EP0737282B1

EP0737282B1 - Cylinder with a non-rotatable piston rod

Info

Publication number: EP0737282B1
Application number: EP95905263A
Authority: EP
Inventors: Lennart Forsberg
Original assignee: Rexroth Mecman AB
Current assignee: Rexroth Mecman AB
Priority date: 1993-12-30
Filing date: 1994-12-14
Publication date: 1999-06-16
Anticipated expiration: 2014-12-14
Also published as: WO1995018322A1; SE9304352L; DE69419177D1; DE69419177T2; SE509233C2; EP0737282A1; SE9304352D0

Description

The present invention concerns a device in a fluid pressure cylinder, in particular in a pneumatic cylinder, for non-rotatable mounting of a piston rod protruding through a cylinder end wall and being connected to a piston, which is displaceable in a cylinder tube between two cylinder end walls.

Such devices are being used in cases where the piston rod carries a tool, a holder or the like which must not turn or rotate during the working stroke of the piston, although the particular tool, holder or the like is exposed to a torque. In order to achieve a non-rotatable mounting of the piston rod, one has previously used an arrangement with a fixed shaft with splines, one end of which is fastened to an end wall of the cylinder so as to extend along the central axis of the cylinder, the piston having a central hole with a bushing, which is non-rotatably guided along the splines-shaft. The piston is connected to a tubular piston rod portion, which encloses the splines-shaft and extends through the opposite cylinder end wall, where it is connected, e.g., to an external piston rod portion.

This arrangement operates very well in many cases but has the following drawbacks:

it is complicated and expensive;
assembly of the various parts is time-consuming;
a certain unintentional turning may occur because the splines-shaft is not rigid enough, especially when the piston is located in its end position opposite to the fastened end of the splines-shaft. The problem becomes worse for very long strokes;
a turning movement may also occur because of a play between the piston bushing and the splines-shaft; because of wear, the play increases with time.

Another device is known from the German published application DE-A-2637290, wherein a fluid pressure cylinder having three internal tension rods is described. The three tension rods also serve as guiding rods and pass through respective holes in the piston. Each rod is anchored to the end walls by means of threaded bolts engaged in threaded recesses in the end wall and the rod, respectively.

However, in order to achieve a perfect alignment of the guiding rods, mutually as well as in relation to the central axis of the cylinder tube, it is necessary to manufacture the various parts with very exact dimensions. Therefore, the fluid cylinder will be rather difficult and expensive to manufacture.

The object of the present invention is to accomplish a device of the kind indicated above, which does not have the above-mentioned drawbacks and which is thus simpler and less expensive as well as more wear-resistant and rigid than the previously known devices.

This object is achieved for a fluid pressure cylinder having at least one rectilinear guiding rod extending axially between the two cylinder end walls and, with a sliding fit, axially through a sealed opening through the piston at a radial distance from the central axis of the cylinder tube, wherein the end portions of the guiding rod are mounted in fastening means at each cylinder end wall, the device being characterized in that at least one of the fastening means is adjustable, at least circumferentially, in connection with the assembly of the fluid pressure cylinder to enable an exact alignment of the guiding rod in parallel to the central axis of the cylinder tube, said fastening means being fixed in position from the outside upon adjustment thereof.

Because the guiding rod is located at a radial distance from the central axis, it will effectively counteract a torque acting on the piston rod outside the cylinder. Furthermore, the guiding rod is fixed at both ends, and therefore the rigidity of the device is very good adjacent to each end position of the piston.

Manufacture and assembly of the device is facilitated by aligning the guiding rod only in connection with the assembly. Hereby, it is possible to dispense with close manufacturing tolerances for the fastening means.

Advantageous further features are stated in the dependent patent claims and will be apparent from the detailed description below, related to a preferred embodiment.

Thus, a preferred embodiment of the invention is described below with reference to the the appended drawings.

Fig. 1 is a side-view, partially in longitudinal section, of a pneumatic cylinder according to the invention;

Fig. 2 shows a part of the cylinder in a larger scale, in the area between the cylinder tube and one of the cylinder end walls; and

Fig. 3 shows, likewise in a larger scale, the axial passage of the guiding rod through the piston.

