Pneumatic cylinder with cushioning means disposed in an end cover

Abstract

 A pneumatic cylinder comprising a cylinder tube (1) with end covers (2), a piston (3) sliding within the cylinder tube (1),

• at least one piston packing ring (4) disposed on the outer peripheral surface of the piston (3) for defining at least one pressure chamber (7), and
• at least one outer port (8) for supplying and discharging compressed air to and from said pressure chamber (7) separated by the piston (3),
• a respective air outlet (6) positioned with an axial cushioning distance (X) to the end of the cylinder tube (1) for connecting the pressure chamber (7) with the corresponding outer port (8) via a wall channel () at least partly arranged along in the cylinder tube (1), whereby
• at least one end cover channel (10) with an integrated cushioning nozzle (9) is arranged in the end cover (2) for connecting the pressure chamber (7) with the corresponding outer port (8) in order to discharge compressed air within the pressure chamber (7) only through the cushioning nozzle (9) when the piston packing ring (4) passes over the air outlet (6) on the discharge side just before the piston (3) reaches the end of its stroke during the discharge cycle, wherein
• a check valve (11) is inserted in the wall channel (12) for stopping air flow to the air outlet (6) during the supply cycle of the corresponding pressure chamber (7).

Description

[0001] The present invention relates to a pneumatic cylinder comprising a cylinder tube with end covers, a piston sliding within the cylinder tube, at least one piston packing ring disposed on the outer peripheral surface of the piston for defining at least one pressure chamber, and at least one outer port for supplying and discharging compressed air to and from said pressure chamber separated by the piston, a respective air outlet positioned with an axial cushioning distance (X) to the end of the cylinder tube for connecting the pressure chamber with the LK: corresponding outer port via a wall channel, at least partly arranged along the cylinder tube. Moreover, the present invention relates to a rodless linear unit comprising a pneumatic cylinder of that kind.

[0002] The GB 2 347 176 shows a pneumatic cylinder with end cushioning means. The end cushioning means are completely integrated into the wall section of the cylinder tube and comprise discharge outlets and check valves. In order to move the inner piston compressed air initially enters the pressure chamber via an outer port through a bypass channel, a check valve and a first bore. As piston moves further a piston ring uncovers a second bore, so allowing unrestricted air flow from said port to the pressure chamber. Once piston reaches a cushioning distance from the end of its stroke a piston ring covers and blocks one of two outlet bores, so forcing air to discharge to the respective outer port via a check valve with throttling means and a bypass channel. Thus, the restricted outflow serves to decelerate the piston. In fact this construction allows a short cylinder design but a thick-walled cylinder tube is needed for placing the cushioning means.

[0003] The DE 101 45 811 A1 discloses a further pneumatic cylinder of the kind interesting in connection with the present invention. The end cushioning means are also completely integrated into the wall section of the cylinder tube. Altogether three openings to each inner chamber are necessary for supplying and cushioning the piston movement. The middle opening is equipped with an adjusting screw which is screwed in the wall section of the cylinder in order to set the cushioning speed. A thick-walled cylinder tube is needed for placing the cushioning means. Furthermore, the adjusting screw needs space in the axial direction of the cylinder tube because it has to be placed between the end cover and the outer port.

[0004] It is an object of the present invention to provide a pneumatic cylinder with a thin-walled cylinder design comprising bypass channel cushioning means of the above-mentioned kind which are suitable for long cushioning lengths.

[0005] This object is achieved with a pneumatic cylinder comprising the features as set forth in the characterizing portion of Claim 1.

[0006] The cushioning means of the present invention comprise at least one end cover channel with an integrated cushioning nozzle which is arranged in the end cover for connecting the pressure chamber with the corresponding outer port in order to discharge compressed air within the pressure chamber only through the cushioning nozzle when the piston packing ring of the piston passes over the air outlet on the discharge side just before the piston reaches the end of its stroke during the discharge cycle, wherein a check valve is integrated in the wall channel for stopping air flow to the air outlet during the supply cycle of the corresponding pressure chamber.

[0007] In the range of the invention it is also possible that the end cover channel itself comprises the function of the cushioning nozzle. It means that a separate cushioning nozzle part is not needed. Since most of the cushioning means are integrated in the end cover the pneumatic cylinder according to the present invention does not need a thick-walled cylinder tube, which enables the air cylinder to be miniaturized. Moreover, the cushioning length only depends from the length of the wall channel of the cylinder tube. Thus, long cushioning lengths are possible. Since during the supply cycle no compressed air flows through the wall channel, there is no need for a special piston design with a special piston packing ring arrangement.

[0008] In order to save space the check valve of the wall channel should be disposed in a section of the wall channel which runs through the end cover. A suitable check valve for inserting in the wall channel comprises a ball element which is pressed against a valve seat by means of a compression spring.

[0009] In a preferred embodiment a further check valve is arranged in a further end cover channel which runs parallel to the first end cover channel. This arrangement allows to speed up the piston during the supply cycle, because compressed air flows through the cushioning nozzle and through the further parallel end cover channel to the pressure chamber.

[0010] In a specific embodiment the wall channel is directly integrated into the wall section of the cylinder tube. It is also possible to use a separate conduit running along the outer surface of the cylinder tube.

