EP0233500B1 - Pressure fluid driven actuator - Google Patents

Abstract

1. A pressure medium driven actuator, comprising an elastomeric bellows (1), preferably rotationally symmetric, which is sealingly arranged with its axial ends between two housing parts (2, 3), as well as a guide element (6) which passes axially through the interior of the bellows and is connected securely to the first housing part (3) and is mounted on the second housing part (2) in a guide (9), enabling axial relative movement between said housing part and the said guide element (6) ; characterised in that : for achieving inner guidance of the two housing parts (2, 3), a sliding or rolling bearing (9) arranged on the second housing part (2) is provided between the second housing part (2) and the guide element (6), which bearing is provided with a slip-ring-seal which seals the pressure chamber (7) of the bellows (1), and the sliding or rolling bearing (9) is constructed such that the guide element (6) is mounted on the second housing part (2) to enable only movement in the axial direction.

Description

The invention relates to an actuating device working with a pressure medium, with a rubber-elastic, preferably rotationally symmetrical bellows, which is arranged with its axial end faces between two housing parts in a medium-tight manner, and a guide element which passes axially through the interior of the bellows and is firmly connected to the first housing part and is mounted on the second housing part in a guide enabling an axial relative movement between this housing part and the guide element.

Actuators can be divided into three groups.

The first type of these actuators include air cylinders, e.g. according to DIN 24 335, which essentially consist of a pressure-tight housing, a piston guided therein and a piston rod connected to the piston or two piston rods, one on each piston side, with associated seals and bearings for the piston rod in the housing. These compressed air cylinders are used on a large scale because they enable the machine element controlled with them to be actuated precisely and reliably over a long operating time. Nevertheless, they have two basic disadvantages. One disadvantage is the required guiding accuracy between the pressure housing on the one hand and the piston on the other hand and the piston rod or piston rods on the one hand and the associated housing-side bearing on the other hand. These fits must be made with small tolerances, because there is a static match between the piston guide and the piston rod guide. The further fundamental disadvantage of these compressed air cylinders is the fact that they are very long, in particular in the upper diameter range, and have large weights. The large overall length arises, among other things due to the useful stroke to be kept in the cylinder chamber and the inevitably following one-sided or double-sided piston rod guide.

The second group of hydraulic or pneumatic actuators includes membrane cylinders. In these cylinders, the diaphragm, which is either clamped or lies loosely on a piston, has taken over the sealing function of the piston seal on the housing cylinder wall, which eliminates a problematic pair of fits compared to the compressed air cylinders. However, there is still the disadvantage of the large weights of these membrane cylinders, since a rigid cylinder housing is present. In this context, the necessary two-part design of this housing for clamping the membrane also has a negative effect. Furthermore, the operating pressure and the achievable stroke are limited in this type of actuators.

Finally, the third category of relevant actuators relates to bellows cylinders. In these, the pressure space for the pressure medium is essentially limited by a rotationally symmetrical bellows, which is designed to be retractable and retractable by corresponding folds in the direction of the axis of rotation. Bellows cylinders of this type, measured on the two types of actuators discussed above, have a low installation height, a low weight, a large force development and fewer moving parts. However, for certain applications, in particular for the substitution of piston or membrane cylinders, they have a decisive disadvantage. You yourself have no axial guidance, so that when used as an actuating device for a machine element either this must be performed accordingly or a separate guide of the working cylinder 5 must be attached outside the bellows. This is extremely expensive, including also because these guides must be outside the largest bellows diameter. A second disadvantage compared to piston cylinders, e.g. according to DIN 24 335, lies in the fact that bellows cylinders may only be moved together up to a certain length of restaxi. The remaining dead volume to be filled by the medium during a working stroke makes their use very uneconomical, especially for short strokes.

An actuating device equipped with a bellows of the type assumed at the outset is the subject of DE-A 3 032 638. This known actuating device is primarily designed as a jack for developing relevant tractive force; but it is also intended to be used as a servo cylinder.

The known actuating device consists essentially of a rotationally symmetrical bellows, which is arranged with its axial end faces between two housing parts, and a guide element which extends axially inside the bellows. While one end of the axial guide element is firmly connected to the first housing part, its second end passes through a central opening in the second housing part with play. To seal this guide, which is subject to play, between the central opening of the second housing part and the guide element, a second bellows is provided, which is smaller than the first and is rotationally symmetrical and is also axially penetrated by the guide element. On the one hand, this bellows is fastened tightly to the second housing part outside the central opening, while on the other hand it is closed off by a plate. The two bellows themselves are in communicating connection through the gap between the central opening of the second housing part and the guide element. A seal between the plate and the guide element with respect to the pressure space of the two bellows is achieved in that the plate is welded to the guide element.

