EP1847720B1 - Linear actuator - Google Patents

Abstract

The linear drive device (1) has a linear drive (10) with end-position damping by damping devices (35), and two working chambers (12a, 12b). The venting of the downstream working chamber (12a) is controlled through a pressure-limiting valve device (47). Venting takes place only when a preset minimum pressure exists in the downstream working chamber, producing an independent end-position damping effect when required.

Description

The invention relates to a linear drive device, comprising a pneumatic linear drive, which has a drive housing in two working chambers from each other dividing drive unit, which is linearly movable by controlled Druckluftbeaufschlagung starting from at least one starting position in at least one stroke end position, and which is equipped with damping means which during a the achievement of at least one Hubendlage previous damping phase can reduce the Ausströmrate the displaced from the currently downstream working chamber air to decelerate the drive unit.

Such a device is eg in US 3,238,850 disclosed.

One from the DE 20 2005 018 038 U1 known linear drive device of this type includes a pneumatic linear drive, which is equipped with damping means for slowing down the speed of its drive unit. The damping means are operative during a short damping phase which may precede the achievement of one or both stroke end positions of the drive unit. During this damping phase, a downstream of the working chamber associated Abströmquerschnitt is shut off, so that the compressed air only throttled, with a greatly reduced Ausströmrate, can flow to the environment. The backpressure which builds up here in the outflow-side working chamber ensures a reduction in the lifting speed of the drive unit.

The above-described pneumatic damping system is usually designed for the specific application. In particular, the lifting speed of the drive unit is taken into account. At very high stroke speeds, strong throttling is required to effectively decelerate the drive unit, while low drag speeds require only low throttle intensity. Although such different load cases can be taken into account in the aforementioned prior art by a variation of the throttling intensity of the damping channel. However, finding the optimum setting for the particular load case is relatively difficult and time consuming. For applications with frequently changing lifting speeds and / or load cases, such a damping system is therefore not to be fully recommended.

To counteract the described problem, it is not uncommon to make in addition to the damping means downstream of this exhaust air throttling. An adjustable throttle which is switched into the venting flow here fundamentally restricts the venting flow rate in order to limit the stroke speed of the drive unit. Again, however, there are mainly inadequacies when the linear actuator is to be operated with different strokes, in other words, the final end position damping stroke movement begins at different starting positions. The latter is a problem occurring, for example, in the production of PET bottles, where the linear drive device is to be used for the stretch-blow process of the bottle body and different starting positions for the return stroke resulting from the fact that different sized bottle body must be axially stretched to varying degrees. In order to achieve an optimal result in this case with effective cushioning, it has been usually forced to resort to different sized linear drives for different stroke ranges.

It is the object of the present invention to propose measures that allow effective end position damping independently of the stroke of the drive unit.

To solve this problem, the downstream working chamber of the linear drive is connected to existing in addition to the damping means and independently of these working pressure limiting valve means which cause venting of the downstream working chamber only from reaching a prevailing in this downstream working chamber predetermined minimum pressure.

In this way, a highly effective cushioning is ensured regardless of different starting positions of the drive unit without changing the setting of responsible for the cushioning damping means. The pressure conditions in the outflow-side working chamber which are greatly different as a function of the different starting positions and consequently also the resulting different lifting speeds are made uniform by the pressure limiting valve means, so that comparable conditions prevail during the damping phase, with the consequence of a constant damping quality. While, for example, in the case of a pure exhaust air throttling, the pressure prevailing in the downstream working chamber before reaching the damping phase can vary greatly depending on the stroke of the drive unit - the working chamber pressure can either be very high at the beginning of the stroke or, due to a delayed response of the drive unit and an associated strong pressure reduction via the exhaust throttle, be very low - is set by the pressure limiting valve according to the invention largely independent of the stroke and a substantially constant back pressure, so that at the beginning of the damping phase as far as possible same, optimal conditions prevail, regardless of the stroke of the underlying starting position of the drive unit. As long as the prevailing in the downstream working chamber pressure has not reached the predetermined by the pressure limiting valve means minimum pressure, the outflow-side working chamber remains shut off from the environment. Only when the minimum pressure is reached, the pressure limiting valve means release the vent path. As a result, the build-up of excessive back pressure in the downstream working chamber is prevented.

Advantageous developments of the invention will become apparent from the dependent claims.

