Pneumatic cylinder

Abstract

The invention relates to a pneumatic cylinder (1) for providing linear motion, with a cylinder housing (2) in which a working recess (18) is formed in which a working piston (10) is linearly movable along an axis of motion (6), wherein the working piston (10) is connected to a piston rod (7; 57; 67) which passes through an end cover (4) arranged at the end of the cylinder housing (2), which has a piston rod seal (12) which seals against a sealing surface (26) of the piston rod (7; 57; 67). According to the invention, the piston rod (7; 57; 67) has a base body (8) designed as a threaded rod and an external thread (11) of the base body (8) is provided at least partially with a covering (9; 59; 69) from the group: coating, sleeve, which covers the external thread (11) and serves as a sealing surface (26) for the piston rod seal (12).

Description

[0001] The invention relates to a pneumatic cylinder for providing a linear movement, comprising a cylinder housing in which a working recess is formed, in which a working piston is accommodated so as to be linearly movable along a movement axis, wherein the working piston is connected to a piston rod which passes through an end cover arranged on the end of the cylinder housing, which cover has a piston rod seal which bears sealingly against a sealing surface of the piston rod.

[0002] The object of the invention is to provide a pneumatic cylinder that can be manufactured cost-effectively.

[0003] This task is solved for a pneumatic cylinder of the type mentioned above in that the piston rod has a base body designed as a threaded rod and an external thread of the base body is provided, at least in part, with a covering from the group: coating, sleeve, which covers the external thread and serves as a sealing surface for the piston rod seal. Through this design of the piston rod, the various functions that the piston rod must fulfill are each fulfilled by cost-effective components optimized for the respective purpose. The basic function of the piston rod is to transmit a force acting on the working piston, which is caused by pressurizing a working chamber delimited by the working piston and the working recess, to a component arranged outside the cylinder housing.This component could, for example, be a moving part of a device that can be driven by the pneumatic cylinder. Another basic function of the piston rod is to guide the working piston within the working recess to prevent tilting of the working piston, which can occur when compressive forces act on the working piston. For this purpose, the piston rod is mounted for linear movement in the end cover located at the end of the cylinder housing. In order to fulfill these basic functions, the piston rod must be sufficiently stable to be able to transmit the forces that can occur during proper use of the pneumatic cylinder. These basic functions are realized by the threaded rod.Furthermore, the threaded rod has the task of enabling the working piston to be coupled and of providing an interface for connecting to the component arranged outside the cylinder housing, for example the moving part of a device. Since the threaded rod is provided with a thread, preferably over its entire length, these tasks can be fulfilled without additional manufacturing effort. Furthermore, it is advantageous for single-acting pneumatic cylinders and essential for double-acting pneumatic cylinders that the piston rod, despite its relative linear mobility, also ensures a sealing function together with the piston rod seal provided in the end cover against the end cover arranged on the cylinder housing.Since this is not possible with the thread of the threaded rod, the sealing effect is achieved by means of a sleeve, at least for that area of ​​the piston rod along the travel path that the piston rod can perform relative to the cylinder housing. This sleeve has an outer surface that is sufficiently smooth to ensure the sealing effect required for the function of the pneumatic cylinder against the piston rod seal. This sleeve can be designed either as a coating made of a formless mass that is applied to the threaded rod, or as a sleeve that is pushed onto the threaded rod and secured there.Preferably, it is provided that the sheath has a circular cross-section in a cross-sectional plane that is aligned normal to a longitudinal axis of the threaded rod, and an outer diameter of the sheath is larger than an outer diameter of the threaded rod, so that the thread flanks of the external thread are completely covered.

[0004] Advantageous further developments of the invention are the subject of the subclaims.

[0005] It is expedient if the coating is designed as a coating and is applied to the external thread of the base body in a material-to-material manner. The coating can be applied, for example, by spraying a hardenable liquid onto the threaded rod, in particular while the threaded rod rotates relative to a spray nozzle, or by accommodating the threaded rod in a mold and performing a casting process, in particular a die-casting process or an injection-molding process.

