US3096497A

US3096497A - Combination hydraulic actuator and potentiometer

Info

Publication number: US3096497A
Application number: US93410A
Authority: US
Inventors: Donald F Sellers
Original assignee: Ling Temco Vought Inc
Current assignee: Ling Temco Vought Inc
Priority date: 1961-03-06
Filing date: 1961-03-06
Publication date: 1963-07-02
Anticipated expiration: 1980-07-02

Description

D. F. SELLERS 3,096,497

COMBINATION HYDRAULIC ACTUATOR AND POTENTIOMETER July 2, 1963 Filed March 6, 1961 FIG 2 FIG .3

FIG 4 BIA // 7///////////////////II////IIII////IA 'II/II.

INVENTOR.

DONALD E SELLERS AGENT 3,096,497 COMBINATIGN HYDRAULIC ACTUATOR AND POTENTIOMETER Donald F. Sellers, Dallas, Tex., assignor, by mesne assignments, to Ling-Temco-Vought, Inc., Dallas, Tex., a corporation of Delaware Filed Mar. 6, 1.961, Ser. No. 93,410 Claims. (Cl. 338-83) This invention relates to hydraulic actuators and more especially to a combination hydraulic actuator and potentiometer.

Wherever hydraulic actuators are employed, it is frequently necessary that an electrical device be employed in conjunction therewith for providing an electrical signal indicative of the position of the actuator piston and hence of the item, for example, an aircraft aileron or other control surface, moved by force exerted by the actuator. The electrical signal thus obtained may be utilized for operation of an instrument giving visual or other indication of the position of the actuator movable element within its range of travel; and an electrical signal of this kind is indispensable for operation of an electrical system for servo control of the actuator. To obtain the electrical signal, it has been customary to provide a potentiometer for operation with the hydraulic actuator and to connect the potentiometer movable element, through a suitable linkage, with a movable element (usually the piston rod) of the actuator. While such arrangements have made possible a relatively excellent versatility and precision of servo control of hydraulic actuators, they have had certain serious disad vantages. Refinement of design and various expedients relating to the mounting and use of these potentiometers have been carried as far as possible in an effort to minimize the problems occasioned by these disadvantages, and while much inventive skill and craftsmanship have been expended, such problems have only been somewhat alleviated thereby and never altogether satisfactorily solved.

Potentiometers for applications such as mentioned above tend to be relatively expensive in themselves, and their mounting means and especially the often quite complicated and close-tolerance linkage utilized for their connection to an actuator movable element also add much expense. Potentiometers generally tend to be relatively delicate of construction, and unless especially protected are readily injured by chance blows and by mechanical shocks transmitted to them through the actuator or other structure on which they are mounted. Upon installation of the potentiometer, it and/ or its linkage must be rigged and adjusted for accurate operation in response to movement of the actuator, and this task is exacting and timeconsuming. Inaccurate rigging or the effects of vibration, shock, etc. which distort or injure the potentiometer linkage or throw it out of adjustment can result in improper operation of the actuator by the servo control system with results that, in many applications, can be very seriously destructive. To alleviate the dangers of mechanical injuries, many potentiometers have been mounted inside the associated actuator; quite effective in protecting the potentiometer, this expedient at the same time results in greatly increased complexity in design, fabrication, assembly and maintenance of the actuator and potentiometer.

While it is highly desirable to solve the above and other problems which arise where a potentiometer is employed in association with a hydraulic actuator, the more general need exists for a more rugged, simply constructed, and reliable potentiometer for use in still other applications whether or not requiring the operation of a hydraulic actuator,

ice

Accordingly, it is a major object of the present invention to provide a potentiometer which is sturdy and reliable and not subject to injury from blows and mechanical shocks.

Another object is to provide a potentiometer of simple construction and requiring no special protection.

A further object is to provide a device usable as a potentiometer and connectable into a hydraulic system for use either as a hydraulic actuator or as both an actuator and potentiometer.

Yet another object is to provide a combination actuator and potentiometer which dispenses with linkages between an actuator and potentiometer and which is not subject to malfunction or failure because of improper adjustment of or damage to such a linkage.