It is advantageous if the response threshold of the pressure-limiting valve means is adjustable. This allows on-site optimization of the kinematic design with regard to the desired damping intensity and permitted lifting speed.

In principle, it would be possible to detect the reaching of the response threshold of the pressure prevailing in the outflow-side working chamber by pressure-sensing means and to selectively switch it to the open position or the closed position on the basis of one of these generated electrical sensor signal causing the pressure limiting shut-off valve device. Preferably, however, purely mechanically and by pressure force operable pressure limiting valve means are used, so that unnecessary electrical monitoring and control measures. In this case, the pressure limiting valve means expediently comprise a spring-loaded shut-off valve member which is biased counter to the spring force by the outflow-side air pressure, wherein the force-related tuning is such that the shut-off valve member only opens and allows venting of the connected working chamber, if the pending in this working chamber air pressure has reached the predetermined minimum by the spring force. If, for some reason, the accumulating air pressure drops below the minimum pressure again, the shut-off valve member can return to the closed position which prevents the venting.

The spring force which biases the shut-off valve member into the closed position is expediently adjustable.

The channel guidance within the linear drive takes place in particular such that the air displaced by the drive unit flows both outside and during the damping phase into a control channel to which the pressure-limiting valve means are connected or connectable. Passing through this control channel expediently also takes place the pressurization in the connected working chamber when the opposite stroke movement of the drive unit is to be caused.

The linear actuator is suitably associated with a directional default valve means which is connected to the two working chambers and this can alternately connect to a compressed air source or a venting channel to cause the desired lifting movement of the drive unit in one or the other direction. In such a Arrangement, the pressure limiting valve means are suitably turned on in the course of that venting channel, which is connectable by the directional default valve means with that working chamber, which are associated with the damping means.

The two working chambers are assigned in this case expediently separate ventilation channels. If end position damping is desired only in one stroke direction, the venting channel which can be connected to the other working chamber can be connected directly to the environment without intermediate pressure-limiting valve means.

There is also the alternative possibility of connecting a controlchannel connected to the working chamber used for damping purposes to both the pressure-limiting valve means and, in parallel connection, to a non-return valve permitting an inflow of compressed air into the connected working chamber and blocking in the opposite direction. In this case, the supply of compressed air can take place via the non-return valve, which blocks in the opposite flow direction, so that the pressure-limiting valve means are then effective in the described manner.

If the linear drive device is equipped with a directional specification valve device, the pressure limiting valve means and the non-return valve connected in parallel therewith are expediently interposed between the directional presetting valve device and the control channel. However, since the check valve inevitably causes a limitation of the compressed air inflow rate, if possible, the check valve will be dispensed with and the pressure relief valve means as described will be assigned to a venting channel downstream of the directional default valve means.

In a preferred embodiment, the damping means are designed so that they only become effective in the respective stroke direction of the drive unit when the drive unit has approached from its initial position to an attenuation start position to the associated Hubendlage. At this damping start position, the damping phase expediently begins until the stroke end position is reached. Outside the damping phase, the compressed air displaced by the drive unit can flow off via a main channel with a large flow cross-section adjoining the outflow-side working chamber, so that the desired operating speed of the drive unit is ensured. During the damping phase of the main channel is separated by the drive unit from the downstream working chamber, so that the further acted by the moving drive unit compressed air only throttled flow through the throttle channel and can reach the downstream pressure relief valve means. The flow rate of the outflowing compressed air is reduced by the throttle channel, so that a back pressure or dynamic pressure which causes the desired speed reduction of the drive unit can build up in the outflow-side working chamber.

The throttle channel and the main channel are conveniently combined at their side opposite the connected working chamber in a control channel to which the pressure limiting valve means are connected, either directly or preferably with the interposition of a directional default valve device. Across this control channel can then take place expediently, the pressurization for the oppositely directed lifting movement.

Figur 1

in schematischer Darstellung und teils im Längsschnitt eine bevorzugte Bauform der erfindungsgemäßen Linearantriebsvorrichtung, und

Figur 2

einen Ausschnitt der Linearantriebsvorrichtung aus Figur 1 im Bereich modifizierter, mit einem Rückschlagventil kombinierter Druckbegrenzungs-Ventilmittel.