[0006] Preferably, the sheath is made of a plastic material. Particularly suitable for this purpose are dimensionally stable plastic materials that exhibit a favorable coefficient of friction and high wear resistance, such as polyetheretherketones (PEEK plastics) or polyoxymethylenes (POM plastics, also known as polyacetals).

[0007] It is advantageous if a transmitter element for a sensor or a sensor is embedded in the casing. A transmitter element for a sensor can, for example, be designed as a permanent magnet, which can be used to determine the relative position of the piston rod in relation to the cylinder housing, in particular in relation to the end cover. In this case, the transmitter element can be scanned, for example, by a Hall sensor assigned to the cylinder housing with downstream evaluation electronics. The casing can also be used to embed a sensor in order to enable the detection of a physical variable such as temperature directly on the piston rod. The sensor is preferably designed for wireless signal transmission in order to avoid complex cabling.RFID sensors in particular can be used for this purpose, where the energy for operating the sensor is wirelessly coupled into the sensor and sensor signals provided by the sensor can be read wirelessly.

[0008] In a further development of the invention, it is provided that the sheath is designed as a sleeve and is fixed in a form-fitting and / or material-fitting manner to the external thread of the base body. For example, the sheath is designed as a circular-cylindrical sleeve that is pushed onto the threaded rod and is fixed in the desired position in a form-fitting manner by a forming process or is fixed in a material-fitting manner by an adhesive process. Alternatively, it can also be provided that the sleeve is provided with an internal thread that is adapted to the external thread of the threaded rod, so that the sleeve can be screwed onto the threaded rod and fixed in the desired position by a forming process or an adhesive process. The sleeve can also be fixed in the desired position with a threaded component such as a nut that is screwed onto the threaded rod.

[0009] In a further embodiment of the invention, the sleeve is made of at least one material from the group consisting of plastic, glass, and metal. Optionally, the sleeve can be made of one of the following materials: plastic, glass, or metal, or a composite of several of the following materials: plastic, glass, and metal. A combination of plastic and metal may be of particular interest, with the sleeve having, in particular, an outer shell made of metal and an inner shell made of plastic.

[0010] It is advantageous if the working piston is screwed onto the external thread of the piston rod and / or rests positively against an axial end face of the casing. The existing external thread of the threaded rod can thus be used to attach the working piston to the piston rod. It is preferred that the working piston rests against the casing, thus creating a mutual support function with the casing.

[0011] In an advantageous development of the invention, an end section of the piston rod facing away from the working piston, which is arranged outside the cylinder housing, is provided with a coupling element that is screwed onto the external thread of the piston rod. This coupling element serves, for example, as a connection to a movable part of a device that can be driven by the pneumatic cylinder. For example, the coupling element is designed as a screw sleeve with a ball socket attached to the end. The coupling element is screwed onto the piston rod with an internal thread. The ball socket can be connected to a ball head that is attached to the movable part of the device that is to be moved by the pneumatic cylinder.

[0012] Preferably, the external thread on the base body is produced using a non-cutting thread manufacturing process. This enables cost-effective production of the threaded rod. Furthermore, a threaded rod produced in this way exhibits advantageous fatigue strength properties due to the material hardening that typically occurs in a non-cutting thread manufacturing process.

[0013] In a further embodiment of the invention, it is provided that the base body is made of iron or steel or aluminum or plastic.