[0011] Preferably, the pneumatic cylinder according to the present invention is suitable for rodless linear units with a slide table.

[0012] The invention will now be further described by way of an example with reference to the accompanying drawings in which:

Fig. 1

is a side-sectional view of the right part of a pneumatic rodless linear unit, and

Fig. 2

is a side-sectional view of a detail of Fig. 1 showing the cushioning means.

[0013] The rodless linear unit according Fig. 1 comprises a cylinder tube 1, both ends thereof being closed by end covers 2 (only one of them is shown), a piston 3 which reciprocates within the cylinder tube 1 sliding air-tightly by means of a piston packing ring 4, and a slide table 5 connected to the piston 3.

[0014] As shown in Fig. 2 in the vicinities of ends of the cylinder tube 1, an air outlet 6 for supplying and discharging compressed air are disposed, respectively, with an axial cushioning distance X. Each air outlet 6 communicate with a corresponding pressure chamber 7, defined at both sides of the piston 3, via outer ports 8 respectively. The piston 3 is driven to be reciprocated in the cylinder tube 1 by supplying and discharging compressed air to/from the pressure chambers 7 from/to the ports 8 via the air outlets 6.

[0015] Furthermore, end cushioning means are provided for stopping the piston 3 in a cushioning manner by restraining the flow of discharged air from the pressure chambers 7. The cushioning means comprise - referring to one side of the pneumatic cylinder only - a cushioning nozzle 9 integrated in an end cover channel 10, which is connected to the outer port 8.

[0016] The discharged air within the pressure chamber 7 of the pneumatic cylinder runs only through the cushioning nozzle 9 when a piston 3 passes over the air outlet 6 on the discharge side just before the piston 3 reaches the right end of its stroke, wherein only the end cover channel 10 connects the pressure chamber 7 with the outer port 8. The end of the piston stroke is defined by the corresponding surface of the end cover 2.

[0017] Furthermore, a check valve 11 is inserted in a wall channel 12 for stopping air flow to the air outlet 6 during the supply cycle of the corresponding pressure chamber 7. The wall channel 12 is integrated into the wall section of the cylinder tube 1. The check valve 11 is disposed in a section of the wall channel 12 which runs through the end cover 2. A further check valve 13 is arranged in a further end cover channel 14 which runs parallel to the first end cover channel 10 in order to speed up the piston 3 during the supply cycle when supplying compressed air to the pressure chamber 7. Both check valves 11 and 13 comprise a ball element 15 which is pressed against a valve seat 16 by means of a compression spring 17.

[0018] By cushioning means according to the present invention long cushioning lengths are possible, especially for rodless cylinders with a thin-walled cylinder design.

[0019] The present invention is not limited to rodless linear units as described above but it is also provided for all kind of pneumatic cylinders.

Reference Signs

[0020] 

1

cylinder tube

2

end cover

3

piston

4

piston packing ring

5

slide table

6

air outlet

7

pressure chamber

8

outer port

9

cushioning nozzle

10

end cover channel

11

check valve

12

wall channel

13

check valve

14

end cover channel

Claims

1. A pneumatic cylinder comprising a cylinder tube (1) with end covers (2), a piston (3) sliding within the cylinder tube (1),

- at least one piston packing ring (4) disposed on the outer peripheral surface of the piston (3) for defining at least one pressure chamber (7), and

- at least one outer port (8) for supplying and discharging compressed air to and from said pressure chamber (7) separated by the piston (3),

- a respective air outlet (6) positioned with an axial cushioning distance (X) to the end of the cylinder tube (1) for connecting the pressure chamber (7) with the corresponding outer port (8) via a wall channel () at least partly arranged along in the cylinder tube (1),

characterized in that

- at least one end cover channel (10) with an integrated cushioning nozzle (9) is arranged in the end cover (2) for connecting the pressure chamber (7) with the corresponding outer port (8) in order to discharge compressed air within the pressure chamber (7) only through the cushioning nozzle (9) when the piston packing ring (4) passes over the air outlet (6) on the discharge side just before the piston (3) reaches the end of its stroke during the discharge cycle, wherein

- a check valve (11) is inserted in the wall channel (12) for stopping air flow to the air outlet (6) during the supply cycle of the corresponding pressure chamber (7).

2. A pneumatic cylinder according to claim 1,
characterized in that the check valve (11) is disposed in a section of the wall channel (12) which runs through the end cover (2).

3. A pneumatic cylinder according to claim 1 or 2,
characterized in that a further check valve (13) is arranged in a further end cover channel (14) which runs parallel to the first end cover channel (10) in order to speed up the piston (3) during the supply cycle when supplying compressed air to the pressure chamber (7).

4. A pneumatic cylinder according to one of the preceding claims,
characterized in that the check valve (11; 13) comprise a ball element (15) which is pressed against a valve seat (16) by means of a compression spring (17).

5. A pneumatic cylinder according to one of the preceding claims,
characterized in that the outer port (8) for supplying and discharging compressed air to and from said pressure chamber (7) is arranged on the end cover (2).

6. A pneumatic cylinder according to one of the preceding claims,
characterized in that the wall channel (12) is integrated into the wall section of the cylinder tube (1).

7. A rodless linear unit with a slide table (5) comprising a pneumatic cylinder according to at least one of the preceding claims.

Drawing