US3131603A

US3131603A - Servomotor systems

Info

Publication number: US3131603A
Application number: US174803A
Authority: US
Inventors: Hadekel Ruben
Original assignee: Sperry Gyroscope Co Ltd
Current assignee: Sperry Gyroscope Co Ltd
Priority date: 1961-02-24
Filing date: 1962-02-21
Publication date: 1964-05-05
Anticipated expiration: 1981-05-05

Description

y 5, 1964 R. HADEKEL 3,131,603

SERVOMOTOR SYSTEMS Filed Feb. 21, 1962 2 Sheets-Sheet 2 RUBEN HADEKEL United States Patent Ofiice 3,131,603 Patented May 5, 1964 3,131,603 SERVOMOTOR SYSTEMS Ruben Hadekel, London, England, assignor to The Sperry Gyroscope Company Limited, Brentford, England, a company of Great Britain Filed Feb. 21, 1962, Ser. No. 174,803 Claims priority, application Great Britain Feb. 24, 1961 6 Claims. (Cl. 91-165) This invention relates to servomotor systems and is particularly but not exclusively applicable to such systems for use in aircraft, for example, for moving a control surface. In such applications it is often desirable to make provision for alternative operational mode means, such as manual means, to perform the task of the servomotor-s in certain circumstances. The occurrence of a breakdown or fault in the servomotor system or in an automatic pilot controlling the system are examples of such circumstances. In order to avoid interference with the operation of the alternative means by the servomotors it is often the practice to provide a mechanical connection between the servomotors and the control surface or other load member which can be disconnected when the alternative means is in operation. One object of the present invention is to provide a new and simple means of effectively disconnecting servomotors from a load member so as to make possible or facilitate the movement'of the load member by alternative means.

According to the invention, the improved servomotor system includes a fixed frame, a pair of cooperating pressure jacks having axially spaced cylinders fixed mounted on the frame and respective oppositely arranged pistons with effective and ineffective modes of operation, a load member movably mounted on the frame between the pistons, .and alternative means providing the operational mode of the pistons. The range determining means in the improved system includes mechanical means for connecting the load member to the pistons in their effective mode of operation having a first part of fixed length between the load member and one of the pistons and a second part of a length equal to the length of the first part between the load member and the other of the pistons. The alternative mode range determining means further includes means for biasing the pistons in their ineffective mode of operation. The improved system also includes change-over means operable to overcome the bias of the biasing means and provide a diiferential pressure input to the cylinders of the jacks to move the load member through the connecting mechanical means and pistons.

In one embodiment of the invention, the mechanical connecting means of the combination is a rocker pivoted on the load member with respective free arms of equal length whose ends operatively engage the respective pis tons in their etfective mode of operation. Here, the biasing means provided are springs that are effective to separate the respective pistons from engagement with the free ends of the rocker.

In another embodiment of the invention, the mechanical connecting means is a flexible cable with parts of equal length between the load member and the respective piston. Here, the included baising means are springs that are elfective to release the tension in the cables connecting the load member and pistons. In order that the invention may be clearly understood and readily carried into practice, a specific embodiment and a modification will now be described, by way of example, with reference to the drawings accompanying the provisional specification, in which:

FIGURE 1 is a part-schematic, part cross-sectional view of a servomotor system conducted in accordance with the invention, and

FIGURE 2 is a part cross-sectional view of a modification of the embodiment shown in FIGURE 1.

Referring now to the arrangement shown in FIGURE 1, the improved servomotor system there shown comprises a pair of hydraulic jacks, exemplified by the jack cylinders 1, 2 with their pistons 3, 4, which have hydraulic fluid applied to or exhausted from them through apertures 7, 8. The pistons 3, 4 are carried on piston rod members 5, 6. The cylinders 1, 2 of the jacks are fixed mounted on a frame 46 in axially spaced relation.

The differential fluid pressure input to the jacks moves the pistons 3, 4 towards a pivoted load member 16 against the action of springs 9 and 10 which are arranged to bias the pistons away from the load member. The movable load member is mounted on a frame 46 between the pistons 3, 4. The load member 16 includes a mechanical connecting means consisting of a rocker 11 with two arms or push rods 12, 13 of equal length which are received in

recesses

14, 15 in the piston rod portions 6, 5 respectively, the rocker being pivoted to the load member by means of pivot 17. The load member 16 is pivoted to the frame 46 at 18 and its motion is transmitted to other members by way, for example, of connecting rods or cables 19. The pistons 3, 4 of the hydraulic jacks are arranged to be moved by hydraulic fluid applied to them under the control of a common servo control valve 20. Between the servo control valve 20 and the jacks 1, 2 is an engaging valve 21, the purpose of which is to allow hydraulic fluid in the jacks to escape to hydraulic fluid reservoir 34 when it is desired to move the load member 16 by means other than the jack pistons 3 and 4.