In Fig. 1 there is shown a pneumatic cylinder substantially comprising a cylinder tube 1, two

cylinder end walls

2,3 at each end of the cylinder tube, a piston 4 displaceable inside the cylinder tube 1, and a piston rod 5, which is fastened to the piston 4 and extends through one of the cylinder end walls, i.e. the cylinder end wall 3. In this embodiment, the cylinder tube 1, the

cylinder end walls

2,3 and the piston 4 are made of aluminum, whereas the piston rod 5 is made of stainless steel.

The cylinder tube 1 shown in Fig. 1 is relatively short and may be much longer in a practical case. As known in the art, the piston 4 is provided with damping shoulders 4a, which cooperate with central recesses in the

end walls

2,3 for damping the piston movement at each end position, and with annular elements around the circumference, i.e. a slide guiding ring 6 of rigid plastic material having a low friction against the inside of the cylinder tube 1 and two sealing rings 7 made of elastic material, located axially on both sides of the slide guiding ring 6 and each having a lip 7a sealing effectively against the cylinder tube. Compare Fig. 3.

The pneumatic cylinder is also provided with ordinary tension rods 8, which hold the

end walls

2, 3 towards the ends of the cylinder tube 1, and with pressurized

air connections

9, 10 in the

end walls

2, 3 for controlling the movement of the piston 4.

The parts of the pneumatic cylinder described so far are well known. According to the present invention, a guiding rod 11 is mounted inside the cylinder and extends between the

end walls

2,3 axially through a through-going, sealed hole 12 in the piston 4. The guiding rod 11, which is made of stainless steel in this embodiment, will hereby maintain the piston 4 in a well defined angular position relative to the cylinder tube 1, and the

end walls

2,3 and can resist a torque, which is exerted on the piston rod 5 from the outside. Such a torque resistance of the piston rod 5 and the piston 4 becomes especially effective because the guiding rod 11 is located at a distance from the central axis L, so that the radial lever, i.e. the distance between the central axis L and the guiding rod 11, is substantial. Preferably, this distance is greater than half the radius of the cylinder tube 1.

For a proper operation of the pneumatic cylinder, it is essential that the guiding rod 11 is aligned exactly in parallel to the central axis L, so that the friction is low and wear is avoided as far as possible. For this purpose, the ends of the guiding rod 11 are fastened at the

end walls

2, 3 in such a way that an adjustment of the fastening can be made in connection with the assembly.

The fastening means for the guiding rod 11 are constituted by

corresponding holes

13a and 14a, respectively, which are bored axially in an

insert ring

13 and 14, respectively, located at each

end wall

2, 3. The

insert ring

13 and 14, respectively, is made of aluminum in the embodiment and has a circumferential flange 13b and 14b, respectively, which is fitted into an

annular groove

15 and 16, respectively, in the

end wall

2, 3 partially in the region of the extension of the cylinder tube 1. Compare Fig. 2.

In advance, the

holes

13a, 14a are bored at exactly the same radial distance from the center as the through-going hole 12 in the piston 4. When the cylinder is assembled, the

insert rings

13, 14 are fitted with their circumferential flanges 13b, 14b into the respective

end wall groove

15, 16, and the cylinder tube 1 is pulled together rather loosely between the

cylinder end walls

2, 3, e.g. by manual tightening of the nuts of the tension rods 8. At this point, each

insert ring

13, 14 may be turned around circumferentially.

During assembly, the

holes

13a, 14a are positioned approximately opposite to each other and approximately in parallel to the central axis L, and the guiding rod 11 is fitted with its end portions into the two

holes

13a, 14a. Thereupon, the piston 4 is displaced back and forth by means of the piston rod 5, and the

insert rings

13, 14 will then be automatically positioned circumferentially when the piston 4 reaches each end position. In this way, a fine positioning is achieved, so that the guiding rod is aligned exactly in parallel to the central axis L.

Thereupon, the tension rods 8 are tightened to a given tensile value, so that the circumferential flanges 13b, 14b of the

insert rings

13, 14 are clamped between the respective ends of the cylinder tube 1 and the bottom of each

annular groove

15, 16. The necessary sealing is obtained by means of sealing rings 17, 18 (see Fig. 2), which are inserted in corresponding grooves and seal against the inside of the cylinder tube 1 and against the radially outer limiting wall of the annular groove 15 in the end wall, respectively. As appears from Fig. 2, the guiding rod 11 has a certain axial play between the

end walls

2 and 3, whereby the guiding rod 11 is kept exactly straight even after clamping the cylinder tube 1 between the

end walls

2, 3.