This known actuating device also has disadvantages. A disadvantage is that the second bellows acts counter to the first, so that the usable pressure area of the first is reduced by the cross-sectional area of the second bellows.

Furthermore, for a given stroke length, the length of the device is increased by the length of the second bellows. 1 of DE-A 3 032 638 is the second, i.e. Smaller bellows, arranged outside the first, larger bellows and both bellows must be coordinated in terms of stroke so that the working stroke can be driven by both bellows. It is therefore practically twice the installation length compared to commercially available bellows cylinders. Even in the embodiments shown in FIGS. 2 and 3 of DE-A 3 032 638, in which the second, smaller bellows is laid in the first larger bellows, the overall length cannot be reduced very much because the second bellows does not more allowed to move the first bellows to its minimum exit height in order to do its work from this minimum exit height. In the embodiments according to FIGS. 1 and 2 of DE-A 3 032 638, the useful stroke must be present twice, i.e. similar to the piston and diaphragm cylinders. Since the useful stroke of a bellows cylinder with a small diameter is naturally smaller than that of a larger one, the small one, i.e. second bellows, determining the stroke, i.e. the greatest usable stroke length for the larger bellows has to be bought for a larger overall length (initial length) for the smaller bellows. This results in the already discussed basic length compared to commercially available bellows cylinders, with the same stroke being increased even further (minimum starting length) in these designs according to DE-A 3 032 638. In their construction according to FIG. 3, the minimum overall length is predetermined by the fixed dimension between the first housing part of the first bellows and the opposite end plate of the second bellows and the minimum length of this second bellows.

Finally, due to the play or gap necessary for the passage of the medium, there is no exact axial guidance of the actuating device between the central opening of the second housing part and the guide element for connecting the two bellows. The head plate and end plate can namely assume an inclined position, the center point of the swivel radius being at the level of the central opening. This device can therefore not easily be used to drive machine elements. Rather, either the machine element is to be guided accordingly or an axial guide lying outside the first, larger bellows is to be provided between the two housing parts, between which the first bellows is clamped. As already discussed, the latter is expensive and leads to an increase in the diameter of the overall construction.

The object of the invention is to provide an actuating device of the type assumed at the outset, in which the advantages of bellows cylinders with which the piston cylinder or the membrane cylinder are combined as far as possible are emphasized.

This object is achieved in an actuating device with the features mentioned in that, in order to achieve an internal guidance of the two housing parts between the second housing part and the guide element, a slide or roller bearing arranged on the second housing part is provided, which is provided with a mechanical seal sealing the pressure chamber , and that the sliding or rolling bearing is designed such that the guide element is mounted on the second housing part while allowing only one movement in the axial direction.

The actuating device according to the invention combines the advantages of a bellows construction on the one hand and the piston cylinder or membrane cylinder on the other hand, but avoiding their design-specific disadvantages. It is namely short and lightweight for a given stroke, since the length of the construction is primarily determined only by the stroke length and the length of the guide between the second housing part and the guide element and the pressure space is essentially limited by the bellows. The actuating device according to the invention builds in proportion the smaller the longer the useful stroke becomes. It is also characterized by an exact guidance between the stationary and the movable housing part, so that it can be used without further measures for actuating machine elements that are to be guided exactly. Compared to the piston cylinders or membrane cylinders, however, the piston and the associated guides or bearings can be omitted in the arrangement according to the invention. Finally, the actuating device according to the invention is characterized by a simple structure, since both the guide element with the housing part with which it is firmly connected and the guide for the guide element with the second housing part can each be formed in one piece. Overall, there are considerable advantages in terms of space requirements, the use of materials and the costs.

Expedient developments of the actuating device according to the invention can be seen in the following features.

An advantageous embodiment of the invention consists in that the guide element is a bolt with a circular cross-section, and the guide between the guide element and the second housing part is designed as a slide or roller bearing arranged in the latter, which is provided with a mechanical seal on the pressure chamber side. Standard components can thus be used, thereby further reducing the cost of the actuating device according to the invention.

To further save weight, it is expedient for the guide pin to be hollow.

To achieve a particularly compact and robust construction, it is recommended that the guide between the guide element and the second housing part lies within the interior space defined by the bellows.

To save pressure medium and to reduce the power required to operate the actuating device according to the invention, it is advantageous that a housing element is provided in the interior of the bellows, which the dead volume of the bellows is reduced, as a result of which significant energy savings are achieved, in particular in the case of short strokes compared to known bellows cylinders.

This housing element can either be a separate one or it can also be formed by the second housing part, which for this purpose is drawn into the interior of the bellows in such a way that the dead volume of the bellows is also reduced.

For the simplest possible adjustment of the stroke length of the actuating device according to the invention, it is advisable to arrange an axially adjustable stop member on the guide element.