Still another object is to greatly simplify and add to the reliability of a hydraulic system employing a servocontrolled actuator by providing an actuator which simultaneously serves as a potentiometer and whose construction is of superior simplicity and sturdiness.

Still other objects and advantages will be apparent from the specification and claims and from the accompanying drawing illustrative of the invention.

In the drawing,

FIGURE 1 is a View, in longitudinal section, of a potentiometer according to the present invention;

FIGURE 2 is a fragmentary view of the potentiometer employing a shunt resistance;

FIGURE 3 is similar to FIGURE 2 but employing an arrangement without the shunt resistance; and

FIGURE 4 is a view, partially schematic showing the potentiometer in longitudinal section and connected into a hydraulic system for operation as a combination potentiometer and hydraulic actuator.

The linear potentiometer shown in FIGURE 1 includes a vessel or barrel assembly 10 whose cylinder 11 is provided with a pair of

caps

12, 13, one on each of its ends. The inner surface 14 of the vessel 10, i.e., the combined inner surfaces of the cylinder 11 and

end caps

12, 13 closing off the ends of the cylinder, is non-conductive except in local areas in the region of each end of the vessel. Thus, the cylinder 11 conveniently is made of a dielectric material such as a plastic, while the

end caps

12, 13 are made of a conductive material such as a metal to provide each with a conductivesurface exposed to the interior of the cylinder. According to a preferred construction, the

end caps

12, 13 are of a dielectric material similar to that of the cylinder 11 and each has bonded or otherwise attached to its inner face a plate of metal or other conductor. The plates thus provide a first conductive portion 15 of the vessel inner surface 14 which is located in the region of one end cap 12 and a second, similar portion 16 in the region of the other cap 13. The balance of the inner surface 14 is non-conductive; therefore, it physically and electrically separates and isolates the two

conductive portions

15, 16 from each other. Of fixed location relative to the vessel 10, the

conductive portions

15, 16 shortly will be seen to provide the two outer ends or terminals of a pair of resistance elements.

A piston 17 slidably mounted in the cylinder 11 between the two conductive portions :15, 16 of the vessel inner surface 14 is provided with suitable sealing means 18 as required for effecting a good sealing off of the cylinder interior at one side of the piston from that at the other. The piston 17 thus sealingly divides the cylinder interior into two variable-volume chambers. It is essential that the two faces 19, 20 of the piston 17 be conductive and electrically joined or connected together. This is readily effected by making the piston of metal or, as shown, of a material similar to that of the cylinder 11 and providing on it a pair of metal faces 19, joined by a conductor or conductors such as the flush rivets 21.

A rod 22 is rigidly attached at its inner end to one side of the piston 17 and extends out of the vessel 10 through an opening in one of the end caps, suitable sealing means 24 being provided at the opening to prevent leakage. The rod, preferably made of a dielectric material, has an internal passage 25 which extends axially of the rod, from a point always outside the vessel =10, to the piston 17. Also made of a dielectric material, a second rod 23' is attached to the other side of the piston 17, extends out of the vessel through a suitably sealed opening in the other end cap 13, and is of the same diameter as the first rod 22.

Both chambers are filled, preferably completely, with a conductive liquid 26 which extends, in each chamber, from a

respective end cap

12 or 13 to the most nearly

adjacent face

19 or 20 of the piston 17. Thus, in each chamber, the liquid forms a

resistance element

27 or 28 whose length is variable by movement of the piston and whose outer-end terminal is an end cap and whose innerend terminal is a face of the piston. Physically isolated from each other by the piston 17, the two

resistance elements

27, 28 are electrically connected by the piston faces 19, 20. As employed herein, the term conductive, which term is always a relative one,-refers to a degree of conductivity which is high compared to that of a conventional hydraulic oil, the latter generally being an insulator. On the other hand, the term conductive does not include herein a conductivity such as that of a storage battery electrolyte, whose lack of resistance would defeat the purpose of the invention. The term is employed with reference to a liquid whose conductivity is of suitable value for providing, from end to end of the serially connected

resistance elements

27, 28, a resistance comparable to that which would be employed, in a given application, in a wire-wound or other conventional potentiometer. To provide a simple and readily obtainable example of such a liquid, the cylinder is described as filled with Water containing only the amount of a salt or other ionizing material required for providing the desired degree of conductivity. Other liquids will immediately suggest themselves: for example, a conventional hydraulic oil to which has been added enough finely divided carbon or other conductive additive to provide a desired degree of con ductivity.

