US3913448A

US3913448A - Hydraulic actuator

Info

Publication number: US3913448A
Application number: US276369A
Authority: US
Inventors: Terence Patrick Priestley; John Duncan Garside
Original assignee: Loughborough University
Current assignee: Loughborough University
Priority date: 1971-08-04
Filing date: 1972-07-31
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: DE2238539A1; FR2149910A5; NL7210678A; GB1406987A; IT964884B; CH557909A

Abstract

A hydraulic actuator comprises a cylinder containing a doubleacting piston, a port adjacent each end of the cylinder and a piston-controlled intermediate port opened by the piston in moving to an intermediate position, each of the ports being connected to progressively adjustable valve means (for example a continuously rotatable valve means) coupled to operate in timed relationship to one another. The hydraulic actuator may also include a second cylinder containing a second piston which carries a probe extending axially into the first cylinder to abut the first-mentioned piston and having a port connected to continuously rotatable valve means arranged to operate in timed relationship to the first-mentioned valve means. There is also described a knitting machine including a plurality of needles, a separate hydraulic actuator for each needle of the machine, and on-off valve means for controlling supply of hydraulic fluid under pressure to the hydraulic actuators to operate hydraulic actuators in sequence to effect a knitting operation. The said valve means may be arranged to operate actuators of needles at spaced location simultaneously and the actuators of each of a number of groups of actuators sequentially. Each of the hydraulic actuators may be of the kind described above.

Description

United States Patent [1 1 Priestley et al.

[ Oct. 21, 1975 HYDRAULIC ACTUATOR [75] Inventors: Terence Patrick Priestley, Gotham;

John Duncan Garside, Loughborough,-both of England [73] Assignee: The Loughborough University of Technology, Loughborough, England 22 Filed: July 31,1972

21 Appl. No.: 276,369

[30] Foreign Application Priority Data Aug. 4, 1971 United Kingdom 36572/71 [52] U.S. Cl. 91/36; 91/39; 91/180; 91/230; 91/325; 91/357; 91/411 A;

[51] Int. CI. F15B 21/02 [58] Field of Search ..91/39,l80, 170, 219, 411, 91/411 A, 402, 325, 230,167 R, 167 A, 359,

[56] References Cited UNITED STATES PATENTS 785,611 3/1905 Hastings 91/180 2,661,724 12/1953 Blenkle.... 91/357 X 2,811,139 10/1957 Lado 91/180 2,882,685 4/1959 Carlsen et a1... 91/402 3,149,537 9/1964 Fink 92/62 3,253,515 5/1966 Wilkins0n.... 91/402 3,446,036 5/1969 Doughty 66/8 3,502,002 3/1970 Whiteman 91/402 FOREIGN PATENTS OR APPLICATIONS 655,606 l/1938 Germany 9l/l70 R Primary Examiner-Martin P. Schwadron Assistant ExaminerAbraham Hershkovitz Attorney, Agent, or Firm-Davis, Hoxie, Faithful] & Hapgood [57] ABSTRACT A hydraulic actuator comprises a cylinder containing a double-acting piston, a port adjacent each end of the cylinder and a piston-controlled intermediate port opened by the piston in moving to an intermediate position, each of the ports being connected to progressively adjustable valve means (for example a continu' ously rotatable valve means) coupled to operate in timed relationship to one another. The hydraulic actuator may also include a second cylinder containing a second piston which carries a probe extending axially into the first cylinder to abut the first-mentioned piston and having a port connected to continuously rotatable valve means arranged to operate in timed relationship to the first-mentioned valve means.

There is also described a knitting machine including a plurality of needles, a separate hydraulic actuator for each needle of the machine, and on-off valve means for controlling supply of hydraulic fluid under pressure to the hydraulic actuators to operate hydraulic actuators in sequence to effect a knitting operation. The said valve means may be arranged to operate actuators of needles at spaced location simultaneously and the actuators of each of a number of groups of actuators sequentially. Each of the hydraulic actuators may be of the kind described above.

9 Claims, 25 Drawing Figures U.S. Patet Oct. 21, 1975 Sheet4 0f5 3,913,48

US. Patent Oct. 21, 1975 Sheet 5 of5 3,913,448

lllllnl I7 g lll /9 will HYDRAULIC ACTUATOR This invention relates to the use of hydraulic actuators in knitting machines and to a hydraulic actuator of the piston and cylinder kind adapted to effect; controlled displacement of an actuating member to and from pre-selected positions and which can be employed in knitting machines or in other machines, particularly textile machines.