Another embodiment of the invention is that at least one damping element acting between the two housing parts is arranged in the interior of the bellows, which is preferably represented by an industrial shock absorber (Fig. 4a).

A particularly expedient embodiment of an actuating device according to the invention, which is double-acting, results from the fact that the reset device is also represented by a bellows construction.

Furthermore, it may be expedient that the two housing parts of the bellows are rotatably guided to one another. In this way, even in cases where a torque is exerted on one of the housing parts of the actuating device, an exact guidance of the machine element to be actuated is ensured and, moreover, a damaging twisting of the bellows about its axis is prevented.

Finally, a further exemplary embodiment of the invention consists in that instead of or in addition to a longitudinal guide arranged in the center of the device, several longitudinal guides with a diameter on the periphery of the housing parts but penetrating the bellows are provided. Such an arrangement offers particular advantages if the load or force attack occurs off-center on the movable housing part. Furthermore, an anti-rotation lock of the housing parts is automatically connected to one another. The central area in the middle of the device is free (if necessary) for the central arrangement of a shock absorber, which therefore no longer has to be arranged in pairs or symmetrically to several. The arrangement of a compression spring for the bellows return can also advantageously be carried out in the center.

Embodiments of the actuating device according to the invention are explained below with reference to the accompanying drawings.

• Fig. 1 einen teilweisen Axialschnitt einer ersten Ausführungsform der erfindungsgemäßen Betätigungseinrichtung,
• Fig. 2 einen teilweisen Axialschnitt einer zweiten Ausführungsform der erfindungsgemäßen Betätigungsvorrichtung,
• Fig. 3 einen Axialschnitt durch eine dritte Ausführungsform der erfindungsgemäßen Betätigungsvorrichtung,
• Fig. 4 einen Axialschnitt durch eine vierte Ausführungsform der erfindungsgemäßen Betätigungsvorrichtung, wobei zwei unterschiedliche Varianten dargestellt sind,
• Fig. 4a eine weitere Ausbildung der Anordnung nach Fig. 4, und
• Fig. 5 eine weitere grundsätzliche Ausführungsform der Erfindung.
• Fig. 6 bis 11 sind Darstellungen weiterer Ausführungsformen der Erfindung.

It shows:

• 1 is a partial axial section of a first embodiment of the actuating device according to the invention,
• 2 shows a partial axial section of a second embodiment of the actuating device according to the invention,
• 3 shows an axial section through a third embodiment of the actuating device according to the invention,
• 4 shows an axial section through a fourth embodiment of the actuating device according to the invention, two different variants being shown,
• 4a shows a further embodiment of the arrangement according to FIG. 4, and
• Fig. 5 shows another basic embodiment of the invention.
• 6 to 11 are illustrations of further embodiments of the invention.

In the figures, identical or corresponding components are identified by the same reference symbols.

Thereafter, it includes printing media, e.g. Compressed air, operating actuating device a rotationally symmetrical bellows 1, which, as can be seen from FIG. 1, can either be folded only once or, as can be seen in the other figures, can be folded several times. The axial faces of the bellows are medium-tight, i.e. compressed air tight, between two e.g. arranged in cross section circular housing parts 2 and 3. The housing part 2 can be the part of the actuating device that is to be installed in a stationary manner, while the housing part 3 can be the actuating part that can be moved relative to it and that can be connected directly or indirectly to the machine element to be moved.

The medium-tight connection of the axial end faces of the bellows 1 to the housing parts 2 and 3 can be achieved in that the end flanges 1a of the bellows 1 are clamped by clamping rings 4 provided on the respective housing part 2, which are connected to the respective housing part 2 or 3 by means of screws 5 are screwed.

A guide element 6 in the form of a hollow guide pin, e.g. in one piece, integrally formed, which passes through the pressure space 7 defined thereby coaxially to the bellows 1. This guide element 6 is guided in a slide bearing 9, which is formed coaxially on the housing part 2, preferably in one piece. Towards the pressure chamber 7, the pair of guides 6, 8 and 9 is sealed pressure-tight by a mechanical seal 10.

A housing element in the form of a disk 11 is arranged in the pressure chamber 7 itself and is displaceably or fixedly mounted on the guide element 6. The disk 11 reduces the volume dead space of the pressure chamber 7 in the manner already discussed.

As can be readily seen, when the pressure chamber 7 is appropriately loaded with pressure medium via a connection 17 and corresponding lines and valve arrangements, there is a relative movement between the housing parts 2 and 3, with the bellows 1 being stretched. the relative movement between the housing parts 2 and 3, a stop disk 12, preferably with screws 13, is fastened to the guide element 6 and comes to rest on the axial end face of the bearing housing 8 at the end of the stroke via an intermediate damping element 14.