Since the

piston rods

22, 23 are the same size, a given motion of the piston 1'7 reduces the volume of one chamber of the vessel 10 by the same amount that it increases the other. To permit the motion of the piston 17 and maintain both chambers of the vessel 10 full, means must be provided for allowing the escape of a given quantity of the liquid from one chamber with concurrent admission, during motion of the piston 17, of an equal quantity of liquid into the other. The barrel assembly 10 has two ports 29, 30, one in the region of each of its ends. A tube end 31 connects into the port 29 and a tube end 32 into the port 30.

A shunt resistance will frequently be required across the potentiometer, and in other cases such a resistance, though not actually required, may be present Without interfering with the intended operation of the potentiometer. In both such cases, the

tube ends

31, 32 are part of a single tubular structure (FIG. 2) whose inner surface defines a passage leading out of the vessel 10 in the region of one end cap 12 and back into the vessel in the region of the other end cap 13. The tubular structure 33 preferably is of a non-conductive material in order that the additional, conductive liquid 34 with which it is filled will constitute the sole electrical connection between the two ends of the vessel 10 and form a shunt resistance. The same result is obtainable by making the tube 33 of a conductive material and providing it with a non-conductive inner coating or layer, and the same applies to the vessel 10, which may be of conductive material whose inner surface is lined with an insulating material. The value of the shunt resistance 34 is controllable to a desired value by varying the length and diameter of the tube 33. Where as high a shunt resistance value as possible is desired, the tube 33 is made as long and of as small a diameter as possible without making physical resistance to liquid flow, between the ports 29, 39, so high as to unduly slow the rate at which the piston 17 can be moved by a normally utilized force applied to one of its

rods

22, 23. For a lower resistance, the tube 33 is shortened and/or made of greater diameter; or a medial portion of the tube is made of a conductive material.

Where no shunt resistance at all is desired, the tube ends 31, 32 are not interconnected as in FIG. 2 but instead are individually connected into respective receptacles such as hydraulic accumulators 35A, 3513 (FIG. 3). In this configuration, the materials and/or mounting of the

tubes

31, 32 and

accumulators

35A, 35B are such that there is no electrical continuity between the liquid in one

accumulator

35A or 35B and that in the other.

The potentiometer further requires means for effecting electrical connection to the conductive portions 15', 16 of the vessel inner surface 14 and to the piston faces 19, 2%). A device such as the conductor stud 36 (FIGURE 1) extends through the end cap 12 from the conductive portion 15, and a similar stud 37 is provided at the other end cap 13. A battery 38 or other means for placing an electrical potential between the

conductive surfaces

15, 16 is connected to the

studs

36, 37 as by the pair of

leads

39, 40. For connection of the potentiometer wiper or piston 17 to a position-indicating instrument, a servo control system, etc. a conductor such as a Wire 41 extends into the outer end of the passage 25 in the piston rod 22 and through the passage 25 to the piston 17, with both

faces

19, 20 of which it is electrically connected. The dielectric rod 22 electrically isolates the conductor 41 from the surface conductive portion 15 through which it passes and also from the conductive liquid 26.

One or both the

rods

22, 23 is provided with a rod end 42. When the rod end 42 is connected to a body subject to changes in position, the piston 17 is moved in one direction or the other by movement of the body and always has a position in the cylinder 10 which is in accordance With the position of the body. With the piston 17 centrally positioned in the vessel 10', the conductor 41 provides a signal Whose polarity is midway between that of the two

conductive portions

15, 16; as the piston 17 is moved away from center, the polarity of the signal changes in accordance with that of the

conductive portion

15 or 16 toward which movement is made by the piston 17 and with the size of the intervals separating the piston 17 and the respective

conductive portions

15, 16. Since both

rods

22, 23 are of equal diameter, the crosssectional area of each

resistance element

27, 28 is the same, as is the resistance per given unit of length of the elements. Consequently, voltage change at the conductor 41 in response to movement of the piston 17 tends to be linear.