In a knitting machine, knitting is accomplished by steps which include displacing needles axially from retracted positions and subsequently returning them to their original positions. This displacement is normally effected by a cam system.

According to one aspect of this invention, a knitting machine includes a hydraulic actuator for each needle of the machine and on-off valve means for controlling supply of a hydraulic fluid under pressure to the hydraulic actuators to operate hydraulic actuators in sequence to effect a knitting operation.

The valve means may be arranged to operate actuators of needles at space locations simultaneously and the actuators of each of a number of groups of actuators sequentially.

Only one source of hydraulic fluid under pressure is needed and no pressure reduction devices, arranged to enable hydraulic fluid at a variety of pressures to be used, need be provided. Thus, the valve means may comprise means for controlling supply of hydraulic fluid from a single pressure source to the actuators and for controlling exhaust of fluid from the actuators.

Preferably, each actuator comprises a piston and cylinder device and may be rigidly connected to, or have a part integral with, the associated needle.

Advantageously, the valve means comprises a rotary valve having a member with ports which are arranged at intervals about a cylindrical surface of a further member having formed in it part-circumferential grooves arranged for cooperation with the said ports in the first-mentioned member and connected to supply and discharge ducts of the rotary valve, the said ports in the first-mentioned member being connected to the ports of actuators and the said first-mentioned member and the said further member being arranged for rotary movement relative to one another.

In some knitting machines, the needles can be operated selectively and each needle of the machine can be arranged to move from a retracted position to take up either of two other positions. Thus, a needle can be moved to a position such that it will retain a previously knitted loop and draw a new loop (the tuck position), orto a position such that it will cast off a previously knitted loop and then draw a new loop (the knit position). In addition, the needle can be left in its original position so that it will retain a previously knitted loop without drawing a new loop, (the miss position). Thus in some conventional knitting machines, the cam system is programmed selectively to displace needles axially from the miss position to either the tuck or knit position and to return them to the miss position in a pre-determined sequence, so as to produce a desired fabric construction.

A further aspect of this invention relates to a hydraulic actuator capable of displacing an actuator member to either of two positions and this hydraulic actuator is thus capable of employment in a knitting machine such as that just described.

According to this aspect of the invention, a hydraulic actuator comprises a first piston and cylinder device operable to displace an actuating member from a starting position to another position, and a second piston and cylinder device operable to displace the actuating member to said other position or to a different position, each cylinder having an exhaust port exposable by the associated piston and serving as a movement-limiting hydraulic stop therefor, and at least one of the piston and cylinder devices being a double-acting device whereby the actuating member may be returned to the starting position.

The invention also includes a knitting machine having needles operable by hydraulic actuators as just described. The hydraulic pressure for each piston and cylinder device is preferably obtained from a single, substantially constant pressure source, the supply of hydraulic pressure to the first and second piston and cylinder devices being controlled by at least one valve. Because only the three needle positions referred to above are required for most knitted fabric constructions, a hydraulic actuator as just described is particularly advantageous for effecting controlled axial displacement of a knitting machine needle and, when so used, is preferably arranged to operate directly on the needle by being directly connected thereto or having a part formed integral therewith. Conveniently, a large number of individual hydraulic actuators may be incorporated into a single block housing which may be mounted on or constitute the frame of a knitting machine.

One type of valve which can be used to control actuators of the kind just described, or which can be used in a knitting machine according to the first aspect of the invention, is a rotary valve in which circumferentially disposed grooves in the surface of a rotatable member communicate with stationary outlet ports for predetermined periods during each rotation of the rotatable member, the individual grooves being connected either to a source of hydraulic medium under pressure, or to a hydraulic sink. A single rotary valve of this kind may readily be adapted to operate a group of hydraulic actuators according to a pre-determined sequence. When applied to a knitting machine, it is convenient to arrange for the rotary member of the valve to be rotated by, and in synchronism with, the main drive mechanism of the knitting machine.

The hydraulic actuator which constitutes one aspect of this invention is basically a compound ram device incorporating a free piston and probe assembly which is not connected to the other piston and actuating member. The combination of a hydraulic actuator according to this invention with a rotary valve of the kind described is particularly advantageous in that it enables the achievement of a desired time-displacement curve for the actuator suitable for use in a specific application. Furthermore, because the rotary valve is capable of producing very rapid changes in hydraulic pressure, the actuator can be made to function at high speed.

