US 3618470 A
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NOV. 9, 1971 A MUELLER ETAL 3,618,470
DEVICE FOR SUPERVISING ELECTROHYDRAULIC ACTUATQRS Filed June lo, 197C 4 SheGtS-Sh8et l Fig.1
NOV. 9, 1971 A, MUELLER ETAL DEVICE FOR SUPERVISING ELECTROHYDRAULIC ACTUATORS l1 Sheets-Sheet 2 Filed June lO, 197C N .ma
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Nov. 9, 1971 A. MUELLl-:R ErAL 3,618,470
DEVICE FOR SUPERVISING ELECTROHYDRAULIC ACTUATORS Filed June lO, 1970 4 SheetsShoot 3 Fig.3
In entof: A/ red /l/v//er NOV. 9, 1971 A MUELLER ETAL 3,618,470
DEVICE FOR SUPERVISING ELECTROHYDRAULIC ACTUATORS Filed June l0, 1970 4 Sheets-Sheet 4 United States Patent O GmbH Filed June 10, 1970, Ser. No. 45,155 Claims priority, application Germany, June 25, 1969, P 19 32 066.2 Int. Cl. F15b 11/22 U.S. Cl. 91--411 R 12 Claims ABSTRACT OF THE DISCLOSURE A dual cylinder drive with pistons operating a common output actuator and individual feedback control in follower operation as to an electrical input. Any pressure differential between the cylinders lis used to generate a control operation tending to equalize the pressure for similar relative piston positions. In case of excess pressure difference, the drive is shut down.
The present invention relates to electro hydraulic actuators `and more particularly to plural or multiple actuator drive units operating upon a common output, in response to a common electrical input but independent from each other. Specifically, the invention relates to balancing operation of plural cylinder piston arrangements with common output, each being controlled by an individual servo valve.
Actuator drives for the control of displ-aceable objects in high power aircraft require a high degree of operational accuracy. 'For this, single or plural hydraulic actuator drives are used to operate in parallel upon a common output. The drive systems employed include servo valve controlled cylinder having their respective pistons interconnected to operate upon a common output. Plural or multiple actuators include at least two single action drives having their outputs coupled together to provide common actuation.
The operation of each actuator drive system can be supervised through a simulator and by means of load independent electrical or hydraulic comparator devices. However, all inputs operating upon such an actuator systern cannot be defected completely and simulated. Thus, error recognition and shutdown conditions must be chosen on basis of relatively high threshold and of wide limits before a particular actuator displacement length is recognized as erroneous. Thus, on the average, relatively large actuator imbalances among the several drives have to be tolerated, but the shutdown threshold for each drive remains the same. Moreover, tolerances of the several parts in each of the servo valves, in the mechanical linkage and associated electric circuitry may result in input signal processes so that for the same common input, the several drives operate in different directions, i.e., against each other as to their intended attempt to provide a common actuator output. This, of course, amounts to further deterioration of performance. In case the individual cylinder piston arrangements operate with feedback control, a high gain in the feedback path will not necessarily improve operation without rendering the device unstable.
Another known multiple drive uses a common balance type output beam producing the actuator displacement proper. Any difference in the displacement paths as producedby the individual drives is electrically detected. After shutdown of a defective drive the beam has to remain operatively coupled to the other, still operative drive in a manner so that the latter may still provide the re- 3,618,470 Patented Nov.v 9, 1971 quired actuation displacement. It Was found that this requires considerable engineering effort and expenditure.
Still other plural drive systems are known under the designation triplex servo drivers. For supervision of operation, the respective three load pressures act on a balancing beam operating for correcting errors. The beam becomes unbalanced when one of the loads drops out. Thus, the balance beam must be stabilized in order to remain operational, but in that case it is no longer suitable to balance different loads.
In case of triplex actuators, or of actuators with a still larger number of individual drivers, the supervisory control operates in accordance with the majority principle; the majority of properly operating single drives determines the actuator position, overriding operation of the defective one and the latter is turned olf. However, this kind of supervision and individual shutdown still does not avoid disadvantages as to accuracy and turn off threshold as outlined above.
4It is an object of the present invention to improve operational accuracy of single and plural actuator drive systems with plural drive units and relatively large tolerances of the individual components and elements, whereby errors in the actuator displacement are to be avoided.
