Air Cylinder

Abstract

An air cylinder whose piston has a male boss and a female recess which are coaxial and which coact with complementary female recess and male boss, respectively, on the relevent end caps to provide cushioning. Two air ports are formed in each end cap and connecting tubes connect the air port in one end cap to the opposite end of the cylinder via the other end cap. The air ports not required are blanked off with screwed plugs. Thus, air connections can be made to either end cap.

Description

This invention relates to cushioned air cylinders of tie-rod construction.

The present invention consists in a cushioned air cylinder of tie-rod construction which includes a cylinder barrel whose open ends are closed in a fluid-tight manner by end caps, a piston rod extending through one of said end caps and having one end thereof connected to a piston which is located within said cylinder barrel for reciprocating movements therealong under the influence of super-atmospheric fluid pressure, said air cylinder having a plug seal cushioning system which is provided on the one hand by the piston having axially aligned male and female portions of which the male portion carries an annular seal and on the other hand by the end caps of which one is provided with a female cushion bore and of which the other is provided with a male boss carrying an annular seal.

Preferably, said one end of the piston rod extends through or into the male portion of the piston. Said one end of the piston rod may extend into said piston over an axial distance substantially equal to the length (axially of said piston) of the boss which constitutes said male portion of the piston, said one end being bored and tapped for the reception of a screw which extends from a location within said female portion of the piston through a hole in said piston into said piston rod.

Again, preferably, each end cap is provided with air ports of which one is in communication with that end of the cylinder barrel with which said end cap is associated and of which the other is in communication with that end of the cylinder barrel with which the other end cap is associated. The communication between said other air port in each end cap and that end of the cylinder barrel with which the respective other end cap is associated may be established by a conduit which extends externally of said barrel between said end caps.

The annular seals carried by the male portion of the piston and by the male boss of the respective end cap are preferably V-rings or lip seals. Moreover, the piston is further provided with axially spaced annular seats for annular V-rings or lip seals which are placed in back-to-back positioning relative to one another.

Each end cap is provided in the usual manner, with cushion adjusting screws and is also appropriately bored or otherwise formed to provide bleed passages therethrough for the air being "compressed" by the movement of the piston.

The provision of a standard or uniform end cap casting or stamping reduces original tooling costs and raw material inventory.

The provision of standard air ports in each end cap permits the addition, at either end of the air cylinder at the choice of the user or as dictated by other factors, of the solenoid valve assembly which is disclosed in U.S. Pat. application Ser. No. 47,666, filed June 19, 1970, now U.S. Pat. No. 3,688,799, directly to the air cylinder and without any of the usual ancillary piping.

The cushioned air cylinder of tie-rod construction described above may advantageously be such that said piston rod is prevented from rotation about its longitudinal axis by virtue of the inner end portion of said piston rod being fixedly secured to the piston assembly and by virtue of the piston assembly being movable with reciprocating motion in the cylinder under the influence of said fluid at super-atmospheric pressure on and along a non-circular section location rod, the arrangement being such that any tendency of said piston rod and of the piston assembly fixedly secured thereto to rotate about said longitudinal axis is positively prevented by said piston assembly being slidably connected to said location rod by way of a passageway in the piston assembly, at least a portion of said passageway having a section complementary to that of the location rod which extends therethrough.

In a preferred embodiment of said air cylinder, the longitudinal axes of the location rod and the piston rod are coincident, at least a part of the length of said location rod being accommodated at all times within the piston rod which is hollow; said piston rod will need to accommodate the whole of the free part of the location rod during the respective one of the two strokes of the piston assembly.

In said preferred embodiment, one end of the location rod is fixedly secured to that end cap of the air cylinder through which the piston rod does not extend. Furthermore, the piston assembly includes a disc or location rod bearing which is made of a material having a low coefficient of friction (for example, DELRIN or TUFNOL, Registered Trade Marks), said disc being fixedly secured to the piston to form part of the piston assembly and having said passageway of non-circular section formed therethrough. The passageway and the location rod are preferably of square section.