According to yet another aspect of the invention, a hydraulic actuator comprises a cylinder containing a double-acting piston, a port adjacent each end of the cylinder and a piston-controlled intermediate port opened by the piston in moving to an intermediate position, each of the ports being connected to progressively adjustable valve means (for example continuously rotatable valve means) coupled to operate in timed relationship to one another. With this arrangement it is possible to select the characteristics of the flow from the cylinder through the intermediate port which is not the case with arrangements in which the flow is controlled only by the passage of the piston past the intermediate port. Firstly the timing of the flow through the intermediate port can be selected relative to the timing of the opening and closing of the ports adjacent the ends of the cylinder. Secondly the rate of increase of flow as the valve means opens and the rate of decrease of flow as the valve means closes can be selected by suitably designing the geometry of the valve parts. In other words the flow through the intermediate port can be timed and shaped as required. This enables the velocity, acceleration and deceleration of the piston, and of any parts mechanically connected to and positioned by the piston, to be selected. In certain arrangements the actual location of an intermediate stationary position of the piston can also be determined. A further design option may be introduced by the introduction of a selected hydraulic impedance downstream of the valve means. The ability to contol accelerations and decelerations and so avoid shock and the production of required velocity/time and position/time relationships for the piston are extremely valuable in high speed machinery such as knitting and other textile machines.

While the progressively adjustable valve means could take various forms such as a rotary cam-controlled spool valve, a continuously rotatable valve is preferred since this avoids the mechanical interface such as camto-cam follower present in most other forms of valve.

The hydraulic actuator may include a second piston which carries a probe extending axially into the first cylinder to abut the first-mentioned piston and having a port connected to continuously rotatable valve means arranged to operate in timed relationship to the firstmentioned valve means.

According to a still further aspect of the invention, a hydraulic system comprises a plurality of hydraulic actuators controlled by common valve means, each actuator comprising a cylinder containing a double-acting piston, a port adjacent each end of the cylinder and a piston-controlled intermediate port opened by the cylinder in moving to an intermediate position, and the common valve means being continuously rotatable and connected to control the flow through the ports of the actuators in a predetermined sequence This arrangement enables a large number of actuators to be controlled at high speed and in timed relationship to one another. It is particularly suited to actuators arranged in a circle in which case the valve means may advantageously be located to rotate about the axis of the circle.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section through a hydraulic actuator according to the invention,

FIG. 2 is a section through a rotary valve capable of operating the actuator of FIG. 1 according to a predetermined sequence,

FIGS. 3A, 3B, 3C and 3D are diagrammatic crosssections through the valve of FIG. 2, taken on the lines A-A, B-B, C-C and D-D of the latter, respectively,

FIGS. 4A, 4B, 4C and 4D are graphs showing the output pressure at the ports of the rotary valve of FIGS. 2

and 3 plotted against angle of rotation of the rotary member of the valve,

FIG. 5 is a schematic representation of a hydraulic circuit comprising the actuator of FIG. 1 and the rotary valve of FIGS. 2 and 3,

FIG. 6 is a graph showing the displacement of a knitting needle connected to the actuating member of the hydraulic actuator of FIG. 1 plotted against angle of rotation of the rotary member of the rotary valve controlling the actuator,

FIGS. 7A, 7B, 7C and 7D correspond generally to FIGS. 3A-3D, but show a valve port arrangement capable of operating eight actuators in sequence,

FIG. 8A-8D illustrates a valve port arrangement for operating 64 actuators in sequence,

FIG. 9 shows diagrammatically part of a hydraulic circuit for operating needles in a knitting machine, according to the invention,

FIGS. 10 and 11 show diagrammatically parts of another hydraulic circuit for operating needles in a knitting machine according to the invention,

FIG. 12 is a hydraulic circuit illustrating how successive displacements of a knitting needle may be programmed to follow a pre-chosen sequence, and

FIG. 13 is a diagrammatic cross-section through part of the rotary valve used in the circuit of FIG. 12, taken on the line XX of the latter.

In the hydraulic actuator of FIG. 1, a casing 1 defines a first cylinder 3 which extends axially of the casing, and a second cylinder 2 spaced from and lying on the same axis as the first cylinder. A narrow bore 4 along the common axis connects the two cylinders. Cylinder 2 contains a freely slidable piston 5 attached to a probe 6, which extends through the bore 4 into the second cylinder 3, in which is a freely slidable piston 11. The piston 1 1 is attached to an actuating member 12, which is constituted by a rod extending through an aperture in a detachable end plate 13 of the casing 1. An O-ring seal 14 is located in a groove in the end plate 13 to minimise leakage from the cylinder 3 along the actuating member 12.