The housing part 3 is reset to the starting position shown in FIG. 1 by releasing the pressure chamber 7 by means of a compression spring 15. which is clamped between shoulders on the stop plate 12 and the bearing housing 8 (single-acting version with integrated reset).

The embodiment according to FIG. 2 differs from that according to FIG. 1 in that the bellows 1 is folded several times and the disk 11 for reducing the dead volume of the pressure chamber 7 has a greater axial height than the disk 11 in accordance with the larger initial length of the bellows 1 1. Furthermore, a mounting plate 16 is indicated, on which the housing part 2 to be held stationary is mounted and fastened by means not shown.

The essence of the embodiment according to FIG. 3 can be seen in the fact that, in contrast to the constructions according to FIGS. 1 and 2, no separate disk 11 is provided for reducing the dead volume in the pressure chamber 7, but instead the housing part 2/3 accordingly trained, namely drawn into the pressure chamber 7 in a pot shape. Another difference is that 2/3 damping elements 14/3 are arranged on the axial inner end face of this housing part, on which the stroke limitation takes place. A reset mechanism is not shown in Fig. 3.

In contrast, the embodiment of FIG. 4 is supplemented by the fact that a reset mechanism working with pressure medium is provided. This also consists of a bellows 40, one axial end face of which, with respect to the pressure chamber 7, the outer end face of the housing part 2 is connected by a clamping ring 41, which is screwed to the housing part 2, 4 by screws 42, while the other is axial Front side is connected to an end plate 43, expediently also by means of a clamping ring 41 with screws 42. The end plate 43 is either, as shown on the left in Fig. 4, axially adjustable with respect to the guide element 6, for example Via two lock nuts 44, which are screwed onto a thread 6a of the guide element 6, or are fixed firmly on the guide element, as indicated on the right in FIG. 4, namely by a shoulder 6b on the lateral surface of the guide element 6 and a counter nut 44 In this way, in the embodiment on the left in FIG. 4, the stroke length of the arrangement can be set, while in the construction on the right in FIG. Damping elements 14/4 supplement the stroke limits of this arrangement.

Via a 4/2-way valve 46, the pressure chamber 7 of the bellows 1 is filled with pressure medium during the working stroke, while the pressure chamber 7 is emptied for the return stroke and the pressure chamber 47 is pressurized with the pressure medium.

According to Fig. 4a, the arrangement of Fig. 4 is further developed in that in the interior of the bellows in the housing part 2 e.g. two diametrically opposed industrial shock absorbers 18/4 are arranged, which interact with the movable housing part 2 and thus ensure a smooth driving into the end positions.

5 instead of the previously provided central guidance of the housing parts 2 and 3 on the periphery, but within the bellows 1 arranged longitudinal guides 6 are provided, which run in slide or roller bearings 9, which in turn are equipped with mechanical seals 10. There may be two or more such longitudinal guides 6, which are expediently distributed on a circle T with the same pitch. A shock absorber 18 can then be arranged centrally for damping.

FIGS. 6 to 9 show an embodiment of an actuating device according to the invention, in which end position damping is provided. In this embodiment, the bearing housing 8 is arranged penetrating the interior or pressure chamber 7 of the bellows 1. 6, which shows the one end position of the actuating device, the bearing housing 8 engages in a recess 3a (FIG. 7) of the first housing part 3, a space 7.1 for pressure medium remaining in the recess 3a above the upper end of the bearing housing. This space 7.1 increases when the relative movement between the housing parts is removed.

As can be seen from FIGS. 6 and 7, the bearing housing 8 comes out of the recess 3a of the first housing part 3 when pressure medium is introduced into the bellows 1.

The bearing housing 8 engages in the recess 3a of the first housing part 3 in such a way that a gap is formed between the bearing housing 8 and the first housing part, which gap is designated by 26 in FIGS. 6 and 8. Furthermore, a so-called damping ring 51 is arranged in a recess in the wall of the housing part recess 3a. This damping ring 51 has a sealing surface 55 which engages with the outer surface of the bearing housing 8 and which represents the radially inner surface of the damping ring 51. The lower axial end face 54 according to FIG. 8 is also designed as a sealing surface which can come into sealing engagement with the opposite groove wall. The radially outer surface and the upper axial end face of the damping ring 51 according to FIGS. 6 to 8 are provided with through-flow grooves (53, 52) for the pressure medium, as is known per se. Thus, by creating the play 26 between the bearing housing 8 and the housing part recess 3a and the arrangement of the damping ring 51, both a throttle connection and a check valve function between the space 7.1 in the housing part recess 3a above the upper end of the bearing housing 8 and the Interior 7 of the bellows 1 created.