It will be noted that there is no sliding of a movable Wiper element along a resistance wiper or equivalent. Whereas conventional otentiometers have a fixed resistance element along which a movable element or wiper slides, the present device employs a pair of

resistance elements

27, 28 with fixed outer ends (defined by the conductive portions 15, 16) and connected in series at their inner ends by the movable element or piston 17. Physically separated from each other by the piston 17, the

resistance elements

15, 16 change their respective lengths in accordance with motion of the piston 17. Thus, the only sliding contacts are between the piston 17 and cylinder 11 and the

rods

22, 23 and

end caps

12, 13. Since these elements readily lend themselves to a strong and rugged construction, very little wear on them results, and there is no wear at all between the

liquid resistance elements

27, 28 and potentiometer wiper (piston faces 19, 20). The device, because of its simple, sturdy construction, is well able to withstand blows, vibration, and shocks which would prove injurious to other potentiometers; it needs no special protection of the kind which must be given the more delicate, conventional potentiometers. Because of this simplicity and sturdiness, the potentiometer is of high reliability. The voltage output of the potentiometer is continuously variable with wiper position and is not subject to the resolution deficiencies of wire-wound potenti-onieters. While thus of excellent usefulness as a potentiometer, the device, as will now be explained and described, is connectable into a hydraulic system for operation as both an actuator and potentiometer.

The vessel A of FIGURE 4 is similar to that already described in connection with FIGURE 1, or (as shown) it may employ metal end caps 12A, 13A. The piston 17A also is of metal; thus, the piston faces 19A, 29A as well as the end cap

inner surfaces

15A, 16A are conductive. Where a linear potentiometer is desired, two equaldiameter piston rods may be employed as in FIGURE 1. Where a non-linear operation is required, one of the two rods is of smaller diameter than the other, or (as shown) one is omitted altogether. The device is used in conjunction with a hydraulic system comprising a reservoir 43 containing the same conductive liquid 26 that fills the barrel assembly and which supplies the liquid to a pump 44. The latter has a port or outlet 45 to which it supplies the liquid 26 under pressure.

Connecting means for conducting the liquid 26 comprise

hydraulic lines

46, 47 connected between the barrel assembly ports 29A, 30A and the reservoir 43 and pump 44. Depending on the desired mode of operation of the vessel 10A and piston 17A as a hydraulic actuator, a valve 48 is interposed in one or both of the

lines

46, 47 from the pump 44 and reservoir 43 to control the admission of the conductive fluid 26 to the vessel 10A. As a typical example, the four-way valve 48 connects the pressure line 47 from the pump 44 to the tube 32A leading to the port 30A at the right-hand end of the vessel and the return line 46 to the tube 31A leading to the other port 29A; or the valve setting is changed to reverse these connections as desired. To prevent a direct short across the potentiometer, a resistance must be introduced between these ports 29A, 30A. For this purpose, at least one of the

tubes

31A, 32A leading into the ports 29A, 30A is made of a non-conductive material, thus providing, in the connecting means, a segment, for example the tube 31A, within the length of which only the liquid 26 is conductive. Of the conductive liquid 26 additional to that in the vessel, the additional liquid being contained in the

hydraulic lines

46, 47 with

subjoined tubes

31A, 32A and in the reservoir 43 and pump 44, it is the liquid within the non-conductive tube 31A (or

tubes

31A, 32A) connected to the ports 29A, 30A which provides and establishes the shunt resistance value between the ports.

Leads 39A, 40A and a conductor 41A strung through the piston rod 22A are employed as before to effect electrical connection to the

conductive portions

15A, 16A of the barrel assembly inner surface 14A and to the piston faces 19A, A.