-In accordance with the invention, actuator arrangements are improved wherein a common actuator is operated by at least two pistons which are individually position-controlled in separate cylinders. The cylinders are under control of servo valves which, in turn, operate in response to input signals. In case of a relatively small pressure differential between the two cylinders, the servo valve control is operated additionally to eliminate that pressure differential in a feedback loop. In case the pressure diferential is relatively large, the two cylinders are turned o Preferably, an input signal controls piston operation, and particularly the respective piston positions are controlled in separate feedback loops as to each cylinder. The pressure differential control is a feedback control operation that is superimposed upon one cylinder to cause the pressure in that cylinder to be equal to the pressure in the other one. Thus, the invention is based on the principle of equalizing the pressure in the two cylinders of a single actuator drive, causing one piston to track the other one. Damping and integration of the pressure differential as sensed results in a control signal that is superimposed upon the actuator feedback control as rate action for increasing stabilization thereof. In case of plural or multiple actuation drives, they are matched to each other as in case of plural cylinders of a single actuation drive. l
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects land features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:
FIG. 1 illustrates somewhat schematically a dual cylinder single actuator drive;
FIG. 2 illustrates a modification of the device in FIG. 1;
which are arranged in side-by-side relationship. The cylinders receive pistons 1a and 2a respectively which are connected to piston rods 1b and 2b. The respective upper ends of the piston rods are secured to and interconnected 3 by a cross beam or traverse 5, serving as or to which is connected an actuator.
fEach principal cylinder is associated with a servo valve, as schematically indicated by 3a and 3b, which are electrically operated and have inputs derived respectively from two comparators 4a and 4b, pertaining to a comparator network 4. Each of the two comparators 4a and 4b receives the same reference signal from a source 4c to provide follower control. The servo valves 3a and 3b are hydraulically pressurized from a pressure line 131 that is run through a master control valve 13 normally admitting pressure fluid to the two servo valves, but in cases pressure can be turned off by the valve 13.
Piston rods 1b and 2b are respectively connected to the displacement element such as a tap of potentiometers 6 and 7. The taps are particularly disposed on tap actuator rods 6b and 7b and the resistance elements of the potentiometers are denoted 6a and 7a respectively. The output of potentiometer 6 is connected to one input of cornparator 4a; the output of potentiometer 7 is connected to one input of comparator 4b. The potentiometer taps have position in the drawing opposite to the output terminal or the resistance element equivalent of zero output to be taken from the potentiometer and corresponding to a central position of the pistons in the respective cylinders.
The resistive element 6a of potentiometer 6 is an axially displaceable lining or tube in a bore of the principal housing. The lower end of that displaceable tube is connected to a piston rod 8b of a piston 8a that is displaceably disposed in an auxiliary cylinder 8. The two chambers in cylinder t8 as established by control piston 8a therein are respectively connected to the two cylinders 1 and 2 via suitable conduits. Thus, piston 8a is operated as a differential piston responding to any pressure difference in the lower chambers of cylinders 1 and 2.
Each of the two fluid paths as leading to differential piston chamber 8 includes a hydraulic choke, throttling or damping member 9. The lower end of piston rod 8b is connected to a stabilizing spring 10. Additionally, piston rod 8b carries a cam member 20 for operating an electric switch 1,1 via a suitable feeler which rides on the cam surface of member 20. Switch |11 operates valve 13 in dependence upon the pressure differential in cylinders 1 and 2. In the illustrated, medium position of differential piston 8a and of cam 20, switch 11 is operated to maintain valve 13 in the open position. In either the upper or lower limit position of the cam, switch 11 controls closing of valve 13.
The resistance element of potentiometer 7 is fixed, but it has, of course, a movable tap element connected to rod 7b as linked to piston rod 2b. The device as outlined above operates as follows:
Pressure uid is fed to the two cylinders 1 and 2 as normally valve 13 is open. However, servo valves 3a and 3b are normally closed, thus blocking the fiuid path to the cylinders. A particular pressure prevails in the cylinders and maintains the pistons in a particular position. For example, the pistons are illustrated in a medium position that may correspond to a neutral position on the actuator. Also, the reference signal for these positions may be zero, and the feedback signals for each comparator 4a and 4b may likewise be zero.
As a non zero reference signal is passed from source 4c to the two comparators 4a and 4b, the resulting output signals thereof open the servo valves 3a and 3b in a particular direction depending upon the sign of the output of the comparators 4a and 4b. Thus, servo valves 3a and 3b connect respectively one or the other passage each for cylinders 1 and 2 to pressure line 131, and the respective other passages may be opened for venting. Accordingly, pistons 1a and 2a are moved up or down as required. These piston movements are, up to this point, independent from each other; they depend solely on the sign of the outputs of the comparators and are individually controlled by the servo valves.
The resulting displacement of piston rods 1b and 2b provides common actuating displacement upon traverse 5. The individual piston rod displacements are directly but individually transmitted upon the movable adjusting element 6b and 7b of the two potentiometers. It can, thus, be seen that the electrical signals as derivable from the two potentiometers, are proportionally dependent upon the actual position of the respective pistons (1a, 2a). These electrical signals are fed to the tWo cornparators, and as the pistons change position, these signals change proportionately thereto.