The cylinder 2 has a port 17 for connection to a source of hydraulic fluid under pressure and a port 18 which is exposable by the piston 5, to form a hydraulic step for the latter as will be explained later.

The cylinder 3 has four

ports

19, 20, 21 and 22, whereby hydraulic fluid may be supplied to or may escape from the cylinder, as will be explained later.

The rotary valve of FIG. 2 comprises a stationary cylindrical casing 30 closed by

end plates

31 and 32, and containing a rotatable bobbin 33. The bobbin is cylindrical and has a drive shaft 34 which projects through an aperture in the end plate 31. The bobbin is a close fit in the casing 30, as is the drive shaft 34 in the end plate 31, annular seals 36 being located between the end plates and the ends of the bobbin.

A duct constituted by an axial bore 38 communicates with an aperture in the end plate 32, through which the bore 38, in use, is connected to a hydraulic sink containing fluid at a low hydraulic pressure, which is usually at or close to atmospheric pressure.

The casing has five axially spaced, parallel, radial bores which form

ports

39, 40, 41, 42 and 43. Each of the ports 40-43 is arranged to communicate in succession with two part-circumferential grooves in the bobbin 33 as the latter is rotated, eight part-circumferential.

grooves of various lengths being provided in all. In

FIGS. 3A-3D, the grooves associated with each of the ports 40-43 respectively are shown. The port 39 communicates with a single circumferential groove 44 in the bobbin, and in use is connected to a source of fluid under pressure (not shown).

As is evident from FIG. 3A, clockwise rotation of the bobbin 33 causes part-circumferential grooves 45A, 458 to be successively presented to the port 40. Likewise, as seen from FIGS. 3B-3D, part-

circumferential grooves

46A and 46B, 47A and 47B, and 48A and 48B are presented to their respective ports 4043 by rotation of the bobbin. In FIGS. 3A-3D part only of the casing 30 is shown for simplicity.

Each part-circumferential groove is connected either to the axial bore 38 by a radial bore 49, or to the circumferential groove 44 by a duct constituted by a short radial bore 50 and an axial bore 51, as indicated in FIGS. 3A-3D. As the axial bore 38 is connected through the end plate 32 to the sink, and is therefore effectively at atmospheric pressure, each of the ports 40-43 therefore communicates, when the valve is in use, either with the source of fluid under pressure, which is connected to the port 39, or with the sink (except when the ports are obscured by the narrow lands between adjacent ends of associated part-circumferential grooves).

FIGS. 4A4D are graphs of pressure (p) at the four ports 40-43 respectively plotted against angle of rotation (a) of the bobbin 33 in a clockwise direction (as viewed in FIGS. 3A-3D), from a bobbin starting position in which the bobbin has advanced slightly from the position shown in FIGS. 3A-3D. These pressures may be tabulated as follows, where P represents the pressure of the aforementioned source of fluid under pressure and E represents the exhaust pressure of the sink:

FIG. 5 shows the connection of the ports of the valve of FIGS. 2 and 3 to the ports of the actuator of FIG. 1, the reference numerals in FIG. 5 being the same as those used in FIGS. 1, 2 and 3. The valve port 39 and the axial bore 38 are connected to a source of fluid under pressure and to a sink, respectively. The

actuator ports

18 and 20 are connected to the sink.

Referring now to Table 1 in conjunction with FIGS. 1 and 5, rotation of the drive shaft 34 will cause the pressures and/or exhausts of Table 1 to be applied to the ports of the actuator during substantially the whole of the first quadrant, (over the width of the narrow lands between adjacent ends of associated part-circumferential grooves the pressure previously applied to the ports is approximately maintained). Thus inthe first quadrant, pressure is applied at the

actuator ports

17 and 19, while the

actuator ports

21, 22 are connected to exhaust.

The pistons 5 and 11 therefore move to the right (in FIG. 1) until the

actuator ports

18 and 20 are exposed by their associated pistons, allowing the hydraulic pressure to leak there from back to the sink. The

ports

18 and 20 thus act as movement-limiting hydraulic stops for the pistons 5 and 11 respectively. The actuating member 12 has now been displaced to its maximum possible extent towards the right in FIG. 1, and a space exists between the free end of the probe 6 and the piston 11.