The invention will be explained in more detail with reference to the accompanying drawings. In this show:

FIG. 1

in a schematic representation and partly in longitudinal section a preferred design of the linear drive device according to the invention, and

FIG. 2

a section of the linear drive device FIG. 1 in the area of modified pressure relief valve means combined with a non-return valve.

The designated in its entirety by reference numeral 1 linear drive device includes a pneumatic, that is operated with compressed air linear drive 10, which is aligned vertically in the embodiment described here. However, the linear actuator 10 can also operate with a different orientation.

The linear drive 10 includes an elongated, designated as a drive housing 2 housing, which is composed of an example of a housing tube 3 and two arranged on the end faces housing covers 4a, 4b.

By the drive housing 2, an elongated interior 5 is defined in which a drive piston 6 is slidably received in the direction of the longitudinal axis 7 of the drive housing 2.

The drive piston 6 carries in the region of its outer circumference annular sealing means 8, which are in sealing contact with the peripheral wall of the inner space 5, so that this inner space 5 is divided by the drive piston 6 with sealing in two axially successive working chambers 12a, 12b.

The drive piston 6 is part of a generally designated by reference numeral 13 drive unit which is movable relative to the drive housing 2 in the direction of the longitudinal axis 7 in two opposite directions of lift 14a, 14b. The movement of the drive unit 13 can be tapped outside of the drive housing 2 to perform any application-specific actions.

The linear drive 10 of the embodiment is designed as a pneumatic cylinder. Its drive unit 13 therefore has a piston rod 15 connected to the drive piston 6, which extends coaxially with the longitudinal axis 7 and passes through the housing cover 4b, which is referred to below as the front housing cover, displaceably guided under sealing. Corresponding sealing means and guide means are schematically indicated at 16.

The opposite, in the following the better distinction because of the back cover called other housing cover 4a is closed. However, it would be possible to design the piston rod 15 in such a way that it completely penetrates the drive housing 2 axially and therefore also passes through the rear housing cover 4a.

The two working chambers 12a, 12b are in each case connected to their own control channel 18a, 18b, which passes through the wall of the drive housing 2 and opens out on the outside of this drive housing 2. These control channels 18a, 18b are connected directly or via intermediate fluid lines 22 to a directional default valve device 23, which for example has the functionality of a 5/2-way valve. It is designed for electrical operation, which may be a pilot operated valve device.

In addition to the two working ports 24, 25 connected to the control channels 18a, 18b, the directional default valve device 23 has a feed connection 26 connected or connectable to a compressed air source 31 and two venting ports 27, 28 leading to the atmosphere.

By means of the directional specification valve device 23, the two working chambers 12a, 12b can alternately be subjected to compressed air in opposite directions and vented in order to displace the drive unit 13 by the pressure difference acting on it in one of the two stroke directions 14a, 14b.

The drive unit 13 can be moved between two predetermined by housing fixed stop means 32 axial Hubendlagen. The stop means 32 are, for example, faces of the housing covers 4a, 4b facing the interior 5, onto which the drive unit 13 has accumulated with its drive piston 6 when its stroke end position is reached.

In the retracted stroke end position, the drive piston 6 is located on the rear housing cover 4a and in the extended stroke end position on the front housing cover 4b. The movement of the drive unit 13 in the direction of the retracted stroke end position is referred to as the retraction movement 33a, the movement in the direction of the extended stroke end position as the extension movement 33b.

Depending on the direction of movement, compressed air is fed into one working chamber and at the same time compressed air is removed from the other working chamber. The working chamber currently supplied with compressed air is also referred to below as the inflow-side working chamber, which currently has a venting connection 27 or 28 connected working chamber as a downstream working chamber.

The exemplary embodiment shows an application of the linear drive device in a combined stretch-blow process, which is used in the production of plastic containers, in particular beverage bottles. Preferably, it is the molding of plastic bottles made of PET plastic material.

An output body for a plastic container to be produced is indicated at 17. He is placed in extension of the retracted Hubendlage engaging drive unit 13. Subsequently, the drive unit 13 is driven to its extension movement 33b, wherein it dips into the designed as a hollow body output body 17 and this axially stretches by mechanical loading. Subsequently or simultaneously, pressurized air under high pressure is blown into the outlet body 17 via at least one discharge opening 34 assigned to the piston rod 15, so that the latter presses against the wall of a negative mold receiving it, forming the desired container.