The actuating device according to FIGS. 6 to 9 has a first or lower pressure medium supply 17.1, 20.1, 21, through which a pressure medium connection with the space 7 of the bellows 1 is created. As particularly shown in FIG. 9, for example, a plurality of vertical pressure medium supply channels 21 are provided. At least one of these channels 21 is connected via a bore 22 to a channel 24 which extends along the length of the bearing housing 8 and opens into the space 7.1 of the housing part recess 3a on its upper surface. Between the bore 22 and the channel 24, an adjustable throttle device 23, 25 is provided, as can be seen in particular from FIG. 9. This figure shows a throttle screw 25, by means of which the throttle opening between the channels 22 and 24 can be changed in size.

Finally, the actuating device according to FIGS. 6 to 9 also has a second upper pressure medium supply 17.2, 20.2, which is connected to the space 7.1 of the housing part recess 3a.

When executing the extension stroke, i.e. when the actuating device moves from the position according to FIG. 6 into the position according to FIG. 7, the interior or pressure space 7 of the bellows 1 is acted upon by pressure medium via the pressure medium supply 17.1, 20.1, 21. Here, pressure medium also flows via the throttle connection 22 , 23 and 24 in the space 7.1 of the housing part recess 3a. The damping ring 51 lies with its upper flow grooves 52 against the opposite wall of the groove receiving it. As a result, the pressure medium flowing into the interior 7 of the bellows 1 can pass through the gap 26 between the bearing housing 8 and the housing part recess 3a and the flow grooves 53, 52 on the surfaces of the damping ring 51 in question in the space 7.1 of the housing part recess 3a above of the bearing housing 8 penetrate. The entire pressure surface is thus acted upon and the bearing housing 8 is moved into the position shown in FIG. 7.

As long as there is a sealing engagement between the damping ring 51 and the bearing housing 8 during the relative movement between the bearing housing 8 and the housing part recess 3a, a vacuum is created in the space 7.1, which is caused by the pressure medium passing through the gap 26 and through the flow grooves 53 and 52 of the damping ring 51 flows, and by the pressure medium which passes through the adjustable throttle 23 into the channel 24, depending on the setting of the throttle screw 25, can not be filled up as quickly as it occurs during the relative movement mentioned. A stronger damping of the extension stroke results with a reverse installation of the damping ring 51 in such a way that the axial flow grooves 52 point downwards and the axial end face 54 points upwards. The medium then only has the option of filling up the vacuum created in room 7.1 via the throttle channels. The extension stroke can thus be damped in the desired manner.

During the retraction stroke, which is carried out after the control valve has been switched over under the action of external forces, there is again a sealing engagement between the damping ring 51 and the outer surface of the bearing housing 8. Thus, the pressure medium present in the space 7.1 above the bearing housing 8 becomes the further retraction movement of the bearing housing 8 compressed. Upon further retraction, the damping ring 51 passes through the pressure build-up in the space 7.1 with its lower axial end face 54 against the opposite groove wall, so that a pressure medium connection between the interior of the bellows 1 and the space 7.1 above the bearing housing 8 is no longer present. However, since the interior 7 of the bellows 1 is now depressurized, pressure medium can flow out of the space 7.1 via the channel 24 and the throttle opening 23 to the pressure medium supply 17.1. As a result of the presence of the throttle, the retraction stroke is damped. Less damping can in turn be achieved by the reverse installation of the damping ring 51.

If the extension stroke is to be damped using the upper pressure medium supply 17.2, 20.2, the upper ring flange of the space 7.1 is first filled when the pressure medium is supplied. At the same time, the medium flows through the gap 26 to the damping ring 51, which moves into its axially lower sealing position, so that no pressure medium can flow around the damping ring 51 into the interior 7 of the bellows 1. At the same time, further pressure medium flows through the channel 24, the bore 22 and the channel 21 throttled into the interior 7 of the bellows 1, because in this mode of operation the pressure medium supply 17.1 is closed. The entire effective area of the bellows cylinder is thus acted upon and the extension stroke is carried out. The resulting negative pressure in space 7 can only be compensated for via throttle ducts 24, 23, 22 and then via duct 21. Damping results in a manner analogous to that described in the previously described operating mode, in the desired weakened form also by the reverse installation of the damping ring 51.

After reversing the control device, the pressure medium supply 17.2 becomes depressurized, and the pressure medium flows out through the pressure medium supply 17.2 during the retracting movement. The damping ring 51 sits with its axially upper grooved end face 54 against the opposite groove wall, so that when there is a sealing engagement between the damping ring 51 and the outer surface of the bearing housing 8, the medium from the reducing pressure space 7 around the ring or through the channels 21, 22 , Throttle opening 23 and channel 24 can flow into the pressure chamber 7.1. This mounting position of the damping ring results in weaker damping. A stronger damping of the retraction stroke movement with the medium connection at 17.2 results if the damping ring with its axial sealing surface points upwards. The pressure medium in the interior 7 of the bellows 1 can now only escape via the channels 21 and 22, the throttle opening 23 and the channel 24 into the room or pressure chamber 7.1 and from there through the pressure medium supply 17.2. Thus, the bearing housing 8 moves into the housing part recess 3a with greater damping.

