for controlling the actuator of FIG. 1 showing additional structure;

(4) FIG. 3 is a diagram of apparatus for controlling an actuator according to an embodiment of the invention;

(5) FIG. 4 is a representation of a control structure in the apparatus of FIG. 3;

(6) FIG. 5 is a representation of a computer device for implementing the control structure of FIG. 4;

(7) FIG. 6 is a graph of pressure curve results from the apparatus of FIG. 3 in use;

(8) FIG. 7 is a diagram of apparatus for controlling an actuator according to another embodiment of the invention;

(9) FIG. 8 is a diagram of apparatus for controlling an actuator according to a further embodiment;

(10) FIG. 9 is a diagram of apparatus for controlling an actuator according to yet a further embodiment;

(11) FIG. 10 is a diagram of apparatus for controlling an actuator according to yet a further embodiment;

(12) FIG. 11 is a diagram of apparatus for controlling an actuator in the form of a motor according to an embodiment of the invention; and

(13) FIG. 12 is block diagram of a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS

(14) Reference is made firstly to FIGS. 3 and 4. In FIG. 3, there is shown apparatus 101 having a hydraulic circuit 102 which is used for providing an actuator 103 with hydraulic power for operating and controlling the actuator 103.

(15) The circuit 102 has a pressure compensating valve 110 and a counterbalance valve 111 which are configured using a pilot pressure pPilot which is generated based upon a determined pressure pSet. The pressure pSet is determined using a control structure 150. A pressure pLS is measured using a transducer 120 and is passed to a determiner 151 in the control structure 150 as an input, and the pressure pLS is processed in order to determine the pressure pSet for generating the pilot pressure pPilot. The pressure pLS is processed in the determiner 151 by applying a low-pass filter to the pressure pLS, in order to obtain the set pressure pSet. In this way, the set pressure pSet is obtained in dependence upon the pressure as measured in the line 107 with a high frequency component filtered out. This technique can therefore provide an improved basis for configuring the counterbalance valve 111 and the pressure compensating valve 110. The functionality of the counterbalance valve 111 and pressure compensating valve 110 to control the actuator 103 under external loads may thus be improved as the valves 110, 111 can respond on the basis of the pressure in the metering-in line 107 (since the set pressure pSet is based upon the pressure pLS), whilst the processing performed in the control structure 150 can help to suppress instabilities as may be suffered by the prior art.

(16) FIG. 5 shows a computer device 200 including an In/Out unit 201 through which the inputs and outputs of the control structure 150 are conveyed. The computer device 200 further comprises memory 203 for storing any of: data; computer programs and/or machine readable instructions. For example, a computer program for processing a signal of the pressure pLS may be stored using the memory 203. The computer device 200 also includes a microprocessor 202 that can be used for any of processing data, executing programs and/or performing instructions, for implementing the control structure 150. Preferably, the computer device 200 is in the form of a programmable logic controller. It will be appreciated that the control structure 150 and/or the determiner 151 in order to provide its function in determining the pressure pSet could be provided by other forms of apparatus.

(17) Whilst this example illustrates that the pressure pLS may be subjected to filtering, it will be understood that other operations may be applied in order to determine a suitable pressure pSet for generating the pilot pressure pPilot. Such operations may for example include removing a noise component, performing signal smoothing or averaging, analysing or performing an estimation using the pressure pLS. In doing so, empirical or numerical methods could be used.

(18) The pilot pressure pPilot is communicated through control lines 110a, 111a to the X ports of the valves 110, 111 to configure them accordingly. In order to generate the pilot pressure pPilot, the determiner 150 is used to control a proportional pressure relief valve 130, which is used to adjust the pressure of control fluid in the lines 110a, 111a to correspond with the pressure pSet. A uProp signal is generated based on pSet and is passed to the proportional pressure relief valve 130 to operate it appropriately. The uProp signal is output from the In/Out unit 201 of the computer device 200.

(19) Referring again to FIG. 3, the apparatus 101 includes a control fluid tank 121 and control fluid pump 122 for providing a supply of control fluid through a supply line 122i. A control fluid drain line 123 is provided for draining away control fluid. The proportional pressure relief valve 130 is arranged between the pump 122 and the drain line 123, and is adjustable, e.g. by a movable valve spool to bleed off control fluid to a drain, to control communication of control fluid between the supply line 122i and the drain line 123. Thus, the pressure of control fluid in the supply line 122i (and hence the lines 110a, 111b which the supply line supplies) can be determined by the proportional pressure relief valve 130, so as to achieve the appropriate pilot pressure pPilot.