The present invention will now be more particularly described with reference to the accompanying drawings, in which:

FIG. 1 illustrates in top plan an air cylinder constructed in accordance with the present invention;

FIG. 2 illustrates a longitudinal or axial section of the air cylinder of FIG. 1, said air cylinder having been turned through 90.degree. about its axis from the position thereof illustrated in FIG. 1;

FIG. 3 illustrates diagrammatically one of the end caps of the air cylinder;

FIG. 4 illustrates the modification applicable to the air cylinder illustrated in FIGS. 1, 2 and 3 whereby the ram or piston rod is not rotatable relative to the cylinder barrel; and

FIG. 5 illustrates, in a detail view, the manner in which one of the end caps of the air cylinder can be modified to support a limit switch unit.

Referring firstly to FIGS. 1 to 3, there is illustrated therein an air cylinder which comprises an aluminium alloy cylinder barrel 10 into whose open ends are inserted two aluminium alloy end caps indicated generally by the reference numerals 11, 12.

It will be noted from FIG. 2 that, as regards their general shapes and overall dimensions, the end caps are very similar, each having a male boss and a female recess coaxial therewith and this arises from the fact that the design of the whole air cylinder is based on the provision of a standard or uniform end cap casting or stamping which is then, by or in the course of further unit operations, made into either a so-called front end cap like the end cap 11 or a so-called rear end cap like the end cap 12. The ability to stock a standard end cap saves considerable sums of money by reducing original tooling costs and raw material inventory; by contrast, the need to stock two different types of end cap for the manufacture of air cylinders increases those tooling costs and inventory and could lead to accidental stock exhaustion of one particular end cap.

The air cylinder further comprises an aluminium alloy piston 13 which consists of a right-cylindrical portion 14 having a male boss 20 and a female recess 21, the boss 20 and the recess 21 being coaxial. The portion 14 is bored at 22 and the boss 20 is counterbored at 23 for a reason which will become apparent. Circumferentially extending grooves are provided in the periphery of the portion 14 for the accommodation of axially spaced bearing rings 24 (preferably made of nylon 66 filled with molybdenum disulphide) and for the accommodation of axially spaced square section sealing rings 25 which are placed in back-to-back configuration in relation to one another. Said sealing rings may be so-called V-rings or lip seals but are in any case preferably made of an elastomeric material. The boss 20 is similarly formed with a circumferentially extending groove around its outer periphery for the accommodation of a square section sealing ring 30.

The air cylinder further comprises a stainless steel piston rod 31 whose axially inner end is bored and tapped at 32, the outside diameter of said rod being complementary to the inside diameter of the counterbore 23 into which said axially inner end is inserted. A cap screw 33 carrying an annular bonded seal 34 is caused to extend through the bore 22 in the portion 14 and is thereafter screwed into the tapped end of the piston rod 31 in order to fixedly secure the piston rod and the piston to one another, the seal 34 becoming compressed between the head of the cap screw and the portion 14 to provide a fluid-tight seal between the opposite sides or faces of the piston.

The piston rod 31 extends through the end cap 11 which is appropriately bored and counterbored to provide

a. a complete through-passage for the piston rod;

b. an annular seat for the accommodation of a bearing 40 which is preferably made of a synthetic resin material having a low coefficient of friction; and

c. an annular seat for an annular square section sealing ring 41.

It will be seen from FIG. 2 that boring and counterboring and the positioning of the square section sealing ring 41 are such that the eventual super-atmospheric fluid pressure within the air cylinder to the left of the piston 13 will cause that sealing ring 41 to seal against the piston rod 31 by virtue of the fact that said fluid pressure is free to reach said ring by way of a female recess 42 and an annular clearance 43.

The boss 44 of the end cap 11 is further provided with an internal groove for the accommodation of a wiper ring 50 and may be provided with an exterior screw-thread 51.

That end of the end cap 11 which is remote from the boss 44 is of reduced diameter such as will enable said end to be inserted into the respective end of the cylinder barrel 10, said reduced diameter end of said end cap being formed with a circumferential groove for the accommodation of a sealing O-ring 52. The O-ring 52 provides a fluid-tight seal between the end cap 11 and the respective end of the cylinder barrel 10.