The engaging valve 21 comprises a cylinder 22 containing a piston member having three

lands

23, 24, 25 forming between them two

annular chambers

26, 27 which are movable along the cylinder to vary the hydraulic fluid path to connect

hydraulic lines

30, 31 leading to the jacks 2, 1, selectively to

hydraulic lines

32, 33 leading to the hydraulic fluid reservoir 34 or

hydraulic lines

28, 29 which are connected to servo control valve 20. The hydraulic fluid is drawn from this reservoir 34 by the pump 35 from which it is fed to the servo control valve 20.

The piston member in the cylinder 22 is movable axially of the cylinder between two limits, and is biassed towards one of these limits, namely the right-hand one as shown in the drawing, by means of a spring 36. At this limit the

lines

30, 31 are connected to the

lines

32, 33 through the

annular chambers

27, 26 respectively. In normal operation the engaging valve 21 is held against the bias of spring 36 by means of the solenoid 37, so that the

lines

28, 30 are connected together through annular chamber 27 and the

lines

29, 31 are connected together through annular chamber 26. The solenoid 37 may be controlled either manually or automatically, thus, means may be provided for automatically de-energising the solenoid in the event of a fault occurring in the hydraulic system. In a modification, the piston member in the cylinder 22 is arranged to be moved hydraulically instead of electromagnetically, for example by applying hydraulic fluid under pressure from the pump 35 to the right-hand end face of the land 25.

The servo control valve 20 receives hydraulic fluid under pressure from pump 35 and, according to the position of its valve member 20a, varies the output pressure in

lines

28 and 29 differentially between a value a little less than the output pressure from pump 35 and a value much less than the pump output pressure but sufficient, if applied to one of the jacks, to move the piston through its full range of movement in opposition to the force of spring 9 or spring 10 alone. Thus when the engaging Valve 21 is held against the bias of spring 36 by energisation of the solenoid 37, and the lines 28, 3t) and 23, 31 are connected by way of the

annular chambers

27 and 26, these pressures reach the jacks 2, 1. The pressures are, in normal operation, always sufficient to maintain the piston rod portions 6 and in operative engagement with the ends of the rocker arms 12 and 13 of the connecting means determining the eifective mode of operation of the pistons. Motion of the load member 16 occurs through the connecting mechanical means and pistons brought about by the suitable positioning of the valve member 20a of valve 20 and its resulting difierential pressure output.

Here when the valve 21 is operated to bring rocker 11 under the control of the hydraulic system, the piston rod members 6 and 5 may not engage the arms 12 and 13 simultaneously. To avoid or minimise jolting or erroneous movement of the load member in the interval which elapses before both piston rod members are engaged by the corresponding arms, a pick-off device is provided having one part 38 fixedly mounted on rocker 11, and another part 39 fixed to an arm 47 which is movable with respect to part 38 and urged by suitable resilient means 33a into a yieldably centered condition with respect to part 38. Part 39 carries two resilient feeler members 40 and 41 which are so positioned as to be engaged by the piston rod members just before the latter are in full engagement with arms 12 and 13 of the rocker 11.

A comparatively strong output signal from this pickoff device is applied to input terminals of an amplifier 42 the output signal of which is arranged to control the servo control valve 20. Other input terminals of the amplifier 42 have applied to them a position demand signal from a position setting device 43 and a position feedback signal from a further pick-off device 43a associated with the load member 16.

During the process of bringing the load member under the control of the hydraulic system, the output signal from the pick-01f device 38, 39 is added to the other two signal inputs to the amplifier 42. If, for example, the piston rod portion 5 is in advance of the piston portion rod 6 as they are being brought into engagement with the ends of the arms 13 and 12 of rocker 11 the resilient arm 41 will be contacted by the piston rod portion 5 and part 39 of the pick-off device will be moved from its position of symmetry to produce a bias signal in such a sense that the pressure in jack 1 is reduced and that in jack 2 increased. This will result in a speeding up of the advance of piston 4, and a reduction in any force exerted by piston 3 upon the load member. In this way the piston rod portions 5 and 6 are brought into engagement with the load member 16 without appreciably disturbing it. A switch (39a) is provided for cutting out the signal from the pick off when full engagement is attained. To prevent such erroneous operation of the system during the interval before the cut out switch is operated as might be caused by a lack of symmetry in the pick-off arrangement, the pick-off may be provided with a dead spot at the centre of its range. This can be readily provided in an E-type pick-01f by very slightly increasing the length of the armature member 39 in relation to the length of the E-shaped core member 38.