In the second quadrant, pressure is applied to

actuator ports

17 and 22, while

actuator ports

19 and 21 are connected to the sink so that the piston 11 moves to the left in FIG. .1, until arrested by leakage of fluid from cylinder 3 through the port 21, when the latter is exposed by the piston 11. As the piston 11 comes to rest it also abuts the free end of the probe 6. The port 21 therefore acts as a movement-limiting hydraulic stop for return movement of the piston 11, in addition to the mechanical stop constituted by the probe member 6. At the end of the second quadrant, the actuating member 12 is partly retracted.

Further rotation of the bobbin 33 into the third quadrant causes pressure to be applied at

actuator ports

21 and 22, while the

ports

17 and 19 are connected to exhaust. The pistons 5 and 11 therefore move to the left in FIG. 1, and the actuating member 12 is fully retracted. Port 20 is uncovered by piston 11 as it approaches its limit of movement to the left in FIG. 1, thus reducing the pressure acting on the piston 11. The port 20 thus serves as a hydraulic stop for the leftwards movement of the piston 11.

In the fourth quadrant, the pressures and exhausts of the third quadrant are retained, so that the actuating member 12 dwells in the fully retracted position.

Further rotation of the bobbin 33 causes the above described cycle to be repeated. In FIG. 6, the displacement ((1) of an element, for example a knitting needle, connected to the actuating member 12 is plotted against the aforementioned angle of rotation (at) of the bobbin 33. In the first quadrant, the maximum displacement of the actuating member corresponds to a needle displacement k into the knit position. In the second quadrant the partly retracted position of the actuating member corresponds to a needle displacement 1 into the tuck position while in the third and fourth quadrants the fully-retracted position of the actuating member corresponds to a needle displacement m into the miss position, followed by a dwell in this position.

Advantageously, in a knitting machine, one rotary valve of the kind just described is used to operate several hydraulic actuators and their associated needles.

In the present description, several examples of knitting machines with arbitrarily chosen numbers of needles are given. This'invention can be applied to knitting machines with numbers of needles different from those given, the numbers of needles mentioned being chosen only for ease of illustration. The invention is applicable to any form of'knitting machine having independently operable needles such as circular and V-flat machines riphery of a stationary cylinder around which a yarn carrier mechanism is rotated to supply yarn to the needles in sequence. FIGS. 7A-7D illustrate how sequential operation of several hydraulic actuators may be accomplished by providing the rotary valve of FIGS. 2 and 3A-3D with eight sets of ports (shown by radial lines in FIG. 7) corresponding to the set of ports 4043. Each set of ports 40-43 is arranged in a line parallel to the axis of the valve, but the sets are equally spaced around the circumference of the casing 30. Each set of four ports is connected to a separate actuator, in the manner of FIG. 5, and the sets of ports are numbered 40,, 41 42 43,; 40 41 42 43 and so on to 40 41 42 43 Clockwise rotation of the bobbin 33 causes the pressures and exhausts of Table 1 to appear at each set of ports in turn, causing the eight actuators successively to displace their needles through the cycle of FIG. 6.

The number of actuators thus controlled may readily be increased as desired, up to the limits set by the diameter of the casing 30 and size of the pipe fittings employed. Beyond these limits,- the rotary valve can be enlarged to operate an even larger number of hydraulic actuators in sequence by providing the valve with further sets of part-circumferential grooves and with corresponding further sets of ports axially displaced from the first-mentioned sets.

FIGS. 8A8D illustrate this scheme applied to a system in which one rotary valve controls 64 actuators in sequence.

