US3303756A

US3303756A - Pneumatic cylinders

Info

Publication number: US3303756A
Application number: US416052A
Authority: US
Inventors: Geeson Robert Ernest
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1963-12-04
Filing date: 1964-12-04
Publication date: 1967-02-14
Anticipated expiration: 1984-02-14
Also published as: GB1019988A

Description

Feb. 14, 1967 R. E. GEEsoN 3,303,756

PNEUMATIC CYLINDERS I Filed Dec. 4, 1964 3 Sheets-Sheet 1 EH Lk T v Q5 nvenlor 2705er? ErfLeJZ 'ee'aru.

Feb- 14, 1957 R. E. GEEsoN PNEUMATIC CYLINDERS 5 Sheets-Sheet 2 Filed Dec. 4, 1964 n venlor OZ er? Em esi 02295071/ Feb. 14, 1967 R, E. GEL-:SON

PNEUMATIC CYLINDERS 3 Sheets-Sheet 3 Filed DSG. 4, 1964 Inventor I@ 27er? Erfzf 6565070.

By aj/m, ff-L, wmf/@1% United States Patent 3,303,756 PNEUMATIC CYLINDERS Robert Ernest Geeson, Croydon, England, assigner to The Metal Box Company Limited, London, England, a British company Filed Dec. 4, 1964, Ser. No. 416,052 Claims priority, application Great Britain, Dec. 4, 1963, 47,966/ 63 11 Claims. (Cl. 92--85) This invention relates to pneumatic cylinders.

As is well understood a mechanism operated by a pneumatic cylinder can sometimes be arranged to limit the travel of the operating piston at each end of the stroke thereof and this is sometimes effected by permitting metallic contact with the cylinder end covers. This, however, results in an undesirable volume of noise and shock loads on the components of the cylinder and the mechanism operated thereby and such loads are conducive of fatigue failures.

It is also known that a desirable cushioning effect can be provided for long-stroke cylinders by using truncated pistons with projecting portions on both sides of the main portion of the piston, such projecting portions having diameters substantially smaller than that of said main portion. These projecting portions are arranged to enter cavities in the cylinder end covers prior to the main portion of the piston reaching the end of its stroke. Air thus entrapped in such cavities becomes pressurised to a degree suflicient to cause the piston travel to be retarded smoothly to rest. A controlled release of pressure from the cavities is usually provided to ensure that completion of the stroke is effected.

When the pneumatic cylinder is a short-stroke cylinder, particularly a cylinder having a working stroke which is shorter than the internal diameter of the cylinder, it is not possible to use the cushioning methods which can be used with long-stroke cylinders and it is an object of the present invention to provide a short-stroke pneumatic cylinder with adequate cushioning means.

According to the invention there is provided a pneumatic cylinder comprising an operating piston movable axially in a housing in response to air pressure admitted to the housing and having a stroke the length of which is less than the internal diameter of the housing, a piston rod movable axially with the operating piston and arranged for connection with a member to be operated thereby, and a cushioning device external of said housing and comprising a cushioning piston movable axially in a cushioning chamber in response to movement of the operating piston, said cushioning chamber being provided at each of the opposite ends thereof with a shallow recess into which the cushioning piston is moved at it approaches an end of the stroke thereof thereby to cornpress air in the recess to retard and arrest movement of the operating piston before it engages the end of the housing, and openings in the side of the cushioning chamber to maintain at atmospheric pressure that portion of the cushioning chamber which is behind the cushioning piston as it enters one of the shallow recesses. The diameter of the cushioning piston is preferably substantially equal to or is greater than that of the operating piston.

The diameter of the cushioning piston may be slightly less than the internal diameter of said recess thereby to permit air entrapped as the cushioning piston approaches the end of a recess to escape slowly around the cushioning piston while permitting the cushioning piston to reacn the full extent of the stroke thereof.

In one embodiment of the invention the cushioning chamber is formed by a body portion and a co-axial chamber cover retained in spaced axial relation by a sleeve tted over spigots extending respectively from the body portion and the chamber cover, said sleeve having an internal wall which is interrupted between the ends of the sleeve to provide at the ends thereof continuous wall portions which extend from the end faces of said spigots and dene the axial length of the shallow recesses. The interruption may be formed by ports extending radially through the sides of the sleeve. Alternatively, the interruption may be formed by an annular groove formed in the sleeve and ports which extend from the groove to the exterior of the sleeve.