Upon the conductive hydraulic liquid 26 being supplied by the pump 44 to one of the ports 29A or 30A, the resulting motion of the piston 17A forces an equivalent amount of liquid out the other port 29A or 36A and into the return line 46. A body (for example, an aircraft control surface) connected to the piston rod end 42A is moved by displacement of the piston 17A. The voltage on the conductor 41A varies, as already explained, with the position of the piston 17A relative to the

conductor portions

15A, 16A. Thus, the device operates as a combination hydraulic actuator and potentiometer. All linkages formerly necessary between a hydraulic actuator and a potentiometer are eliminated, as is all likelihood of malfunction or failure because of improper adjustment of or damage to such a linkage. Much simplification also is efiectedand reliability is increased by eliminating the linkage and also by obviating the necessity for mounting and protecting a separate potentiometer. Since, in the particular example shown in FIG- URE 4, one resistance element 27A has its cross-sectional area reduced by the presence of a piston rod 22A while the other element 28A does not, the rate of change in resistance value accompanying movement of the piston 17A through a given distance is greater in the resistance element 27A than in the other. As a consequence, the action of the potentiometer, as to the voltage supplied by the piston 17A to the conductor 41A, is non-linear; and the extent of the non-linearity may be increased or decreased as desired by increasing or decreasing the diameter of the rod 22A or eliminated altogether by providing tw-o equal-diameter rods as in FIGURE 1.

While only one embodiment of the invention, together with modifications thereof, has been described in detail herein and shown in the accompanying drawing, it will be evident that various further modifications are possible in the arrangement and construction of its components without departing from the scope of the invention.

I claim:

1. A potentiometer comprising: a vessel having an inner surface and including a cylinder and a pair of end caps closing off the ends of the cylinder; a portion of said inner surface in the region of one and a portion of said inner surface in the region of the other of the end caps, said portions being conductive and the balance of the inner surface being non-conductive and electrically isolating the conductive portions from each other; means for effecting electrical connection to each conductive portion; a piston slid-ably mounted in the cylinder and dividing the vessel into two chambers, the piston having conductive, electrically connected faces; a conductive liquid filling both chambers, the liquid in one chamber being electrically connected to the liquid in the other by the piston faces and the conductive faces being electrically connected through the liquid in the chambers and the piston faces; a conductor connected to the piston faces and electrically isolated from the liquid and the conductive surfaces, said conductor having an end extending outside the vessel; and material having a non-conductive inner surface defining a passage leading out of the cylinder in the region of one of the end caps and back into the cylinder in the region of the other of the end caps, the passage being filled with the conductive liquid.

2. A linear potentiometer comprising: a vessel having an inner surface and including -a cylinder and a pair of end caps instrumental in closing off the cylinder ends, each end cap having an opening therethrough; a portion of said inner surface in the region of one and a portion of said inner surface in the region of the other of the end caps, said portions being conductive and the balance of the inner surface being non-conductive and electrically isolating the conductive portions from each other; means for effecting electrical connection to each conductive portion; a piston slidably mounted in the cylinder and dividing the vessel into two chambers, the piston having conductive, electrically connected faces; a first dielectric rod of given cross-sectional area connected to one side of the piston and extending out of the vessel through the opening in one of the end caps; a second dielectric rod of the same cross-sectional area as the first connected to the piston and extending out of the vessel through the opening in the other end cap; a conductive liquid filling both chambers, the liquid in one chamber being electrically connected to the liquid in the other by the piston faces and the conductive surfaces being electrically connected through the liquid in the chambers and the piston faces; a conductor connected to the piston faces and electrically isolated from the liquid and the conductive surfaces, said conductor having an end extending outside the vessel; and means keeping the vessel full of the conductive liquid upon sliding of the piston in the vessel.

3. A potentiometer comprising: a vessel having an inner surface and comprising a cylinder with closed ends; a first, conductive portion of said inner surface in the region of one and a second, conductive portion of said inner surface in the region of the other of the ends of the vessel and exposed to the interior of the vessel in fixed location relative to the same; a piston with electrically joined, conductive faces mounted in the cylinder and dividing the same into first and second chambers; first and second resistance elements physically isolated from each other and electrically connected by the piston, each of said elements including a conductive liquid filling a respective one of said chambers and extending between a respective one of the conductive surfaces and the piston; an electrical shunt resistance across said elements and including conductive liquid contained in a passage having one end opening into one of the chambers and another end opening into the other of the chambers adjacent the cylinder ends.