The end cap 12 is similarly provided with a male boss 53 and a female recess 54, said boss having a circumferential groove formed therein for the accommodation therein of an annular square section sealing ring 60. That end of the end cap 12 which is adjacent the boss 53 is of reduced diameter such as will enable said end to be inserted into the cylinder barrel 10 and a circumferential groove is provided in said reduced diameter end for the accommodation therein of a sealing O-ring 61. Said O-ring 61 creates a fluid-tight seal between the end cap 12 and the respective end of the cylinder barrel 10.

Each of the end caps 11, 12 is bored to provide parallel passageways 70, 71 (see FIG. 3) within the thicknesses of the end caps, said passageways being open at both ends. At their upper ends (as seen in FIGS. 2 and 3) the passageways communicate with apertures 72, 73 respectively into which screw-threaded plugs can be screwed, as required, to blank off unwanted exhaust orifices. At their lower ends (as seen in said Figures) the passageways 70, 71 communicate with axially extending passages 74, 75, respectively, which are bored from the respective face of the end cap. Portions of said passages 74, 75 are of larger diameter than the other portions thereof, said portions of larger diameter being such as will accommodate the ends of conduits 80, 81. Each end of each conduit is provided with a sealing O-ring 82 which is located in a circumferential groove in said end and which is intended to make a fluid-tight seal between the end cap and the conduit. Furthermore, the conduit 80 interconnects the passageways 70 and 71 in the opposite end caps and the conduit 81 establishes the same interconnection between the remaining two passageways 70, 71 in said end caps.

A passageway 83, extending radially of each end cap, crosses and therefore communicates with the passageway 70. In the case of the end cap 11, the radially inner end of the passageway 83 communicates with the recess 42 and the clearance 43 and, in the case of the end cap 12, the radially inner end of said passageway 83 communicates with a female recess 84 which is bored in the boss 53. In the case of each end cap, the radially outer end of the passageway 83 extends through the end cap to provide an air-exhaust which is plugged with a conventional cushion adjusting screw and metering needle assembly indicated generally by the reference numeral 90, a fluid-tight seal being provided between the end cap and said assembly by an O-ring 91 for which a circumferential seat is provided in the assembly.

The two end caps 11, 12 are held in position in the respective ends of the cylinder barrel 10 by four tie rods 92 which extend axially of the air cylinder externally of the cylinder barrel 10 and through the opposed end caps, nuts 93 being threaded onto the screw-threaded ends of said tie rods and tightened up against said end caps.

The air cylinder described above may be mounted in any desired manner on the equipment to which the cylinder is fitted, for example by front or rear trunnion, base or nose mounting, front or rear end plate, and so on.

The air lines may be connected to the more accessible pair of the two pairs of ports 72, 73. Thus, assuming that the ports in the end cap 11 are labelled A and C and that the ports in the end cap 12 are labelled B and D, with the parts A and B in axial alignment with one another and with the ports C and D in axial alignment with one another, it will be possible to connect the air lines to the ports A and C and to blank off the ports B and D with screwed plugs, or to connect the air lines to the ports B and D and to blank off the unwanted ports A and C with screwed plugs. Moreover, it will be possible to connect said air lines to the ports B and C or A and D and to blank off the unwanted ports A and D or B and C, respectively, with said screwed plugs. The latter configuration of air lines connection (i.e. diagonally) is probably unlikely to be of any great significance from a practical point of view but the free choice of air cylinder end to which to connect the air lines could be of great practical significance in some locations.

Let it be assumed that the air lines and air line switching assembly has been connected to the end cap 12. Screwed plugs will have been inserted in the ports 72, 73 in the end cap 11. Air at super-atmospheric pressure supplied to the passageway 70 by way of the port 72 travel by way of the passageway 83 to the recess 84 and will thereby act upon the piston 13 to displace that piston and the piston rod 31 towards the left as seen in FIG. 2. Simultaneously, said air at super-atmospheric pressure will travel from the passageway 70 through the passage 74 and through the conduit 80 to the passage 75 and the passageway 71 in the end cap 11, but said air will not be able to escape to atmosphere because the port 73 in the end cap 11 will have been blanked off. The piston 13 will accomplish its stroke quite freely and at a speed which will be dependent upon, inter alia, the super-atmospheric pressure until the boss 20 enters the recess 42. Thereupon, the speed of travel of the piston will be progressively slowed, in known manner, by the cushioning effect provided by the air trapped between the leading end of the boss 20 and its sealing ring 30 and the recess 42 and its sealing ring 41, said air only being able to escape atmosphere at a rate which is determined by the adjustment of the cushion adjusting assembly 90.