Part of an alternative arrangement is shown in FIG- URE 2 of the drawings. Here the load member 16 is also pivoted at 18 on the frame 46 and the piston rod portions 5, 6 are connected to it through flexible members, such for example as the cables 45, 44. Application to the jacks, 1, 2 of hydraulic fluid under pressure through the

lines

31, 30 moves the pistons 3, 4, and with them the piston rod portions 5, 6, away from the member 16 against the bias of the springs 9, 10. This movement serves to tension the cables 45, 44 and so transmit the forces acting on the pistons 3, 4 to the member 16. When the pressure of the hydraulic fluid applied to the jacks through the

lines

30, 31 falls below the value required to overcome the bias of the springs 10, 9, the pistons and their associated piston rod portions are moved towards the arm 16, so slackening the cables 44, 45 and allowing movement of said member 16 independently of the servomotor system. It will be appreciated that the distance between the ends of the piston rod portions 5, 6 when fully extended from the jacks 1, 2 under the bias of springs 3, 10 is such that sufiicient room is left to enable the member 16 to be moved over the desired range. Here, the cables 44, 45 provide connecting parts of equal lengths between the load member 16 and the respective pistons that are included in the alternative mechanical connecting means of the system for determining the effective and ineffective modes of operation of the pistons.

While a hydraulic arrangement has been described by way of example, the invention could equally well be applied to a pneumatic arrangement.

What is claimed is:

1. A servomotor system of the character described including a fixed frame, a pair of cooperating pressure jacks having axially spaced cylinders fixedly mounted on the frame and respective oppositely arranged pistons with effective and ineffective modes of operation, a load member movably mounted on the frame between the pistons; alternative means providing the operational mode of the pistons including mechanical means for connecting the load member to the pistons in their efiective mode of operation having a first part of fixed length between the member and one of the pistons and a second part of a length equal to the length of the first part between the member and the other of the pistons, and means for biasing the pistons in their ineffective mode of operation; and changeover means operable to overcome the bias of the biasing means and provide a difierential pressure input to the cylinders of the jacks to move the member through the connecting mechanical means and pistons.

2. A system as claimed in claim 1, in which the load member is pivotally mounted on the frame, and the mechanical connecting means is a rocker pivoted on the member with respective free arms of equal length whose ends operatively engage the respective pistons in their eifective mode of operation.

3. A system as claimed in claim 1, in which the load member is pivotally mounted on the frame, and the mechanical connecting means is a flexible cable with parts of equal length between the load member and the respective pistons.

4. A system as claimed in claim 2, including an arm movably mounted on the load member having feelers arranged to engage the respective pistons, means for yieldably centering the arm with respect to the load member, and a pick-off providing an input to the system having a part fixed to the arm and a part fixed to the rocker.

5. A system as claimed in claim 2, in which said pis ton biasing means are springs effective to separate the respective pistons from engagement with the free ends of the rocker.

6. A system as claimed in claim 3, in which said piston biasing means are springs effective to release the tension in the cable connecting the load member and pistons.

References Cited in the file of this patent UNITED STATES PATENTS 2,380,510 Fitch July 21, 1945 2,400,233 Hicks May 14, 1946 2,630,785 Ray Mar. 10, 1953 2,987,048 Buxton et a1 June 6, 1961

Claims

1. A SERVOMOTOR SYSTEM OF THE CHARACTER DESCRIBED INCLUDING A FIXED FRAME, A PAIR OF COOPERATING PRESSURE JACKS HAVING AXIALLY SPACED CYLINDERS FIXEDLY MOUNTED ON THE FRAME AND RESPECTIVE OPPOSITELY ARRANGED PISTONS WITH EFFECTIVE AND INEFFECTIVE MODES OF OPERATION, A LOAD MEMBER MOVABLY MOUNTED ON THE FRAME BETWEEN THE PISTONS; ALTERNATIVE MEANS PROVIDING THE OPERATIONAL MODE OF THE PISTONS INCLUDING MECHANICAL MEANS FOR CONNECTING THE LOAD MEMBER TO THE PISTONS IN THEIR EFFECTIVE MODE OF OPERATION HAVING A FIRST PART OF FIXED LENGTH BETWEEN THE MEMBER AND ONE OF THE PISTONS AND A SECOND PART OF A LENGTH EQUAL TO THE LENGTH OF THE FIRST PART BETWEEN THE MEMBER AND THE OTHER OF THE PISTONS, AND MEANS FOR BIASING THE PISTONS IN THEIR INEFFECTIVE MODE OF OPERATION; AND CHANGEOVER MEANS OPERABLE TO OVERCOME THE BIAS OF THE BIASING MEANS AND PROVIDE A DIFFERENTIAL PRESSURE INPUT TO THE CYLINDERS OF THE JACKS TO MOVE THE MEMBER THROUGH THE CONNECTING MECHANICAL MEANS AND PISTONS.