Upon axial tightening of the tension rods 8, the insert rings are clamped in a respective angular position holding the guiding rod exactly aligned in parallel to the central axis L. However, if so desired, each

insert ring

13, 14 can be locked in such a position, e.g., by boring a hole 19 radially from the outside through the

end wall

2, 3 and in a certain distance 20 into the circumferential flange 13b of the insert ring, whereupon a locking pin 21 is inserted, which holds the insert ring in position with a tight fit relative to the end wall. Since the

holes

19, 20 are located axially between the

sealing rings

17, 18, there will be no leakage of pressurized air in the region of the locking pin 21. Alternatively, the insert ring may be locked by a screw extending axially through the

end wall

2, 3 and preferably being sealed by means of a hardening glue.

The through-passage of the guiding rod 11 through the piston 4 is shown clearly in Fig. 3. The central portion of the through-going hole 12 has a bushing 22 fitted therein which has a low friction against the guiding rod 11. The necessary seal is obtained by means of

lip sealing rings

23, 24, which are positioned axially on each side of the bushing 22 and which are held in place by means of

washers

25, 26, e.g., made of spring steel.

It should be pointed out that the adjustability of the fastening means of the guiding rod 11 can be obtained in various ways. Instead of insert rings with holes, it is possible to use a small holding body, which is somewhat movable during assembly, e.g., in a corresponding recess in the end wall, and which is fixed in position by means of a screw extending axially through the end wall of the like.

Finally, it is possible to let one end of the guiding rod be fixed from the start and only adjust the opposite end thereof in connection with the assembly.

Claims

A device in a fluid pressure cylinder for non-rotatable mounting of a piston rod (5) protruding through a cylinder end wall (3) and being connected to a piston (4), which is displaceable in a cylinder tube (1) between two cylinder end walls (2, 3), wherein at least one rectilinear guiding rod (11) extends axially between the two cylinder end walls (2, 3) and, with a sliding fit, axially through a sealed opening (12) through the piston at a radial distance from the central axis (L) of the cylinder tube (1), and wherein the end portions of the guiding rod (11) are mounted in fastening means (13a, 14a) at each cylinder end wall (2, 3), characterized in that at least one of the fastening means is adjustable, at least circumferentially, in connection with the assembly of the fluid pressure cylinder to enable an exact alignment of the guiding rod in parallel to the central axis (L) of the cylinder tube, and in that said fastening means is fixed in position from the outside upon adjustment thereof.
Device according to claim 1, characterized in that both of said fastening means (13, 14) are adjustable.
Device according to claim 1 or 2, characterized in that each of the fastening means (13a, 14a) is adjustable by displacing the piston (4) between its end positions upon assembly of the fluid pressure cylinder.
Device according to any one of claims 1 - 3,
characterized in that the guiding rod (11) is mounted with an axial play at at least one of the cylinder end walls (2, 3).
Device according to any one of claims 1 - 4, characterized in that each fastening means is disposed at an insert ring (13, 14) of rigid material, located at the inside of the associated cylinder end wall, said insert ring being movable upon assembly of the fluid pressure cylinder.
Device according to claim 5, characterized in that the respective insert ring (13, 14) is kept radially fixed but is circumferentially rotatable relative to the cylinder end walls (2, 3) upon assembly of the fluid pressure cylinder.
Device according to claim 6, characterized in that each insert ring (13, 14) is fixed in position by clamping an outer flange (13b, 14b) thereof between the associated cylinder end wall (2, 3) and the cylinder tube (1).
Device according to claim 6 or 7, characterized in that each insert ring (13, 14) is fastenable by means a locking means (21) insertable from the outside of the cylinder end wall.
Device according to any one of claims 5 - 8,
characterized in that said fastening means comprises an axial recess (13a, 14a) in the respective insert ring (13, 14), said axial recess being dimensioned to receive an end portion of the guiding rod with a sliding fit and being bored at the same radial distance from the center as the axially through-going opening (12) in the piston.
Device according to any one of the preceding claims, characterized in that a bushing (22) is inserted in the axially through opening (12) of the piston, sealing rings (23, 24) being inserted axially on both sides of the bushing for sealing between the guiding rod (11) and the piston (4), which sealing rings (23, 24) are fastened by means of washers (25, 26).