(20) It can be noted further in FIG. 3 that the apparatus 101 includes a pressure distribution valve 131. When a piston 103p of the actuator 103 is being moved toward the second side 103b (upon application of power fluid into a chamber on a first side 103a of the actuator 103), block 131a of the pressure distribution valve 131 is active and control fluid at the pilot pressure pPilot is communicated through the valve 131 into the line 111a and into the port X of the counterbalance valve 111. In FIG. 3, both a load-sensing directional control valve 109 and the pressure distribution valve 131 are in the neutral configuration (blocks 109c and 131c active), with the actuator 103 stationary. In this neutral configuration, the pressure port X in the counterbalance valve 111 is in communication with the drain line 123, and both the supply of the control fluid via pump 122 and supply of power fluid via pump 105 are disconnected.

(21) When the apparatus 101 is used to move the piston 103p, an input signal uMain is passed to the directional control valve 109 to activate the relevant block 109a and an input signal uDist, based upon the input signal uMain, is sent from the determiner 150 to the pressure distribution valve 131 in order to activate the block 109a so as to communicate the pilot pressure pPilot for configuring the pressure compensating valve 110 and counterbalance valve 111 as described above.

(22) In general, operation is such that a pilot pressure is generated using the determiner 150 on an ongoing basis. The pressure pLS is received and the pressure pSet produced by the determiner as time-series data, and the determiner 150 sends a time-series command signal uProp to the pressure relief valve 130 accordingly. The pilot pressure pPilot generated in the control fluid is thus updated over time, e.g. continuously and/or automatically.

(23) In order to facilitate proper generation of the pilot pressure, the generated pressure pPilot is measured using a pressure transducer 140 and is fed back to the determiner 150 as an input. The measured pilot pressure pPilot and the set pressure pSet are compared for checking agreement between the pressure pPilot actually generated and the determined set pressure pSet. A proportional integral (PI)-control function is used to determine any difference pDelta between the measured pressure pPilot generated in the fluid and the pressure pSet, and applies a gain to the pressure pSet signal if appropriate. The signal uProp is then communicated accordingly, taking into account the gain, to control the pilot pressure pPilot being generated in the fluid via the proportional pressure relief valve 130.

(24) FIG. 6 shows time-series plots of data showing the signal of the measured pressure pLS and that of the resulting set pressure pSet after low pass filtering of the signal of the measured pressure pLS. As can be seen, the set pressure pSet after filtering does not contain the high-frequency fluctuations of the pressure pLS observed by measurement of the fluid. Nevertheless, the computed set pressure pSet includes the longer period variations observed in the pressure pLS, so that appropriate configuration of valves 110, 111 can be made to control the actuator 103.

(25) With reference again to FIG. 3, in further detail, it can be noted that the piston 103p of the actuator 103 is movable within a piston housing 103h under control of the pressure compensating valve 110 and the counterbalance valve 111. The piston 103 is bi-directionally movable by hydraulic power fluid acting in a chamber on the first side 103a of the actuator 103 for moving the piston 103p toward a second side 103b or by hydraulic power fluid acting in a chamber on the second side 103b of the actuator 103 for moving the piston 103p toward the first side 103a. The power fluid is supplied through the circuit 102 to the appropriate chamber. The pump 105 is used for supplying the hydraulic power fluid from a tank 104. The chambers on the first and second sides 103a, 103b operate such that movement of the piston 103p, e.g. toward the second side 103b by the fluid supplied into the chamber at the first side 103a, is resisted by power fluid in the other chamber. Accordingly, with a first body of hydraulic power fluid being supplied into one of the sides 103a, 103b, a second body of hydraulic power fluid is expelled from the chamber on the other of those sides 103a, 103b. The power fluid is led into the relevant chamber of the actuator 103 via line 108 or line 107 as appropriate, facilitated by the load-sensing directional control valve 109. It will be appreciated that the configuration of the directional control valve 109 determines the route for the hydraulic power fluid from the pump 105 to the actuator 103. The load-sensing directional control valve 109 is shown in FIG. 3 in a neutral position, in which no movement of the piston 103p is taking place. However, upon activating the directional control valve 109 toward the left hand side as viewed in the figure such that the block 109a is active whereby ports A and T are connected and ports B and P are connected, power fluid can be directed from the pump 105 into the line 107 and into the first side 103a of the actuator 103, for urging the piston 103p toward the second side 103b. Returning power fluid can then be extracted from the second side 103b of the actuator via the line 108 to the drain line 113 to a drain 106.