For the extension movement 33b, the retracted stroke end position forms the starting position. Your final position has reached the extending drive unit 13 in the embodiment in the apparent from the drawing intermediate position between the two Hubendlagen, ie before it has arrived in the extended Hubendlage. This end position is determined by the length of the required for the production of the plastic container stretching operation. In conjunction with the production of larger or smaller plastic containers, the end position of the extension movement 33b can also be at a different axial position and maximum with the extended Stroke end position coincide. In any case, the end position reached during the extension movement 33b forms the starting position for the retraction movement 33a completed when the retracted stroke end position is reached. As can be explained, this starting position, as explained, can vary axially in an application-specific manner and, accordingly, also the length ratio present at the starting position and therefore also the volume ratio of the two working chambers 12a, 12b.

The overhead in the illustrated vertical arrangement rear working chamber 12a are associated with the linear drive 10 damping means 35 which cause the drive unit 13 is braked during its retraction 33a during a pre-retracted end position damping phase and consequently with only greatly reduced kinetic energy on the the retracted stroke end position predisposing stop means 32 impacts. This protects the components and reduces operating noise. The retraction movement 33a is thus composed of an initially uninfluenced by the damping means 35 movement phase and a subsequent thereto from a certain damping start position damping phase.

The front working chamber 12b are assigned no comparable damping means in the embodiment. The extension movement 33b therefore takes place undamped throughout. Nevertheless, it is of course possible to additionally allocate damping means 35 to the front working chamber 12b or only to this front working chamber 12b.

The principle of operation of the damping means 35 is fundamentally based on the fact that during the aforementioned damping phase the outflow rate of the air displaced from the momentarily outflow-side working chamber 12a is reduced. Thereby builds in the downstream working chamber 12a on a back pressure, which opposes the retracted stroke end position approximate drive unit 13, a fluidic force that is higher than outside the damping phase. Details of the preferred embodiment of the damping means 35 realized in the embodiment will be explained below.

At the rear working chamber 12a in coaxial extension connects to a main channel 36 forming recess, which is suitably formed in the rear housing cover 4a and is connected via a channel mouth 37 with the rear working chamber 12a in fluid communication. In the region of the channel mouth 37, ie the transition region between the main channel 36 and the rear working chamber 12a, a sealing ring 38 framing the channel mouth 37 is fixed to the housing. The control channel 18a used for the control of the rear working chamber 12a passes through the wall of the rear housing cover 4a and is in constant communication with the main channel 36.

The control channel 18a is also in fluid communication with the rear working chamber 12a via a throttle passage 42 bypassing the main passage 36. The provided by him flow cross-section is substantially less than that of the main channel 36th

In the course of the throttle channel 42 is a schematically indicated in the drawing throttle device 43 is switched on, either predetermines a certain throttling intensity or, suitably, offers an adjustment with respect to the desired throttling intensity. The throttle device 43 may include an adjustable throttle screw.

The drive unit 13 carries on its rear cover facing the rear side 4a as a damper piston markable piston-like closure member 44. This is aligned coaxially with the main channel 36 and can dive into the fixed in the region of the channel mouth 37 sealing ring 38 with sealing, so that the fluid connection between the rear Working chamber 12 a and the main channel 36 is shut off. A fluid connection between the rear working chamber 12 a and the associated rear control channel 18 a is then given only via the throttle passage 42.

In order to cause the retraction movement 33a starting from the illustrated starting position of the drive unit 13, the direction setting valve device 23 is switched so that the front control channel 18b communicates with the compressed air source 31 and the rear control channel 18a with a connected to the one vent port 27 to The drive unit 13 thus moves backwards - in the embodiment upwards - the retraction 33a is initially still undamped because the displaced from the rear working chamber 12a compressed air can flow over the large cross section of the main channel 36. However, as soon as the closure member 44 is immersed in the sealing ring 38 - this marks the damping start position - the compressed air can leave the rear working chamber 12a only throttled over the narrower throttle passage 42 through, so that the lifting movement of the drive unit 13 slows down and the final impact on reaching the retracted stroke end position is tolerable low.

The extension movement 33b is effected by switching the direction setting valve means 23. So that in this case the fed via the rear control channel 18 a of compressed air At the beginning of the possibility, to act on the drive unit 13 with a relatively large volume flow, the sealing ring 38 is formed as part of a non-return valve in the corresponding flow direction. Thus, the injected compressed air can flow not only through the throttle channel 42, but also through the main channel 36 from the beginning to the rear working chamber 12a. The full throughput occurs after the closure member 44 is extended out of the sealing ring 38.