The two comparators, thus, provide a comparison between a reference value (source 4c) and signals representing piston positions. Each servo valve remains open until the respective comparator inputs balance, whereupon the respective servo valve closes. Ideally, both pistons 1a and 1b should move in unison during the displacement operation, i.e., they should have similar speed and move through similar positions in the respective cylinders at the same rate. In this case, each position provides the same displacement upon traverse 5 and upon the common actuator and object to be actuated. However, it has to be observed that tolerances or some unbalance in the control may result in dissimilar positions for the pistons 11a and 2a, even though the two comparators furnish similar outputs. Accordingly, the two cylinders have different pressures during displacement action resulting in differing piston positions, which difference may persist even by time of termination of valve operation, when both cornparators have zero output. The auxiliary equipment to be described next avoids this possibility.
The particular auxiliary equipment provided to offset the above mentioned imbalance, is comprised of the auX- iliary cylinder-piston arrangement 8-8a controlling the normally stationary resistance member 6a of potentiometer 6 in response to a pressure differential in chambers 1 and 2. As the pressure differential actuates piston 8a, the resistance element 6a of potentiometer 6 moves relative to the potentiometer tap on rod 6b. As a consequence, comparator 4a receives an input signal wherein the piston position indicating signal is modified by signal representating the measured pressure differential. Thus, servo valve 3b controls displacement of piston 2a strictly in proportion to the input signal from source 4c. Servo valve 3a controls basically displacement of piston 1a in an analogous manner, but subject to an additional pressure equilization control, matching the pressure in cylinder 1 to that in cylinder 2 in representation of similar actual positions.
The motion of auxiliary piston 8a is damped due to chokes 9 and spring 10 stabilizes the position of the pressure differential sensing means Saz-8b. This vvay, the auxiliary equipment causes the feedback loop for cylinder 1 to track operation of the loop for cylinder 2 so that the auxiliary equipment does, in fact, operate as a fine-adjuster. In case the pressure differential between the cylinders is rather high, cam 20 is displaced to such an extent that the feeler actuates switch 11 which, in turn, causes valve 13 to close off the pressure supply.
The single actuator drive of FIG. 2 has hydraulic operating equipment as described including the pressure differential sensing piston 8a. However, the two potentiometers 6 and 7 are constructed similarly, each having but one adjustable component, the tap on the respective rod 6b and 7b. The differential pressure sensing piston has its piston rod connected to the resistance portion of another potentiometer 12, the glider thereof provides a third input for comparator 4a. The comparator input circuit superimposes the output of potentiometer 12 upon the output of potentiometer 6 so that the combined signal is similar to that derived from displaceable potentiometer 6 in FIG. 1. Thus, the devices in FIGS. 1 and 2 have similar operation, but the double displacement of potentiometer 6 in FIG. 1 is avoided in FIG. 2.
The particular drive system of FIG. 3 is constructed differently in that the two pistons 1a and 2a act along the same axis and are mounted to a common piston rod a. That particular kind of arrangement will be chosen primarily for reasons of availability and contour of mounting and installation space, particularly where construction in accordance with the layout of FIGS. l and` 2 would pose difficulties. The control and balancing operations as to the position establishing pressure for pistons 1a and 2a are the same as in IFIG. 2, but could be modified to follow the design principles of FIG. l as to establishing pressure balancing control. It can thus be seen that the dual feedback system, one for each of the on-line operating pistons, in conjunction with the pressure balancing control establishes balanced equilibrium in the actuation system as a whole.
Turning now to FIG. 4, there is illustrated an example for a plural actuation drive, particularly two twin piston drives, I and II, are shown working on a common traverse 5b. The twin piston drive II is similar to the one shown in FIG. l, but the embodiment of FIG. 2 could be chosen. Drive II has many components similar to drive I, the components are identified by a In drive II, the resistance element 7'a is presumed to be displaceable in response to pressure differential in the piston chambers 1 and 2. A differential piston v14a in auxiliary piston chamber 14 monitors that pressure differential.
Thus, each twin cylinder drive has its own pressure balancing and control device, operating as aforedescribed, whereby, however, the source of reference signals 4c is common to all drives so that the same reference signal is used in both of the comparing circuits 4 and 4. Most particularly, each drive can be shut down independently, as each has its own excess differential pressure switch 1'1 and 11', respectively, for the two independently operating turn-off valves 13 and 13'.
In addition, the two drives are regulated in mutual dependency. For this, for example, there is provided the pressuer differential sensing chamber 8 with a sensing piston Sa. One side of that chamber connects to cylinder 2 of drive I, the other side of that sensing chamber connects to cylinder 1' of drive II. Thus, this coupling control affects piston 1a and the control for twin drive II balances to the operational state of drive I.
The coupler control for drives I and II, particularly piston rod 8b thereof, is also spring biased but not constructed as cam actuator for operating a switch. The two switches 11 and 11' merely respond to excess pressure differential in the cylinders of each twin drive, while no such supervisory function is needed as between the relative adjustment of drives I and lII to each other.