The valve illustrated in FIGS. 8A8D has a valve bobbin having four axially spaced sets of four pairs of part-circumferential grooves, each set of grooves corresponding to the single set of pairs of grooves associated with the ports 40-43 of FIGS. 2 and 3A-3D. The valve also has 16 sets of four ports for each set of grooves, making 256 ports in all, 64 ports being associated with each set of grooves. FIGS. 8A8D show the 64 ports associated with the first pair of part-circumferential grooves of each set of grooves, the individual ports being indicated by radial lines and designated by the numerals 40 -40 The 16 ports associated with each pair of part-circumferential grooves are equally spaced around the valve casing and the ports associated with the sixteen pairs of part-circumferential grooves are located in corresponding positions around the circumference of the valve so that each set of ports is arranged along a line parallel to the axis of the valve and three other sets of ports are also arranged along the same line. However, successive sets of grooves are progressively displaced circumferentially of the bobbin, through an angle /4, 0 being the angle subtended at the axis of the bobbin by any two adjacent ports of a group of 16 ports. Because of the progressive angular displacement of 0/4 from one set of grooves to the next, clockwise rotation of the valve bobbin will result in each one of the 64 ports shown in FIGS. 8A8D being connected successively to one or other of the four part-circumferential grooves having leading edges 65 65 65 65., in the order indicated by the numbering of ports 40 to 40 inclusive. The 64 ports of the second group of 64, which are associated with the second pairs of part-circumferential grooves of each set of grooves will also be connected successively with one or other of the associated grooves and similarly for the ports of the remaining two groups of 64 ports. In this way, the 64 actuators are actuated in sequence.

25, 37 and so on up to 133..Each of the ports 67 to To summarise, a complete valve for operating 64 actuators in sequence would therefore have 16 pairs of part-circumferential grooves and 16 ports for each pair of grooves, successive sets of four pairs of grooves being displaced progressively through 0/4 relative to the adjacent set or sets. Each actuator would be connected to the valve as shown in FIG. 5.

The valve just described is suitable for operating a single feeder knitting machine with 64 needles which are operated in sequence. However, to take full advantage of the increase in knitting rates which is possible by applying the present invention to a knitting machine, it is necessary to use the invention in a multifeed machine in which the feeders are spaced more closely than is possible using conventional cam operation of the needles. In a conventional cam-operated machine the smallest distance apart at which it is possible to locate the feeders is governed by the maximum possible angle of the cams which raise the needles to take yarn at the feeders. If the cams are too steep, the forces exerted on the needle butts in accelerating the needles up the steep cam slopes are so great that the butts are broken off at too high a rate to be acceptable under commercial conditions. By employing the present invention in a knitting machine, the needles can be raised much more quickly, than is possible by means of cams, and in fact a rate of needle rise equivalent to using a cam angle of nearly can be achieved. The number of needles associated with each feeder, in the sense of the number of needles which are at any instant moving up to take yarn at the feeder and moving down away from the yarn feeding point, can thus be greatly reduced. If each needle is required to dwell at a tuck height in its downward movement, then two needles must be associated with each feeder, but if the needles are allowed to execute a simple up-and-down movement without dwell, then it would be possible to supply yarn simultaneously to each needle of a hydraulically actuated knitting machine and to operate the needles simultaneously.

A hydraulic circuit for a circular knitting machine having 144 needles and twelve feeders so that twelve needles are associated with each feeding operation is shown diagrammatically in FIG. 9. A rotary valve 65 similar to that of FIG. 2 is used having twelve sets of four

ports

66, 67, 68 and 69, and inlet port 39 for fluid under pressure and an exhaust bore 38 for fluid. The valve 65 is such that on rotation of the valve shaft 34 the pressure at the four ports of each set of ports is varied in such a way as to effect actuation of an actuator as described with reference to FIG. 1 in the manner described with reference to FIGS. 4 and 6. Each needle in the machine is directly connected to, or integral with, the actuator member of an actuator as shown in FIG. 1. The 12 sets of ports of the rotary valve 65 are spaced at intervals of 30 around the circumference of the rotary valve (each set of ports being arranged along a line parallel to the axis of the valve).

The four ports of only one of the 12 sets are shown in FIG. 9. Each of the ports 66 to 69 is connected to an appropriate port of each of 12 actuators located at equidistantly spaced intervals around the circumference of the knitting machine. In FIG. 9, the port 66 of the rotary valve 65 is shown having connections leading to the appropriate ports of 12 needle actuators l, 13

69 is similarly connected to the appropriate ports of the same actuators. The ports of the next set of ports 66 to 69 on the rotary valve are connected to the appropriate ports of l2 actuators 2 14, 26 and so on and the next set of ports on the rotary valve is connected to actuators 3 27 and so on, the next set to actuators 4, 16 28 and so on, so that each set of ports on the rotary valve operates 12 actuators simultaneously and the 12 sets of ports around the rotary valve cause the actuators of each of 12 groups of actuators to be operated in sequence. In a knitting machine with a stationary needle cylinder, the rotary valve 65 would be driven at 12 times the speed of the yarn carrier mechanism so that yarn is taken by each needle from each of 12 yarn supply points on the mechanism during one revolution of the yarn carrier thus producing 12 courses of knitting during each revolution of the yarn carrier mechanism.