In a modified embodiment, not shown, two channels 24 are provided, each of which is connected to a pressure medium supply via an adjustable throttle. In addition, a check valve can be arranged in each channel 24, which blocks one channel 24 in one direction and the other channel 24 in the opposite direction. This makes separate adjustment of the extension stroke damping and the retraction stroke damping enables. In this case, the grooved damping ring is expediently replaced by a sealing ring that seals on both sides.

FIGS. 10 and 11 show a further embodiment of an actuating device according to the invention, in which the force-travel characteristic can be changed.

Bellows or bellows cylinders have the property of developing the greatest force at the beginning of their stroke. In a mostly non-linear degressive characteristic, the force drops to values between 75% and 50% of the initial lifting force up to the end of the stroke. This characteristic is caused by the initially large effective area when the bellows is folded, which the pressure medium strikes. With increasing expansion of the bellows, its diameter and thus the effective area become smaller.

10 shows an embodiment of an actuating device with a lower pressure medium supply 17.1, while a check valve 60 is provided in the upper pressure medium supply 17.2. The bearing housing 8 is stepped on the circumference, and the recess 3b of the first housing part receiving the bearing housing 8 has a corresponding stepped design. In the inner wall of each step of the housing part recess 3b there is a groove with a damping ring 51.1 or 51.2, which is of the same general type as was described in connection with FIGS. 6 to 9. The number of levels can be changed depending on the desired effect. The damping rings 51 are installed in such a way that the axially upper end face 54 is formed as a sealing surface and accordingly effects a seal when it engages with the opposite groove wall. The radially outer surface and the lower axial end surface are provided with through-flow grooves 53 and 54, respectively, while the radially inner surface 55 is again designed as a sealing surface. These radial sealing surfaces 55 of the rings 51 divide the total pressure space into the lower pressure space 7 and the upper pressure space 7.1 at the beginning of the stroke.

In the description of the extension stroke, it is initially assumed that the pressure medium is supplied via the feed 17.1. The medium flows through the channels 20.1 and 21 into the lower pressure chamber 7, which is the interior of the bellows 1. The first housing part 3, guided by the guide element 6, starts to move axially and extends accordingly. Here, as in the embodiment according to FIGS. 6 to 9, a vacuum is created in the upper pressure chamber 7.1, through which the check valve 60 is opened, so that when air is used as the pressure medium, a pressure equalization with the surroundings takes place. If a hydraulic fluid is used as the pressure medium, a pressure-free medium connection with a check valve must be provided at 17.2.

The effective area is no longer the entire cylindrical area of the bellows 1, but the ring area defined by the diameters D1 and D2. Depending on the share of the total pressure area, the initial pressure over the first part of the travel path S1 can correspond to the final pressure, but can also be greater or smaller than the final pressure, since if D1 is adopted as a fixed output variable, D2 can be designed to be variable as required. The effective diameter D1 decreases during the travel path S1, so that the effective area also becomes smaller because the diameter D2 is specified as a fixed size.

However, in order to drive a force-displacement characteristic that approximates the linear force-displacement characteristic of a piston cylinder, or also for other desired control-technical reasons, the force loss typical of the bellows cylinder can be increased during its stroke by increasing the effective area by a further diameter D2 and D3 defined ring area are increased so that the falling force-displacement curve gets a positive boost. Since the travel S2 is larger than the travel S1, the whole thing is repeated again, i.e. The further decreasing diameter D1 and thus the printing area is added a further printing area as compensation, in this example the ring area, defined by the diameters D3 and D4.

If the damping ring 51.2 leaves the bearing housing 8, the entire pressure surface is free. The cylinder now has the same force-displacement characteristics over the rest of its path as an unguided bellows cylinder, but the dimensioning can also be laid out in such a way that the stroke ends when the total pressure area is reached.

After the control device has been switched over, the retracting stroke takes place under the action of external forces. The check valve 60 closes and the pressure medium escapes from the pressure spaces 7 and 7.1 through the channels 21 and 20.1. After opening the first damping ring 51.2 on the bearing housing 8, a separation into the upper pressure chamber 7.1 and the lower pressure chamber 7 again occurs. The external return forces exert a pressure on the pressure medium enclosed in the upper pressure chamber 7.1. The damping rings 51.1 and 51.2 are brought into their lower axial position, so that the pressure medium can reach the rings 51.1 and 51.2 and through the column 26 into the lower pressure chamber 7 and thus to the unpressurized pressure medium supply 17.1 and thus flow away.