Assuming that during operation a pressure imbalance occurs, one can see that piston 2a in cylinder 2 serves as master and its feedback loop is the leader. Any pressure differential relative to cylinder 1 is sensed by differential piston 8a in that comparator 4a is controlled for piston 1a to track piston 2a. Likewise, displacement control for piston 1 is forced to follow piston 2a, and piston Z'a in turn is forced to follow piston '1'a. Should an excess pressure differential occur in drive II, that drive is disconnected and actuation is carried on by drive I alone. Any pressure differential between cylinders 2 and 1 is disregarded. In case an excess pressure differential occurs in drive I, the drive` is shut down and the pressure differential sensing piston 8a moves into a terminal position or there may be provided stop means arresting the position of piston 8a (and particularly of resistance 6a) in a medium position, so that for further operation that potentiometer has a particular stationary position.
It should be mentioned that the pressure differential of the respective two cylinders in a twin drive system is shown as being measured by a differential piston. Instead, a perssure transducer could be used from which an electrical signal can be derived directly to be used as shown 2as third input for vvone of the comparators.
. 1. In an actuator arrangement wherein a plurality of pistons operate on a common output in response to a common electrical control input signal, the pistons of the plurality respectively disposed in cylinders which are pressure controlled through servo valve means, there being a source of pressurized fluid for connection to the cylinders via the servo valve means, the combination comprising:
control means connected to be responsive to the control signals to control individually the servo valve means, to obtain position adjustment of the pistons of `the plurality;
means responsive to the pressure differential in two of the cylinders of the plurality connected to operate the control means in response to the pressure differential to control the servo valve means to obtain pressure equalization in the two cylinders; and
threshold means disconnecting the two cylinders from the source of pressure if the pressure differential exceeds a predetermined limit.
2. In an actuator arrangement as in claim 1, there being a servo valve associated with each cylinder, a potentiometer associated with each cylinder and having an adjustable element connected to the respective piston, to provide a signal representative of the position of the piston in the cylinder, comparator means included in the control means and connected to be responsive to the control signals and to the piston position signals to control the respective servo valves, whereupon the piston position signals tend to equalize with the first control signal and further connected to operate the comparator means for control of equali'zing the pressure in the two cylinders.
3. In yan actuator arrangement as in claim 2 there being a particular potentiometer associated with one of the two cylinders, and having first and second parts movable independently from and relative to each other for potentiometer adjustment, the first part connected to the piston in the cylinder, being displaced therewith, the second part operated in response to the pressure differential.
4. In an actuator arrangement as in claim 3, there being an auxiliary cylinder coupled to the two cylinders, and a piston disposed in the auxiliary cylinder, operated as differential piston and connected to the second part of the potentiometer for controlling the position thereof.
5. In an actuator arrangement as in claim 4, the first part being the moveable tap, the second part being the resistance body of the potentiometer.
6. In an actuator arrangement as in claim 1, including an auxiliary ,cylinder coupled to the two cylinders and having a piston operated as differential piston in response to the pressure in the two cylinders, the differential piston coupled to the control means to obtain pressure equalization in the two cylinders.
7. In an actuator arrangement as in claim 6, there being a potentiometer coupled to the differential piston to provide an electrical signal representative of the pressure differential, the latter electrical signal processed in the control means to obtain pressure equalization.
8. In .an actuator arrangement as in claim 6|, the differential piston being position-stabilized by means of a spring.
9. In an actuator varrangement as in claim 6, the differential piston coupled to a cam operated switch means that is actuated in response to excessive pressure differentia 10. In an -actuator arrangement as in claim 1, the pressure differential means being a transducer providing an electrical signal indicative of the pressure differential.
11. In an actuator arrangement as in claim 1, the control means including a first one of the servo 'valves to establish a first feedback loop for position control of a first one of the two pistons and in follow-up configuration as to the control input, the control means further including a second one of the servo valves to establish a second feedback loop for position control of a second one of the two pistons, also in follow-up configuration as to the control input, the means responsive to the pressure control operating the control means to control pressure in the respectively associated irst cylinder for tracking the pressure in the respective second cylinder, thereby modifying the position control for the first cylinder.
12. In an actuator arrangement as in claim 11, there being a third cylinder and piston arrangement the piston coupled to the common output, there being means to ascertain the difference in pressure between the third and the second cylinder and to control pressure in one of the third and second cylinders in response to said difference.
8 References Cited UNITED STATES PATENTS 3,411,410 11/1968 Westbury et al. 91--411 R XR 3,505,929 l4/1970 Coppola et al. 91-411 R XR 3,426,650 2/1969 Jenney 91-363 A XR EDGAR W. GEOGHEGAN, Primary Examiner U.S. Cl. X.R.