Another hydraulic circuit for a multi-station circular knitting machine is shown diagrammatically in FIGS. 10 to 11. FIG. 10 shows a section through a rotary valve 74 similar to that described with reference to FIG. 2, which valve is connected to a source of hydraulic fluid through a port 39 and to a sink through a bore 38. In the valve of FIG. 10 and 11, however, the part-circumferential grooves have been shortened and their number has been increased so that instead of a single set of four pairs of pressure and exhaust grooves, the valve has four sets of four pairs of grooves, the sets of grooves being located in successive positions around the rotatable bobbin 33 of the valve, each set of grooves being contained in a different quadrant.

FIG. 10 shows four pairs of

grooves

80, 81, 82 and 83 each pair of grooves shown being one of the pairs of grooves of a different one of the four sets of grooves. The exhaust groove of each pair is connected to the common exhaust bore 38 and the pressure grooves of the pairs of grooves shown are connected to separate

bores

51,, 51 51 51 the pressure grooves of any one set communicating with the same bore 51 51 51:, or 51., and all the bores 51 communicating with a source of fluid under pressure through a groove 44 and port 30 as shown in FIG. 2.

The rotary valve has 48 sets 75 to 75 of four

ports

76, 77, 78 and 79 (FIG. 11) corresponding to the

ports

40, 41, 42 and 43 of FIG. 2. Each set of ports 76 to 79 is connected to the appropriate ports of an actuator as shown in FIG. 1, successive sets of ports around the valve being connected to successive actuators around the circumference of a 48 needle knitting machine. Thus on rotating the shaft 34 of the rotary valve 74 at the same angular speed as the yarn carrier mechanism of the knitting machine, the actuators will be operated in such a way that actuators spaced at intervals of 12 needles around the circumference of the machine will move through identical time displacement profiles, as shown in FIG. 6, in phase with each other. Each needle of the knitting machine will therefore be actuated four times in each revolution of the yarn carrier mechanism which is provided with four feed points.

The arrangements so far described for operating one or more of the hydraulic actuators of FIG. 1 have only been capable of producing a time-displacement profile of the kind shown in FIG. 6, which in a knitting process, would produce a plain-knit fabric. However, in order to produce patterned fabric it is desirable to have a facility whereby a given needle of the knitting machine will successively knit, tuck or miss, according to a prechosen sequence.

In the hydraulic circuit of FIG. 5 it is only necessary to prevent pressure pulses reaching the

actuator ports

17 and 19 in order to obtain the miss condition, and to prevent a pressure pulse reaching the actuator port 19 to obtain the tuck condition. One way of achieving this would be to connect an electrically-operated solenoid valve in series with each of the respective connections between the

valve ports

42 and 43, and the

actuator ports

17 and 19. However, because the operating speeds of solenoid valves are limited, advantageously,

the circuit shown in FIG. 12, which is a modified version of the circuit of FIG. 5, is used. In this Figure, parts corresponding to parts shown in FIG. 5 bear the same reference numerals. Each of the

ports

17, 19, 21 and 22 of the actuator having a casing 1 is connected to a rotary valve having a casing 30 by four separate paths each connected to a separate port of the rotary valve. The valve casing 30 has four sets of

ports

40 and 43 equally spaced about its circumference and the four paths leading to actuator port 17 are connected to valve ports 40A to 40D. The

actuator ports

19, 21 and 22 are connected to

valve ports

41, 42, and 43,, respectively. Each set of four paths is brought together in respective manifold block 53-56, from each of which blocks a single connection is taken to the appropriate actuator port. Thus it is possible to operate the actuator four times every one revolution of the valve bobbin by modifying the valve of FIG. 2 and FIGS. 3A-3D so that the part-circumferential grooves associated with each of the four ports 40-43 occupy only one quadrant of the circumference of the valve bobbin. Such an arrangement is illustrated by FIG. 13, which shows one pair of grooves 45A, 458 only. By providing the valve of FIG. 13 with four

outlet ports

40A, 40B, 40C and 40D respectively at intervals around the valve casing, each complete rotation of the valve bobbin would, with the valve in the circuit of FIG. 5, simply cause the actuator to go through the cycle of operations shown in FIG. 6 four times. However, in FIG. 12, each of the four paths to each of the

actuator ports

17 and 19 is passed through a respective patterning block 57-60 or 61-64 before it is taken to the

manifold block

53 or 54.