In the course of connectable to the rear working chamber 12a first vent passage 45 pressure relief valve means 47 are turned on. These affect the venting flow rate of the air displaced in the retraction movement 33a, independently of and in addition to the damping means 35. Specifically, they are designed to permit venting of the downstream working chamber 12a to the atmosphere only when in the lock-side cylinder chamber 12a, a predetermined minimum pressure of the compressed air prevails. This minimum pressure practically represents the response threshold of the pressure limiting valve means 47. If the air pressure is lower, take the pressure limiting valve means 47 a the first venting channel 45 completely shut off a closed position. From reaching the minimum pressure and at higher air pressure are the pressure limiting valve means 47 in a venting enabling, that is, the connection between the first vent passage 45 and the atmosphere unlocks open position.

In this way, from the beginning of the retraction movement 33a takes place to a kind of pressure control of the downstream air pressure, that is, a setting and largely constant maintenance of the mentioned minimum pressure. This ensures in the downstream working chamber 12a is independent of the axial starting position of the retraction movement 33a pressure adjustment to a level that ensures the desired end position damping function, in conjunction with a maximum acceptable retraction speed of the drive unit thirteenth

For example, if the home position is relatively far away from the retracted stroke end position, and thus the urging pressure in the front working chamber 12b rapidly builds up at the beginning of the retracting movement 33a, the pressure limiting valve means 47 prevent excessive pressure rise in the rear, downstream working chamber by early opening 12a. Otherwise, this increase in pressure could result in the retracting drive unit 13 not immediately reaching a stable stroke end position, but being excited to oscillate.

If the starting position of the drive unit 13 is relatively close to the retracted stroke end position, it takes longer until the correspondingly larger volume front working chamber 12b has built up the actuation pressure required for the retraction movement 33a. In the case of a construction with an exhaust air throttle which is present instead of the pressure limiting valve means 47, the pressure prevailing in the rear working chamber 12a over the exhaust air throttle could degrade to such an extent during this period that a sufficiently high back pressure can no longer build up in the damping phase. By contrast, the pressure-limiting valve means 47 according to the invention, in this phase, the rear working chamber 12a is completely separated from the atmosphere, so that the disadvantageous pressure reduction can not take place. Consequently, here can be despite one low hub build the required for the functioning of the damping means minimum pressure.

The above explanations also apply to the modified design of FIG. 2 , This differs, on the one hand, in that the pressure-limiting valve means 47 are interposed between the control channel 18a and the directional default valve device 23 (not shown here). In order to allow the supply of compressed air into the control channel 18a, in this case the pressure-limiting valve means 47, a check valve 48 is connected in parallel. The latter allows compressed air flow from the directional default valve device 23 to the control channel 18a, bypassing the pressure limiting valve means 47, but prevents such in the opposite direction, so that then the pressure limiting valve means 47 are effective in the described manner.

Since the check valve 48, the flow rate of the incoming compressed air is restricted compared with an open channel connection, the design of the FIG. 1 that of the FIG. 2 usually preferable. The design of the FIG. 1 allows unthrottled pressurization of the drive unit 13 to cause the extension movement 33b, so that a very high extension speed can be achieved.

In both embodiments, it is advantageous if the response threshold of the pressure-limiting valve means 47 is adjustable. This allows an optimal design of the overall system in terms of damping intensity and lifting speed.

The pressure limiting valve means 47 preferably have a spring-loaded by spring means 52 in a closed position biased shut-off valve member 53. The shut-off valve member 53 is the outflow prevailing working chamber pressure switched, for example directly ( FIG. 2 ) or via a branched admission channel 54 (FIG. FIG. 1 ). The venting process takes place when the working chamber pressure acting on the shut-off valve member 53 corresponds at least to the minimum pressure acting as a threshold. The threshold can be varied by a change in the Federstellkraft the spring means 52 and specified as desired.

The pressure applied to the shut-off valve member 53 of the outflow-side working chamber is not necessarily directly accessible from the relevant working chamber. In the embodiment of FIG. 1 it is tapped in the pressure-limiting valve means 47 to the linear drive 10 upstream channel portion of the first vent passage 45.