[0014] Advantageous embodiments of the invention are illustrated in the drawing. Fig. 1 a schematic sectional view of a pneumatic cylinder with a first embodiment of a piston rod formed from a threaded rod with a casing, Fig. 2 a strictly schematic cross-sectional view of the piston rod according to the Fig. 1, Fig. 3 is a strictly schematic cross-sectional view of a portion of the first embodiment of a piston rod, Fig. 4 is a strictly schematic cross-sectional view of a portion of a second embodiment of a piston rod, and Fig. 5 a strictly schematic cross-sectional view of a portion of a third embodiment of a piston rod. One in the Fig. The pneumatic cylinder 1 shown in Figure 1 serves to convert pneumatic energy from a pressurized fluid, for example compressed air, into a linear actuating movement. For this purpose, the pneumatic cylinder 1 has a cylinder housing 2 which is formed from a profile part 3, a first end cover 4 attached to the end of a first end face 21 of the profile part 3, and a second end cover 5 attached to the end of a second end face 22 of the profile part 3 facing away from the first end face 21. The profile part 3 is designed, for example, as an extruded aluminum part and extends with a constant profile along a movement axis 6. The profile part 3, together with the first end cover 4 and the second end cover 5, delimits a working recess 18 which has a circular cross-section in a cross-sectional plane (not shown) oriented transversely to the movement axis 6.For a pressure-tight design of the working recess 18, a spacer 22 is provided between the first end face 21 and. A first, circular sealing ring 23 is arranged on the first end cover 4. Furthermore, a second, circular sealing ring 24 is arranged between the second end face 22 and the second end cover 5.

[0015] Arranged in the working recess 18 are a working piston 10, purely exemplary in its circular cylindrical configuration, and a piston rod 7 connected to the working piston 10. The piston rod 7 extends with a circular cross-section along the movement axis 6. The piston rod 7 passes through a through-bore 25, which is formed in the first end cover 4, and extends beyond the cylinder housing 2 along the movement axis 6.

[0016] For a linearly movable seal between the piston rod 7 and the first end cover 4, a piston rod seal 12 designed purely as an example as a double lip seal is provided in the through hole 25, which seals against an outer surface 26 of the piston rod 7 serving as a sealing surface.

[0017] Furthermore, a plain bearing sleeve 13 is arranged in the through-bore 25 in the axial direction adjacent to the piston rod seal 12, which sleeve also bears against the outer surface 26 of the piston rod 7 and which is designed for a plain bearing of the piston rod 7 relative to the first end cover 4.

[0018] The working piston 10, together with the working recess 18, defines a first working chamber 27 of variable size and a second working chamber 28 of variable size. Both the first working chamber 27 and the second working chamber 28 can be supplied with or vented with compressed air via working connections not shown in detail in order to thereby create a pressure difference between the two working chambers 27, 28 and thus a resulting pressure force on the working piston 10.

[0019] As the representations of the Fig. 1 and Fig. 2, the piston rod 7 is formed by a threaded rod 8 and a casing 9. The threaded rod 8 forms the base body of the piston rod 7, while the casing 9, which extends in the case of the piston rod 7 in a central longitudinal section of the threaded rod 8, forms the outer surface 26 for the sealing engagement of the piston rod seal 12 and for the sliding bearing with the sliding bearing sleeve 13. The threaded rod 8 can be made purely by way of example from metal or plastic and is, in the illustrated embodiment, the Fig. 1 and Fig. 2 is provided with an external thread 11 over its entire length, which can be designed with one or more threads. The casing 9 is in the embodiment of the piston rod 7 according to the illustration of the Fig. 1 and Fig. 2 is designed as a plastic coating, which was applied to the threaded rod 8, for example, using a plastic injection molding process. By way of example, an RFID sensor 17 is incorporated into the casing 9, which can be wirelessly supplied with energy from a transmitter (not shown) arranged away from the pneumatic cylinder 1 and which, with wirelessly supplied energy, can emit a sensor signal, for example a temperature signal, which can be received and evaluated by a suitable receiver (not shown). In addition to or as an alternative to the RFID sensor 17, a permanent magnet serving as a transmitter can be embedded in the casing. This permanent magnet can be scanned by a suitable sensor, for example to detect the position of the piston rod 7 relative to the cylinder housing 2.

[0020] At a first end region 31 of the piston rod 7 arranged outside the working recess 18, a coupling sleeve 33 is screwed onto the threaded rod 8, which coupling sleeve has, purely by way of example, an annular coupling section 34. The coupling section 34 can be used for pivotally movable attachment to a joint ball (not shown) of a ball joint of a device (also not shown) to which the pneumatic cylinder 1 is assigned to provide movement.