Each of the patterning blocks 57-64 acts as a valve which may be opened or closed in order to open or close any one path to an actuator. Conveniently, each patterning block comprises a pair of abutting flanged pipe connections, with a plastic disc sandwiched between them, the discs being imperforate to close a path, and having an aperture to allow fluid to pass along a path. By selecting which paths are open and which closed, the movements of an actuator over successive sets of four operations can be predetermined.

A one-way valve 52 is connected between the

actuator ports

17 and 19 so that hydraulic fluid trapped in the cylinder 3 (see FIG. 1), between the piston 11 and the port 19, can be exhausted when the piston returns from the tuck displacement to the miss position. This condition occurs when the actuator is programmed to tuck, because the associated supply line is closed by the patterning block.

What is claimed is:

1. A hydraulic actuator comprising a first cylinder containing a first double-acting piston, first and second ports each adjacent a different end of said first cylinder and piston-controlled port means intermediate the ends of said first cylinder opened and closed by said first piston in moving between the ends of said first cylinder, said first and second ports being connected to first and second sequential valve portion controlled ports in a housing independent of the actuator and respectively controlling connection of said first and second ports in a predetermined sequence to a source of pressurized hydraulic medium and to exhaust, said pistoncontrolled port means including a first pistoncontrolled port connected to a third sequential valve portion controlled port in said housing, a second cylinder aligned end-to-end with said first cylinder and containing a second piston, a probe slidable relative to the cylinders and extending from the first cylinder to the second cylinder to prevent the two pistons moving closer to one another than a predetermined minimum, said second cylinder having a third port connected to a fourth sequential valve portion controlled port, and coupling means in said housing connecting said first, second, third and fourth valve portions to insure operation of each valve portion in. timed relationship with the other three valve portions.

2. A hydraulic actuator as claimed in claim 1, in which the third port of said second cylinder is adjacent one end of the latter, said second cylinder also having a second piston-controlled port means opened and closed by said second piston in moving between the ends of said second cylinder.

3. A hydraulic actuator as claimed in claim 2, including an actuating member connected to said first piston for movement between two end positions, and wherein said second piston is operable through the intermediary of said probe for moving said first piston to position the actuating member in a third position intermediate said two end positions.

4. A hydraulic actuator as claimed in claim 3, in which said piston-controlled port means of said first cylinder further includes a third piston-controlled port which, when opened by said first piston, connects one of said first and second ports to exhaust when said first piston is in a position corresponding to one of said end positions of the actuating member.

5. A hydraulic actuator as claimed in claim 4, in which said first piston-controlled port of said first cylinder, when opened by said first piston, connects said second port to exhaust when said first piston is in a position corresponding to said third position of the actuating member.

6. A hydraulic actuator as claimed in claim 1, including means for continuously rotating the four sequential valve portions.

7. A hydraulic actuator as claimed in claim 1, in which said four sequential valve portions are assembled in a unit which is mounted in a common casing and means for rotating said unit.

8. A hydraulic actuator as claimed in claim 1, in which said probe is carried by one of the pistons and extends axially into the cylinder of the other piston to abut the other piston.

9. A hydraulic actuating system comprising a plurality of hydraulic actuators as claimed in claim 1, in which said coupling means is common to the sequential valve portions of all the actuators, whereby all the valve portions are operated in timed relationship with one another.

Claims

1. A hydraulic actuator comprising a first cylinder containing a first double-acting piston, first and second ports each adjacent a different end of said first cylinder and piston-controlled port means intermediate the ends of said first cylinder opened and closed by said first piston in moving between the ends of said first cylinder, said first and second ports being connected to first and second sequential valve portion controlled ports in a housing independent of the actuator and respectively controlling connection of said first and second ports in a predetermined sequence to a source of pressurized hydraulic medium and to exhaust, said piston-controlled port means including a first piston-controlled port connected to a third sequential valve portion controlled port in said housing, a second cylinder aligned end-to-end with said first cylinder and containing a second piston, a probe slidable relative to the cylinders and extending from the first cylinder to the second cylinder to prevent the two pistons moving closer to one another than a predetermined minimum, said second cylinder having a third port connected to a fourth sequential valve portion controlled port, and coupling means in said housing connecting said first, second, third and fourth valve portions to insure operation of each valve portion in timed relationship with the other three valve portions.