In another embodiment of the invention the cushioning chamber is formed by a body portion and a co-axial chamber cover located in spaced axial relation by a sleeve co-axial with and rotatable about the axis of the chamber and provided with left and right hand internal screw threads spaced apart axially of the sleeve, said body portion and chamber cover having spigots of lesser external diameter than the internal diameter of the sleeve and the end faces of which are directed towards each other to form the opposite ends of the cushioning chamber, and left and right hand rings slidable axially in the annular spaces formed between the sleeve and spigots and provided respectively with left and right hand external screw threads which mesh with the like internal threads provided on the sleeve, the inner walls of the rings extending beyond the end faces of the spigots to form said recesses therewith, the axial length of the recesses being adjustable by rotation of the sleeve and atmospheric air admissible to the cushioning chamber through radial ports formed in the sleeve between the position of location of said internal screw threads.

The housing may be formed by a cylinder one end of which is screwed into said body portion of the cushioning chamber on the side thereof opposite that `on which the spigot is formed, and the opposite end of the cylinder is screwed into a housing end cover, and the operating and cushioning pistons are arranged each to be movable axially with the piston rod. The cushioning piston may be integral with a sleeve co-axial with and connected to the piston rod and the cushioning piston be guided for axial movement by a projection co-axial therewith and extending from the chamber cover.

In order that the invention may be clearly understood some embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a longitudinal section through a pneumatic cylinder according to the invention,

FIGURE 2 is a view of a part of FIGURE 1 showing a modification thereto,

FIGURE 3 is a longitudinal section through an alternative form of pneumatic cylinder according to the invention,

FIGURE 4 is a section of a part of a pneumatic cylinder and illustrates an alternative form of cushioning chamber which can be employed therewith, and

FIGURE 5 is a longitudinal section through another alternative form of pneumatic cylinder according to the invention.

In the drawings like or similar parts are indicated by like reference numerals.

Referring to FIGURE l, the pneumatic cylinder comprises an operating piston 1, of known construction, movable axially in a housing 2 in response to air pressure admitted to the housing through

ports

3, 4 according to the direction of movement of the piston. The piston 1 has a stroke the length of which is less than the intern-al diameter of the housing 2. A piston rod 5 is movable axially with the operating piston 1 and is arranged for c-onnection, `as by a screw threaded end 6, with a member 7 Ito be operated thereby. As shown in the drawings, the housing is formed by a cylinder 8 and one end 3 9 of which is screwed into the body portion 10 of a cushioning chamber, to be described below, an-d the opposite end 11 of cylinder 8 is screwed into a housing end cover 12.

External of the housing 2 there is provided a cushioning device comprising a cushioning piston 13 movable axially in a cushioning chamber 14 in response to movement of the operating piston 1. The cushioning chamber is provided at each of the opposite ends thereof with a shallow recess 15 into which the cushioning piston 13 is moved as it approaches an end of the stroke thereof thereby to compress air in the recess to retard and arrest movement of the operating piston 1 before it engages the end of the housing 2. Openings, shown as ports 16, in the side of the cushioning chamber 14 maintain at atmospheric pressure that portion of the cushioning chamber which is behind the cushioning pist-on 13 as it enters one of the shallow recesses 15. The diameter of the cushioning piston 13 is substantially eq-ual to or is greater than that of the -operating piston 1 and the arrangement is such that the whole of the area of a face of the cushioning piston 13 can come into close contact with the ends of the recesses 15 at the ends of the stroke of the cushioning piston.

The diameter of the cushioning piston 13 is slightly less than the internal diameter of the recesses 15 so as to permit air entrapped as the cushioning piston approaches the end of a recess to escape slowly around the cushioning piston while permitting the cushioning pist-on to reach the full extent of the stroke thereof. In the embodiment of the invention illustrated in FIGURE 1 the piston rod is a close sliding t in

bearings

17, 18 and the diameter of the cushioning piston 13 is such that it will not usually be tit-ted with sealing devices.

The cushioning chamber 14 is formed by the `body portion and a co-axial chamber cover 19 retained in spaced axial relation by a sleeve 20 titted over

spigots

21, 22 extending respectively lfrom the body portion 10 and the chamber cover 19 an-d the sleeve 20 has an internal wall which is interrupted between the ends of the sleeve to provide at the ends thereof continuous Wall portions 23 which extend from the end faces of the spigots 21, 212 and define the axial length of the shallow recesses 15. As shown in FIGURsE 1 the interruption is formed by the ports 16 which ex-tend radially through the sides of the sleeve but in the modified embodiment of the invention shown in FIGURE 2 the interruption is formed by an annular groove 24 and ports 16a extend from the groove 24 t-o the exterior of the sleeve.