The pressure-limiting valve means 47 are combined with the linear drive 2 expediently to form an assembly. The possibly existing directional default valve device 23 is preferably a part of this module. In FIG. 1 a dot-dash line attached to the drive housing 2 control device 55 is indicated, which includes both the directional default valve means 23 and the pressure limiting valve means 47.

The pressure limiting valve means 47 may be mounted directly to the directional default valve means 23 or integrated therein. In a direct attachment, the first vent channel 45 could be applied to the connection area between the associated vent port 27 and the input port of the pressure limiting valve means 47 may be reduced.

Claims (14)

1. Linear drive device with a pneumatic linear drive (10), with a drive unit (13) dividing two operating chambers (12a, 12b) from one another in a drive housing (2) and capable of linear movement through controlled compressed air pressurisation from one or more starting positions into one or more end-of-stroke positions, and which is equipped with damping means (35) which during a damping phase preceding the reaching of at least one end-of-stroke position are able to lower the rate of outflow of the air forced out of the current outflow-side operating chamber (12a) in order to brake the drive unit (13), characterised in that the outflow-side operating chamber (12a) is connected to pressure limiting valve means (47), additional to and operating independently of the damping means (35), and able to generate venting of the outflow-side operating chamber (12a) only after a predetermined minimum pressure prevailing in this outflow-side operating chamber (12a) has been reached.
2. Linear drive device according to claim 1, characterised in that the response threshold of the pressure limiting valve means (47) is adjustable.
3. Linear drive device according to any of claims 1 or 2, characterised in that the pressure limiting valve means (47) contain an isolating valve element (53), biased by spring loading in a closed position, which only open and allow venting of the outflow-side operating chamber (12a) when the air pressure building up in this outflow-side operating chamber (12a) has reached the minimum pressure preset by the spring adjusting force.
4. Linear drive device according to claim 3, characterised in that the spring adjusting force preloading the isolating valve element (53) in the closed position is adjustable.
5. Linear drive device according to any of claims 1 to 4, characterised in that the pressure limiting valve means (47) are combined with the linear drive (10) to form a unit.
6. Linear drive device according to any of claims 1 to 5, characterised in that the air forced from the drive unit (13) not only during but also outside the damping phase flows into a control passage (18a) to which the pressure limiting valve means (47) are connected.
7. Linear drive device according to any of claims 1 to 6, characterised by a direction setting valve unit (23) controlling the compressed air pressurisation of the two operating chambers (12a, 12b) and therefore the direction of movement of the drive unit (13).
8. Linear drive device according to claim 7, characterised in that the direction setting valve unit (23) is combined with the linear drive (10) to form a unit.
9. Linear drive device according to claim 7 or 8, characterised in that the direction setting valve unit (23) is able to connect at least one vent passage (45) to one of the operating chambers (12a), with the pressure limiting valve means (47) being connected into the course of this vent passage (45).
10. Linear drive device according to any of claims 1 to 9, characterised in that the pressure limiting valve means (47) are connected in parallel to a non-return valve (48) which allows compressed air to flow into the assigned operating chamber (12a) and prevents it from flowing in the opposite direction.
11. Linear drive device according to any of claims 1 to 10, characterised in that the damping means (35) are so designed that they are effective in the relevant direction of stroke of the drive unit (13), when the drive unit (13) moving from its starting position has approached the damping starting position at the assigned end-of-stroke position wherein the drive unit (13), after reaching the damping starting position and during the damping phase which then commences, separates from the outflow-side operating chamber (12a) a main passage (36), which up to that point has been connected with the outflow-side operating chamber (12a), so that the forced air is able to reach the pressure limiting valve means (47) only via a restrictor passage (42) bypassing the main passage (36).
12. Linear drive device according to claim 11 characterised in that there is provided, in the transition zone between the outflow-side operating chamber (12a) and the main passage (36) assigned to it, a seal ring (38) fixed to the housing into which a piston-like sealing element (44) of the drive unit (13) dips with sealing during the damping phase, in order to block the fluidic connection between the operating chamber (12a) and the main passage (36).
13. Linear drive device according to claim 11 or 12, characterised in that an adjustable restrictor device (43) is inserted into the course of the restrictor passage (42).
14. Linear drive device according to any of claims 1 to 13 for use in a stretch blow moulding process in the production of plastic containers, in particular plastic drinks bottles.

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