4. A combination hydraulic actuator and potentiometer comprising: a barrel assembly having two end caps and an inner surface; a first conductive portion of said inner surface in the region of one and a second conductive portion of said inner surface in the region of the other of the end caps; a non-conductive portion of the inner sur face extending between and electrically isolating said conductive portions from each other; a piston s-lidably mounted in the barrel assembly between the conductive portions and sealingly dividing the barrel assembly into two chambers, the piston having conductive, electrically connected faces; :a dielectric rod connected to the piston and extending outside the barrel assembly through one of the end caps, the rod having an internal, axially disposed passage extending from the region of the piston to a point outside the barrel assembly; a conductor connected to the piston faces and extending outside the barrel assembly through the passage of the rod; a conductive liquid filling both chambers of the barrel; a port in each end of the barrel assembly whereby conductive liquid may be forced into and discharged from the barrel assembly for effecting movement of the piston and rod; and means for effecting electrical connection to each conductive portion for placing an electrical potential between them.

5. In combination, a reservoir; a conductive liquid contained by the reservoir; a pump having an outlet and receivingly connected to the reservoir for sup plying the conductive liquid, under pressure, at the outlet; a vessel having an inner surface and comprising a cylinder with closed ends; a first conductive portion of said inner surface in the region of one and a second conductive portion of said inner surface in the region of the other of the ends of the vessel and exposed to the interior of the vessel in fixed location relative to the same; a pair of electrical connecting means, one means being connected to the first and the other means to the second of said conductive surfaces; means placing an electrical potential between said electrical connecting means; a piston with electrically joined, conductive faces mounted in the cylinder and sealing-1y dividing the same into first and second chambers; a conductor connected to the piston faces and having an end extending outside the vessel, the conductor being electrically isolated from the conductive liquid and the conductive surfaces; 21 port in each end of the vessel; and connecting means comprising hydraulic lines connected between the vessel ports and the reservoir and pump outlet, at least one of said lines including a non-conductive segment leading into a respective one of the ports of the vessel.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A POTENTIOMETER COMPRISING: A VESSEL HAVING AN INNER SURFACE AND INCLUDING A CYLINDER AND A PAIR OF END CAPS CLOSING OFF THE ENDS OF THE CYLINDER; A PORTION OF SAID INNER SURFACE IN THE REGION OF ONE AND A PORTION OF SAID INNER SURFACE IN THE REGION OF THE OTHER OF THE END CAPS, SAID PORTIONS BEING CONDUCTIVE AND THE BALANCE OF THE INNER SURFACE BEING NON-CONDUCTIVE AND ELECTRICALLY ISOLATING THE CONDUCTIVE PORTIONS FROM EACH OTHER; MEANS FOR EFFECTING ELECTRICAL CONNECTION TO EACH CONDUCTIVE PORTION; A PISTON SLIDABLY MOUNTED IN THE CYLINDER AND DIVIDING THE VESSEL INTO TWO CHAMBERS, THE PISTON HAVING CONDUCTIVE, ELECTRICALLY CONNECTED FACES; A CONDUCTIVE LIQUID FILLING BOTH CHAMBERS, THE LIQUID IN ONE CHAMBER BEING ELECTRICALLY CONNECTED TO THE LIQUID IN THE OTHER BY THE PISTON FACES AND THE CONDUCTIVE FACES BEING ELECTRICALLY CONNECTED THROUGH THE LIQUID IN THE CHAMBERS AND THE PISTON FACES; A CONDUCTOR CONNECTED TO THE PISTON FACES AND ELECTRICALLY ISOLATED FROM THE LIQUID AND THE CONDUCTIVE SURFACES, SAID CONDUCTOR HAVING AN END EXTENDING OUTSIDE THE VESSEL; SAID CONDUCTOR HAVING A NON-CONDUCTIVE INNER SURFACE DEFINING A PASSAGE LEADING OUT OF THE CYLINDER IN THE REGION OF ONE OF THE END CAPS AND BACK INTO THE CYLINDER IN THE REGION OF THE OTHER OF THE END CAPS, THE PASSAGE BEING FILLED WITH THE CONDUCTIVE LIQUID.