(26) The pressure compensating valve 110 is configured to adjust the flow of power fluid from the pump 105 so that a suitable pressure is applied for moving the piston 103p at a certain speed. The counterbalance valve 111 can adjust the flow of returning power fluid from the actuator 103 to control the pressure in the chamber on the second side 103b against which the piston 103p needs to act to maintain the speed (when moving for example toward the second side 103b). In the event of variations in the load, the counterbalance valve 111 can adjust the path for fluid out of the second side 103b in order to maintain the speed of the piston 103p independently of the load, e.g. to maintain a pressure differential between the chambers on the first and second sides 103a, 103b of the actuator. Control of the valves 110, 111 using the pilot pressure generated as described above facilitates correct performance of the counterbalance valve 111 and the pressure compensating valve 110 such that potential instabilities as may arise by operation of the valves in the presence of overrunning or other externally imparted loads can be suppressed or prevented.

(27) It can further be noted that the pressure compensating valve 110 is controlled according to the pressures in control lines 110a, 110b e.g. by positioning a valve spool as determined by the pressure in the control lines 110a, 110b. In this way, the pilot pressure in the control line 110a can control the valve 110 so as to configure the path for power fluid through the valve 110. The control line 110b is connected to the inlet side of the load-sensing directional control valve 109 and senses the pressure of the power fluid being supplied into the directional control valve 109 through supply line 112.

(28) The counterbalance valve 111 is controlled according to the pressures in control lines 111a, 111b, e.g. by positioning a valve spool so as to restrict or permit fluid flow through the valve 111 by an amount determined by the pressure in the control lines 111a, 111b. In this way, the pilot pressure in the control line 111a can control the valve 111 so as to configure the path for power fluid through the valve 111. The control line 111b is connected to the line 108 from the second side 103b of the actuator 103 so as to sense the pressure in the returning power fluid from the second side 103b of the actuator in line 108.

(29) FIG. 3 illustrates a simplified version of the apparatus 101 highlighting key components involved for operating and controlling the actuator moving in the direction toward the second side 103b, e.g. when subjected to an overrunning load. In practice, it is also desired to operate and control the actuator in the direction toward the first side 3a of the actuator 103, e.g. when subjected to an overrunning load. The same functionality is thus implemented by mirroring the configuration of the counterbalance valve 111 and check valve 114 on the other side of the actuator 103, and the full configuration for controlling the actuator movements and overrunning loads in both directions is shown in FIG. 7.

(30) In FIG. 7, the apparatus 101 includes a second counter balance valve 111 operative under control from lines 111b and 111a, and a second check valve 114. These operate in alternation with the counterbalance valve 111 and check valve 114, and resist the movement of the piston 103p toward the first side 103a. The second counterbalance valve 111 and check valve 114 operate to resist the movement when the directional control valve 109 has the block 109b active, whereby the ports A and P are connected and ports B and T are connected. When the block 109a is active however, and ports A and T are connected and ports B and P are connected, the counterbalance valve 111 and check valve 114 operate to resist the movement toward the second side 103b.

(31) The counterbalance valves 111, 111 uses separate control lines 111a, 111a to the respective X ports of the valves 111, 111. In order to supply control fluid on these lines 111a, 111a, the apparatus 101 has a pressure distribution valve in the form of a directional control valve 531, operating under control of the uDist signal (which in turn is linked to the uMain load sensing signal). When the piston 103p of the actuator 103 is being moved toward the second side 103b (upon application of power fluid into the chamber on the first side 103a), block 531b of the valve 531 is active and control fluid at the pilot pressure pPilot is communicated through the valve 531 into the line 111a and into the port X of the counterbalance valve 111. Conversely, when the piston 103p of the actuator 103 is being moved toward the first side 103a (upon application of power fluid into the chamber on the second side 103b), block 531a of the valve 531 is active and control fluid at the pilot pressure pPilot is communicated through the valve 531 into the line 111a and into the port X of the second counterbalance valve 111. The neutral configuration with block 531c active is shown in FIG. 7.