When the supply of pressurised air to the right-hand side (as seen in FIG. 2) of the piston is discontinued and when the used air on said right-hand side of the piston is vented to atmosphere simultaneously with the supply of air at super-atmospheric pressure to the left-hand side of the piston 13, said piston will be displaced towards the right as seen in FIG. 2. Said pressurised air is supplied to the left-hand side of the piston 13 by way of the passageway 71 in the end cap 12, the passage 75, the conduit 81, the passage 74 in the end cap 11, the passageway 70 and the passageway 83 and the recess 42 in said end cap 11. The piston 13 is consequently displaced to the right and will move freely until such time as the recess 21 begins to move onto the boss 53, whereupon the cushioning effect is obtained once again.

Referring to FIG. 4, parts of the air cylinder illustrated therein which are identical to the corresponding parts described above with reference to FIGS. 1 to 3 are indicated by the same reference numerals, and detailed description of the entire air cylinder will not be repeated.

The air cylinder illustrated in FIG. 4 is essentially different from that illustrated in FIGS. 1 to 3 in that the piston rod 31 is tubular over at least the majority of its length in order to accommodate a portion or substantially the whole of a location rod 100 whose section must be non-circular and is (in the embodiment illustrated) square. The piston 13 and the axially inner end of the piston rod 31 are secured to a bearing 101 made of a material having a low coefficient of friction. Indeed the bearing 101, the axially inner end of said piston rod 31 and the piston 13 are not simply connected to one another by opposed set screws 102 but their mutually contacting surfaces are also cemented to one another (as for example by a single component cyanoacrylate adhesive or an adhesive based on oxygenated methacrylic molecules). It will be appreciated that the cross-section of the bore of the annular bearing 101 must be complementary to the section of the location rod 100.

The right-hand end (as seen in FIG. 4) of the location rod 100 is cemented to a plug 103 which is itself cemented inside the recess 84 in the bos 53, and the plug 103 is further connected to said boss 53 by a cross-pin 104 which extends through said plug and said end of the location rod and which is also cemented thereto.

Referring to FIG. 5, there is illustrated an end cap 110 similar to the end cap 11 which is illustrated in FIGS. 1 to 4, the cylinder barrel 10 and the piston rod 31 of the air cylinder having been drawn in chain dotted lines. Said end cap 110 houses a captive axially movable plunger 111 whose right-hand end constitutes a nose projecting inwardly of the end cap 110 towards the piston and which has a mid-length portion 112 of reduced diameter, the length of said portion 112 being defined by two opposed frusto-conical portions 113, 114 which are intended to act as cams. Extending from the frusto-conical portion 113 to a nose 120 is a second portion 121 of reduced diameter and a compression spring 122 has its convolutions concentric with said portion 121 and is confined between two circlips 123, 124 which are slidable along said portion 121 in the circumstances hereinafter described. A screw-threaded annular plug 130 is screwed into and cemented in a tapped hole formed in the end cap 110 to provide an abutment for the left-hand end of the spring 122 as seen in FIG. 5, the nose 120 extending through said plug, the right-hand end of said spring being held against axially inwards movement by the circlip 124 abutting against a shoulder 131 of the end cap 110. A circumferential groove in the plunger 111 accommodates a sealing O-ring 132 which provides a fluid-tight seal between the end cap 110 and said plunger.

Two balls 133, 134 are (in the rest condition of the mechanism) in contact with the plunger 111 at the junctions between the frusto-conical portions 113, 114 and the portion 112, and two microswitch plungers 140, 141 are accommodated in appropriate radial bores in the end cap 110 and have their radially inner end faces in contact with the balls 133, 134. The radially outer end faces of said plungers 140, 141 are adjacent the switch elements of a microswitch which is indicated generally by the reference numeral 142 but which will not be further described except to say that said microswitch is connectible to means (not illustrated) operable to indicate the condition of the air cylinder. Said means could be for example coloured lights or an audible signal means.

An adjustable collar 143 is connected to the piston rod 31 by a set screw 144.