`In the alternative form of pneumatic cylinder shown in FIGURE 3 the cushioning piston 1-3 is integral with a sleeve 215 co-axial with and connected to the piston rod `5 and the cushioning piston is guided for axial movement by a projection 26 co-axial therewith and extending from the chamber cover 19.

FIGUR'E 4 illustrates a modified form of cushioning chamber in which a sleeve 20a locates the body portion 10 and chamber cover 19 in axial spaced relation. The sleeve 20a is rotatable about the axis of the cushioning chamber and is provided with left and right hand

internal screw threads

27, 28 spaced apart axially of the sleeve. The end cover is retained in position by bolts 29 extending through distance pieces 30 and the sleeve 20a is normally restrained against rotation by a clamping member 31. The body portion 10 and chamber cover 19 respectively Ihave spigots 32, 33 of lesser external diameter than the internal diameter of the sleeve 20a and the end faces of the spigots are directed towards each other to for-m the opposite ends of the cushioning chamber. Left and

right hand rings

34, 35 are slidable axially in Ithe annular spaces formed between the sleeve 20a and

spigots

32, 33 and are provided respectively with left and right hand external screw threads which mesh with the ylike inte-rnal threads provided on the sleeve 20a. The inner walls of the

rings

34, 35 extend beyond the end faces of the

spigots

32, 33 to form therewith recesses 15. By releasing the clamping member 31 the sleeve 20a can be rotated and thus affect adjustment of the axial length of the recesses 15 by effecting axial movement of the rings simultaneously in opposite directions. In this ernbodiment of the invention atmospheric air is admissible to the cushioning chamber through ports 16b formed in the sleeve 20a between the positions of locations of the internal screw threads 27, Z8.

In each of the embodiments of the invention the cushioning chamber 14 is provided with

ports

16, 16a or 16b so that when the cushioning piston 13 is in close contact with an end ofthe cham-ber atmospheric air is allowed to enter the chamber at the opposite side of the piston. The dimensions of the ports are so proportioned in respect of the working pressure of the operating cylinder an-d the mass of the -moving parts that shortly before each end of the stroke la volume of atmospheric air is entrapped by the cushioning piston 13 in a recess 15. This volume of air is selected to be suflicient to retard movement of the operating piston 1 so that the mechanism is arrested without violent impact, the clearance around the piston enabling the entrapped air to escape slowly enough to achieve this object without preventing the cushioning piston from reaching the full extent of its stroke.

As described above the cushioning chamber 14 is integral with, but external of, the housing 2 but if desired the cushioning chamber 19 may be separate from the housing 2 as shown in FIGURE 5. When the chamber 14 is integral with the housing 2 the pistons 1 and 13 are conveniently both movable with the piston rod 5 but if the chamber 14 is separate from housing 2 a piston rod for the piston 13 may be attached to the piston rod for piston 1 or to some convenient part of the member 7 operated by the piston 1 as shown in FIGURE 5.

I claim:

1. A pneumatic cylinder comprising an operating piston movable axially in a housing in response to air pressure admitted to the housing and having a stroke the length of which is less than the internal diameter of the housing, a piston rod movable axially with the operating piston and arranged for connection with a member to be operated thereby, and a cushioning device external of said housing and comprising a cushioning piston movable axially in a cushioning chamber in response to movement of the operating piston, said cushioning chamber being provided at each of the opposite ends thereof with a shallow recess into which the cushioning piston is moved as'it approaches an end of the stroke thereof thereby to compress air in the recess to retard and arrest movement of the operating piston before it engages the end of the housing, and openings in theside of the cushioning chamber to maint-ain at atmospheric pressure that portion of the cushioning chamber which is behind the cushioning piston as it enters one of the shallow recesses.

2. A pneumatic cylinder according to claim 1, wherein the diameter of the cushioning piston is substantially equal to or is greater than that ofthe operating piston.

3. A pneumatic cylinder according to claim 1, wherein the diameter of the cushioning piston is slightly less than the internal diameter of said recesses thereby to permit air entrapped as the cushioning piston approaches the end of a recess to escape slowly around the cushioning piston while permitting the cushioning piston to reach the full extent of the stroke thereof.

4. A pneumatic cylinder according to claim 1, wherein the cushioning -chamber is formed by .a body portion and a co-axial chamber cover retained in spaced axial relation by a sleeve iitted over spigots extending respectively from the body portion and the chamber cover, said sleeve having an internal wall which is interrupted between the ends of the sleeve to provide at the ends thereof continuous wall portions which extend from the end faces of the said spigots and define the axial length of the shallow recesses.