(32) In other variants, other arrangements may be used to generate the pressure pPilot in the control fluid, not necessarily using the proportional pressure relief valve 130 as illustrated in FIGS. 3 and 4.

(33) Turning to FIG. 8, one such variant is depicted, in which the apparatus 601 has a valve arrangement 630 for generating the pilot pressure according using the uProp signal, instead of the pressure relief valve 130. The valve arrangement 630 in this example includes a proportional pressure reducing valve 651 which is used to generate the pilot pressure pPilot. A second valve 652 is provided between the pump 621 and the drain line 623 for bleeding off pressure to the drain line 623 to control the pressure of control fluid at the P port of the pressure reducing valve 651.

(34) In the above-described embodiments, the pilot pressure pPilot which is generated from pSet as determined by the determiner 150 is communicated to both the counterbalance valve 111 and the proportional pressure relief valve 130. It will however be appreciated that the pressure pPilot from the determiner 150 can in other examples be applied to one or the other of the counterbalance valve 111 and the pressure compensating valve 110 (or the counterbalance valve 111 and the pressure compensating valve 110 as the case may be). Such examples are illustrated in FIGS. 9 and 10.

(35) In FIG. 9, the apparatus 701 is configured in the same way as the apparatus 101 of FIG. 3 except in this example the pressure pPilot from the determiner 105 is communicated through the line 710a to the X port of the pressure compensating valve 710 and not to the counterbalance valve 711. The pressure pLS is sensed by transducer 720 and fed to the determiner 150. The control line 711a is connected to the line 707 so that the X port of the counterbalance valve 711 senses the pressure in the fluid being supplied to the first side 703a of the actuator 703.

(36) In FIG. 10, the apparatus 801 is configured in the same way as the apparatus 101 of FIG. 3 except in this example the pressure pPilot from the determiner 105 is communicated through the line 811a to the X port of the counterbalance valve 811 and not to the pressure compensating valve 810. The pressure pLS is sensed by transducer 820 and fed to the determiner 150. The control line 810a is connected to an outlet side of the load-sensing directional control valve 809, which senses the pressure in the power fluid being supplied into the first side of the piston via line 807.

(37) The configurations in FIGS. 9 and 10 represent simpler variants that may be effective while still offering improvements in the controllability of movement instabilities by overrunning loads, due to the pilot pressure pPilot being generated based on a computed set pressure pSet from the determiner 105. The system in FIG. 9 can be particularly advantageous because no artificially generated hydraulic pressure is sent to the counterbalance valve which is considered an important safety component. Therefore, the simpler system with the direct connection (provided by line 711a) may benefit from an easier certification requirement.

(38) It can be noted that the presently described techniques can be applied with actuators of different types. The actuators may be multi-directional in their movement, and may be controlled in respective directions using apparatus as described. For example, as illustrated in FIG. 11, rather than a bi-directional linear translation piston such as the pistons 103, 603, 703, 803, the actuator is in the form of a hydraulic motor 903 whereby a moving component in the form of a shaft 903s is rotated by hydraulic control. Shaft movement under load is controlled by an opposing pressure chamber. Thus, movement of the shaft 903s pressure in the line 907 into a first pressure chamber 903a, is resisted by fluid in a second pressure chamber 903b using the counterbalance valve 911.

(39) In FIG. 12, a method 300 of controlling a hydraulic actuator has the steps S1 to S4, as shown. In steps S1 and S2, pressure data providing a signal of the pressure in the power fluid into the actuator is obtained from transducer measurements, and a set pressure is computed based upon the pressure data, e.g. by filtering the signal. In S3, a pilot pressure is generated, e.g. using a pressure relief valve in a control fluid circuit, using the computed set pressure. In S4, the pilot pressure is produced in the control fluid and is communicated via the fluid to the ports in a counter balance valve and a pressure compensation valve, causing the valves to be set according to the pilot pressure. In this way, the paths for power fluid into and out of the actuator are determined by the valves in dependence on the pilot pressure to control the actuator.

(40) Various modifications and improvements may be made without departing from the scope of the invention claimed below.