In the described embodiment, the undesirable high initial forces are reduced, which, among other things, extends the application possibilities of an actuating device according to the invention. No complex medium transfer pressure control is required in order to obtain an approximately linear force-displacement characteristic, as is present in piston cylinders, in an actuating device according to the invention.

In the described embodiment, with a constant medium pressure, starting from an initial pressure area, additional pressure areas can be switched on, in order to compensate for the decreasing effective area of the bellows cylinder with increasing stroke or to not only compensate for the loss of effective area, but even with the appropriate dimensioning an enlargement. In this way, a pressure force curve can be achieved that begins with low force and increases towards the end of the stroke.

Fig. 11 shows a modified embodiment, in which the falling course of the force during the stroke is counteracted by the fact that the outer surface of the bearing housing 8 and the corresponding inner surface of the housing part recess 3b are each formed in the shape of a truncated parabola in such a way that the loss of the active surface due to the of the stroke-reducing effective diameter is compensated for at every point of the stroke by the parabolic stump tapering upwards. This results in a constant effective force or pressure force over the entire stroke. However, deliberate deviations from this can also be achieved. This is made possible by a seal 61 arranged on the first housing part 3 and acting against the bearing housing 8 to bridge the gap widths that change during operation between the first housing part 3 and the bearing housing 8.

A greatly reduced initial force results if the check valve 60 is installed in the medium supply 17.1 and the medium is supplied at 17.2. Then, when the damping rings 51.1 and 51.2 are arranged or installed in reverse to the arrangement shown in FIG. 10, the active surface between the diameters D3 and D4 (FIG. 10) is first applied. The extension stroke then begins with a low initial force, which increases gradually when S1 is greater than S2. In the case of the embodiment according to FIG. 11 with a truncated parabolic bearing housing 8, there is a stepless enlargement until the bearing housing 8 leaves the damping ring or the damping rings or the sealing ring 61, which also has to be installed vice versa.

With this arrangement, it is also possible to drive an adjusting stroke with a small linear force, in order then to switch on the large effective area or pressure area in a precisely defined manner depending on the path in order to generate a large final pressure.

Instead of the check valve 60 (FIG. 10), a throttle check valve can also be provided. A corresponding adjustment of the throttle causes a gentle start of the extension stroke by only slowly compensating the negative pressure.

Although in the embodiment according to FIG. 11 the bearing housing 8 and the associated housing part recess 3b are formed in the shape of a truncated parabola, a corresponding frustoconical shape could also be provided.

In the embodiment according to FIG. 10, the damping rings 51.1 and 51.2 are each arranged in a groove which is formed in the wall of the recess 3b. In a modified embodiment (not shown), the damping rings are each arranged in a groove in the bearing housing. In a further modified embodiment, the damping ring has a movable sealing lip instead of the axial and radial flow grooves, which blocks the passage of the medium in one direction and releases it in the other direction, so that a non-return function is obtained.

Claims (23)

1. A pressure medium driven actuator, comprising an elastomeric bellows (1), preferably rotationally symmetric, which is sealingly arranged with its axial ends between two housing parts (2, 3), as well as a guide element (6) which passes axially through the interior of the bellows and is connected securely to the first housing part (3) and

is mounted on the second housing part (2) in a guide (9), enabling axial relative movement between said housing part and the said guide element (6); characterised in that:

for achieving inner guidance of the two housing parts (2, 3), a sliding or rolling bearing (9) arranged on the second housing part (2) is provided between the second housing part (2) and the guide element

(6), which bearing is provided with a slip-ring-seal which seals the pressure chamber (7) of the bellows (1), and
the sliding or rolling bearing (9) is constructed such that the guide element (6) is mounted on the second housing part (2) to enable only movement in the axial direction.

2. An actuator according to claim 1, characterised in that:

the guide element is a pin (6) with a circular cross- section, and

the slip-ring-seal (10) is arranged on the pressure chamber side (7).

3. An actuator according to claim 2, characterised in that the guide pin (6) is hollow.

4. An actuator according to any one of the preceding claims characterised in that the guide between the guide element (6) and the second housing part (2) lies within the interior chamber (7) defined by the bellows (Figs. 3 and 4).

5. An actuator according to any one of the preceding claims characterised in that in the interior chamber (7) of the bellows (1) a housing element (11) is provided which reduces the volume of the bellows (Figs. 1 and 2).

6. An actuator according to claim 5 characterised in that the second housing part (2, 3) having the guide (9) is drawn into the interior chamber (7) of the bellows (1), in such manner that the total volume of the bellows is reduced (Fig. 3).