5. A pneumatic cylinder according to claim 4, wherein the interruption is formed by ports extending radially through the sides of the sleeve.

6. A pneumatic cylinder according to claim 4, wherein the interruption is formed by an annular groove formed in the sleeve and ports extend from the groove to the exterior of the sleeve.

7. A pneumatic cylinder according to claim 1, wherein the cushioning chamber is formed by a body portion and a co-axial chamber cover located in spaced axial relation by a sleeve co-axial with and rotatable yabout the axis of the chamber and provided with left and right hand internal screw threads spaced apart axially of the sleeve, said body portion and chamber cover having spigots of lesser external diameter than the internal diameter of the sleeve and the end faces of which are directed towards each other to form the opposite ends of the cushioning chamber, and left and right hand rings slidable axially in the annular spaces formed between the sleeve and spigots and provided respec-tively with left and right hand external screw threads which mesh with the like internal threads provided on the sleeve, the inner walls ofthe rings extending beyond the end faces of the spigots to form said recesses therewith, the axial length of the recesses being adjustable by rotation of the sleeve and atmospheric air admissible to the cushioning chamber through radial ports formed in the sleeve between the positions of location of said internal screw threads.

8. A pneumatic cylinder according to claim 7, wherein the housing is formed by a cylinder one end of which is screwed into said body portion of the cushioning chamber on the side thereof opposite that on which the spigot is formed, and the opposite end of the cylinder is screwed into .a housing end cover, and wherein the operating and cushioning pistons are each movable axially with the piston rod.

9. A pneumatic cylinder according to claim 7, wherein the cushioning pist-on is integral with a sleeve co-axial with and connected to the piston rod and the cushioning piston is guided for axial movement by a projection coaxial therewith yand extending from the chamber cover.

10. A pneumatic cylinder according to claim 4, wherein the housing is formed by a cylinder, one end of which is screwed into said body portion of the cushioning chamber on the side thereof opposite that on which the spigot is formed, and the opposite end of the cylinder is screwed into a housing end cover, and wherein the operating and cushioning pistons are each movable -axially with the piston rod.

11. A pneumatic cylinder .according to claim 4 wherein the cushioning piston is integral with a sleeve coaxial with and connected to the piston rod and the cushioning piston is guided for axial movement by a projection coaxial therewith and extending from the chamber cover.

References Cited by the Examiner UNITED STATES PATENTS 364,081 5/1887 Bates 92-85 X 859,629 7/1907 Symons et al 92-85 X 1,077,781 11/1913 Yeager 18S-88.1 1,522,243 1/1925 Hughes 18S-88.1 2,815,004 12/1957 Droman 92-85 FOREIGN PATENTS 1,267,211 6/ 1961 France.

MARTIN P. SCHWADRON, Primary Examiner.

I. C. COHEN, Assistant Examiner.

Claims

1. A PNEUMATIC CYLINDER COMPRISING AN OPERATING PISTON MOVABLE AXIALLY IN A HOUSING IN RESPONSE TO AIR PRESSURE ADMITTED TO THE HOUSING AND HAVING A STROKE THE LENGTH OF WHICH IS LESS THAN THE INTERNAL DIAMETER OF THE HOUSING, A PISTON ROD MOVABLE AXIALLY WITH THE OPERATING PISTON AND ARRANGED FOR CONNECTION WITH A MEMBER TO BE OPERATED THEREBY, AND A CUSHIONING DEVICE EXTERNAL OF SAID HOUSING AND COMPRISING A CUSHIONING PISTON MOVABLE AXIALLY IN A CUSHIONING CHAMBER IN RESPONSE TO MOVEMENT OF THE OPERATING PISTON, SAID CUSHIONING CHAMBER BEING PROVIDED AT EACH OF THE OPPOSITE ENDS THEREOF WITH A SHALLOW RECESS INTO WHICH THE CUSHIONING PISTON IS MOVED AS IT APPROACHES AN END OF THE STROKE THEREOF THEREBY TO COMPRESS AIR IN THE RECESS TO RETARD AND ARREST MOVEMENT OF THE OPERATING PISTON BEFORE IT ENGAGES THE END OF THE HOUSING, AND OPENINGS IN THE SIDE OF THE CUSHIONING CHAMBER TO MAINTAIN AT ATMOSPHERIC PRESSURE THAT PORTION OF THE CUSHIONING CHAMBER WHICH IS BEHIND THE CUSHIONING PISTON AS IT ENTERS ONE OF THE SHALLOW RECESSES.