[0021] The working piston 10 and a lock nut 14 for the working piston 10 are screwed onto a second end region 32 of the piston rod 7 arranged within the working recess 18, so that a direct, positive force transmission between the working piston 10 and the piston rod 7 is ensured.

[0022] The working piston 10 rests axially against the casing 9 with an axially aligned end face 15, which thus forms a positively acting support element for the working piston 10.

[0023] As the detailed representation of the Fig. 3, in the case of the piston rod 7, the external thread 11 is completely surrounded over the entire circumference by the sheath 9 made of plastic, so that the thread flanks 16 of the threaded rod 8, which is shown without hatching for reasons of clarity, are completely covered and a purely exemplary circular-cylindrical outer surface 26 is realized.

[0024] As the detailed representation of the Fig. 4, in the second embodiment of a piston rod 57, the external thread 11 is completely surrounded over its entire circumference by the casing 59 designed as a screw sleeve 60, so that the thread flanks 16 of the threaded rod 8, shown without hatching for reasons of clarity, are completely covered and a purely exemplary circular-cylindrical outer surface 66 is realized. In this case, the screw sleeve 60, provided with an internal thread 61, is positively secured to the threaded rod 8.

[0025] As the detailed representation of the Fig.5, in the third embodiment of a piston rod 67, the external thread 11 is completely surrounded over its entire circumference by the sheath 69 designed as a cylindrical sleeve 70, so that the thread flanks 16 of the threaded rod 8, shown without hatching for reasons of clarity, are completely covered and a purely exemplary circular-cylindrical outer surface 76 is realized. In this case, the sleeve 70 is firmly fixed to the threaded rod 8 with an adhesive layer 71.

Claims

[1] Pneumatic cylinder (1) for providing a linear movement, with a cylinder housing (2) in which a working recess (18) is formed, in which a working piston (10) is received so as to be linearly movable along a movement axis (6), wherein the working piston (10) is connected to a piston rod (7; 57; 67) which passes through an end cover (4) arranged on the end side of the cylinder housing (2), which end cover has a piston rod seal (12) which bears sealingly against a sealing surface (26) of the piston rod (7; 57; 67), characterized by that the piston rod (7; 57; 67) has a base body (8) designed as a threaded rod and an external thread (11) of the base body (8) is provided at least in regions with a covering (9; 59; 69) from the group: coating, sleeve, which covers the external thread (26) and serves as a sealing surface (26) for the piston rod seal (12). [2] Pneumatic cylinder (1) according to claim 1, characterized bythat the covering (9) is designed as a coating and is applied in a material-locking manner to the external thread (11) of the base body (8). [3] Pneumatic cylinder (1) according to claim 2, characterized by that the casing (9) is made of a plastic material. [4] Pneumatic cylinder (1) according to claim 2 or 3, characterized by that a sensor element for a sensor or a sensor (17) is embedded in the casing (9). [5] Pneumatic cylinder (1) according to claim 1, characterized by that the sheath (69) is designed as a sleeve (70) and is fixed in a form-fitting and / or material-fitting manner to the external thread (11) of the base body (8). [6] Pneumatic cylinder (1) according to claim 5, characterized by that the sleeve (70) is made of at least one material from the group: plastic, glass, metal. [7] Pneumatic cylinder (1) according to one of the preceding claims, characterized bythat the working piston (10) is screwed onto the external thread (11) of the piston rod (7; 57; 67) and / or bears positively against an axial end face of the casing (9; 59; 69). [8] Pneumatic cylinder (1) according to one of the preceding claims, characterized by that an end section (31) of the piston rod (7; 57; 67) facing away from the working piston (10), which is arranged outside the cylinder housing (2), is provided with a coupling element (33) which is screwed onto the external thread of the piston rod (7; 57; 67). [9] Pneumatic cylinder (1) according to one of the preceding claims, characterized by that the external thread (11) on the base body (8) is produced using a non-cutting thread production process. [10] Pneumatic cylinder (1) according to one of the preceding claims, characterized by that the base body (8) is made of iron or steel or aluminum or plastic.

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