When the piston of the air cylinder nears the end of its stroke towards the end cap 110, a part of the face of said piston will contact the projecting nose of the plunger 111 within the cylinder barrel and will, during completion of its stroke, move said plunger 111 towards the left and will compress the spring 122. This will result in the ball 134 being cammed radially outwardly of the end cap, whereby the microswitch plunger 141 will actuate the appropriate part of the microswitch. When the piston moves away from the end cap 110, the compression spring 122 moves the plunger 111 towards the right and the operated part of the microswitch 142 reverts to its previous unoperated condition. Continued movement of the piston away from the end cap 110 of the air cylinder to the other end cap thereof (not illustrated) will eventually cause the leading surface of the collar 143 to be brought into contact with the nose 120 of the plunger 111. In the course of completing its stroke, said piston will cause the plunger 111 to be moved to the right thereby compressing the spring 122 and camming the ball 133 and the plunger 140 upwardly to actuate the other part of the microswitch.

One advantage which stems from the provision of two sets of ports in the end caps is that a solenoid valve can be fitted at whichever end of the air cylinder is most convenient; in particular, it would be desirable for certain applications to use the solenoid valve assembly, complete with speed control, described and illustrated in U.S. Pat. application Ser. No. 47,666, filed June 19, 1970, now U.S. Pat. No. 3,688,799. Furthermore, the collar 143 can be used in conjunction with the microswitch 142 and said solenoid valve assembly to limit the stroke of the piston.

Claims

What we claim as our invention and desire to secure by letters patent of the United States is:

1. A cushioned air cylinder of tie-rod construction, comprising an opened ended cylinder barrel, a pair of end caps closing the ends of said barrel in a fluid-tight manner, means in said end caps for admitting air under super-atmospheric pressure to the barrel and for exhausting air therefrom, each end cap being provided with a pair of ports forming part of said means for admitting and exhausting air and which may be selectively blanked off by inserting screw plugs, said means further including first and second duct means in one end cap and third and fourth duct means in the other end cap, said first and third duct means communicating one of said ports in the respective end cap with the adjacent end of the cylinder barrel and said second and fourth duct means communicating the other of said ports in the respective end cap with the opposite end of the cylinder barrel by way of a conduit extending externally of said barrel between said end caps, a piston disposed within the barrel for reciprocating movements therealong under the influence of air under super-atmospheric pressure, a piston rod extending through one of said end caps and having its inner end fixedly secured to said piston, said piston having axially aligned male and female portions of which the male portion carries an annular seal, one of said end caps being provided with a female cushion bore and the other end cap being provided with a male boss carrying an annular seal, said bore and boss of said end caps interfitting with the male and female portions of the piston respectively and thereby providing plug-seal cushioning effect during operation of the cylinder.

2. A cushioned air cylinder as claimed in claim 1, wherein said inner end of the piston rod extends into the piston over an axial distance which is at least substantially equal to the axial length of said male portion of the piston.

3. A cushioned air cylinder as claimed in claim 1, wherein each end cap is provided with cushion adjusting screws and is also appropriately formed to provide bleed passages therethrough for the air being "compressed" by movement of the piston.

4. A cushioned air cylinder as claimed in claim 1, wherein a passageway extends through said piston, a location rod having a free part extends through said passageway and said piston is slidable along said rod in carrying out said reciprocating movements, the cross-sectional shape of at least a portion of said passageway and that of said location rod being complementary to one another and non-circular.

5. A cushioned air cylinder as claimed in claim 4, wherein the said piston rod is hollow and wherein the longitudinal axes of the location rod and the piston rod are coincident, at least a part of the length of said location rod being accommodated at all times within the piston rod.

6. A cushioned air cylinder as claimed in claim 5, wherein said piston rod is able to accommodate the whole of the free part of the location rod during said reciprocating movements of the piston.

7. A cushioned air cylinder as claimed in claim 4, wherein one end of the location rod is fixedly secured to that end cap of the air cylinder through which the piston rod does not extend and wherein the piston includes a bearing made of a material having a low coefficient of friction, said bearing being fixedly secured to the piston to form part of the piston and having said passageway of non-circular section formed therethrough.

8. A cushioned air cylinder as claimed in claim 7, wherein each of said passageway and said location rod is of square cross section.