7. An actuator according to any one of the preceding claims characterised in that an axially adjustable stop member (44; 44)-is arranged on the guide element (6) for adjusting the stroke (Fig. 4).

8. An actuator according to any one of the preceding claims characterised in that in the interior chamber of the bellows (1) at least one damping element (18/4) is arranged, which acts between the two housing parts (2, 3), and is preferably realised by an industrial shock absorber (Fig. 4a).

9. An actuator according to any one of the preceding claims characterised in that:

it is double acting,

the returning device is realised likewise by a pressure bellows construction (40),

and the pressure chambers (7, 47) of both bellows (1, 40) are controllable by a distributing valve (46) (Fig. 4).

10. An actuator according to any one of the preceding claims characterised in that both housing parts of the bellows are rigidly coupled for common rotation.

11. An actuator according to any one of the preceding claims characterised in that instead of or additionally to a longitudinal guide arranged in the centre of the actuator, a plurality of longitudinal guides are provided on a diameter at the periphery of the housing parts (2, 3) but passing through the bellows (1

12. An actuator according to any one of claims 1 to 11 characterised in that:

the first housing part (3) has a recess (3a) into which a bearing housing (8) of the second housing part (2), which bearing housing passes through the bellows (1), engages upon relative movement between both housing parts (3, 2), and

a throttle connection (26, 51; 22, 23, 24) is formed between a chamber (7.1) in the recess (3a) of the first housing part (3) above the bearing housing (8), and the inner chamber (7) of the bellows (1) and/or the pressure fluid inlet (17.1, 20.1, 21).

13. An actuator according to claim 12 characterised in that:

the throttle connection is formed between the chamber (7.1) in the recess (3a) of the first housing part (3) above the bearing housing (8) and the inner chamber (7) of the bellows (1), by arranging the bearing housing (8) to have a radial intermediate chamber (26) in the said recess (3a), and by arranging a damping ring (51) in a groove in the wall of the said recess (3a); and

said damping ring has a radial sealing surface (55) in sealing engagement with the bearing housing (8), and is provided with flow-through grooves (52, 53) for the pressure medium on an axial end surface and on the radial outer surface.

14. An actuator according to claim 12 or 13 characterised in that the throttle connection has a passage (22) which is connected with the pressure medium inlet (17.1, 20.1, 21) and via a controllable throttle (23, 25) with a further passage (24), which is formed in the bearing housing (8), and which discharges into the chamber (7.1) in the recess (3a) of the first housing part (3) above the bearing housing (8).

15. An actuator according to any one of claims 12 to 14 characterised in that in the recess (3a) of the first housing part (3) above the bearing housing (8) the chamber (7.1) is in communication with a further pressure medium inlet (17.2).

16. An actuator according to claim 12 characterised in that the bearing housing (8) of the second housing part (2) and the recess (3b) of the first housing part (3) are correspondingly stepped.

17. An actuator according to claim 16 characterised in that:

the bearing housing (8) is axially movable in the recess (3b) of the first housing part in the presence of a split ring (26) between the bearing housing (8) and the recess (3b);

and a damping ring (51.1, 51.2) is arranged in a groove in a wall of each step of the housing part recess and has a radially inner sealing surface (55) in sealing engagement with the outer surface of the bearing housing (8), and has flow-through grooves (52, 53) on an axial end face and on the radial outer surface.

18. An actuator according to claim 16 characterised in that:

the bearing housing (8) is movable axially in the recess (3b) of the first housing part in the presence of a split ring (26) between the bearing housing (8) and recess (3b); and

a damping ring is arranged in a groove of each step of the bearing housing (8), has a radial outer sealing surface in sealing engagement with the wall of the recess (3b), and is provided with flow-through grooves on an axial end surface and on the radial inner surface.

19. An actuator according to claim 17 or 18 characterised in that the damping ring has a movable sealing lip in place of the flow-through grooves, which prevents flow-through of the pressure medium in one direction and allows the flow in the other direction.

20. An actuator according to any one of claims 16 to 19 characterised in that a pressure medium inlet (17.2) is provided, in communication with the chamber (7.1) in the recess (3a) of the first housing part (3) above the bearing housing (8), in which inlet (17.2) a check valve (60) is arranged.

21. An actuator according to claim 20 characterised in that the check valve (60) is formed as a one- way restrictor valve.

22. An actuator according to claim 12 characterised in that the bearing housing (8) and the recess (3b) of the first housing part (3) receiving the bearing housing each have a respective frusto conical and/or truncated parabolic shape.

23. An actuator according to claim 22 characterised by a seal (61) arranged on the first housing part (3) and effective to seal against the bearing housing (8) to bridge over the operatively variable gap widths between the first housing part (3) and the bearing housing (8).

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