EP1998054B1 - Pneumatic cylinder with self-adjusting cushioning at the end of stroke and corresponding method - Google Patents

Description

The invention relates to a pneumatic cylinder with a self-adjusting end position damping with a cylinder housing in which a movable cylinder piston is arranged, which is acted upon by a working pressure (p ₁ ) on one side and by the movement of the cylinder piston in the region of the end position of the cylinder piston one of the not pressurized side of the cylinder piston forms limited damping volume, wherein the end position damping comprises a displacement which is limited by a movable therein lifting element and a part of the pneumatic cylinder, and wherein the lifting element on its one side via a damping channel of the pending in the damping vapor pressure (p ₂ ) is acted upon and provided by the lifting element in response to the damping pressure (p ₂ ) openable venting channel and a method for self-adjusting end position damping.

In hydraulic or pneumatic cylinders, an end cushioning is often used to prevent the piston in the final position against the cylinder housing or against a stop beats, the aim of the end position damping is therefore, the speed of a moving mass (piston + load), the center of gravity usually located in the cylinder axis, to a level too in which neither the cylinder nor the machine in which the cylinder is installed is damaged or affected by shocks introduced.

A pneumatic cylinder with the features mentioned is of the generic type US 3,933,080 A known. Here, the cylinder piston is stepped at its associated end and moves at the end of its cylinder stroke with the protruding step in a recess formed in the end wall of the cylinder housing. In this way, two damping volumes are formed in the known pneumatic cylinder, namely a first, by the retracting stage of the cylinder piston in the recess of the housing end wall closed Dämpfvolurnen, and a second, formed in the interior of the cylinder housing between the end wall and the opposite end face of the cylinder piston damping volume. As far as an approach of the cylinder piston to the end wall of the cylinder housing in both Dämpfvolumina a movement of the cylinder piston decelerating damping pressure builds up, each a valve-controlled discharge of each of the two Dämpfvolumina is provided to the atmosphere. In this case, an exemplary embodiment provides a common relief control of the two damping volumes via a lifting element arranged movably in a displacement, wherein a connection between the first damping volume and an outlet opening on one side of the lifting element and a connection between the second damping volume and on the other side of the lifting element Outlet opening exists. By this pressure-controlled cushioning intended to be prevented by a possibly excessive damping pressure rebounding of the cylinder piston during the damping process.

From the DE 295 17 364 U1 is a cushioning in a pneumatic cylinder known in which the resulting at the end of the piston stroke between the front-side cylinder wall and the cylinder piston damping volume is relieved via a connected damper channel to the atmosphere.

In the damper channel, a throttle or a pressure relief valve is turned on, which provide for the construction of a corresponding vapor pressure. Thus, when reaching the Kolbenendlage no overpressure prevails in the formed damping volume, so that the piston could experience a reversal of motion, in addition, a vent valve is provided, which is path-dependent and mechanically switched by the cylinder piston.

Furthermore, path-dependent Endiagendämpfungen are known, such as from the EP 949 422 A1 , which can change an exhaust air cross-section as a function of the piston position and thus can specify a progressive damping curve. However, this Dämpfverlauf is dependent on the fixed geometry and can thus be optimal only for a certain combination of mass and speed. If the pneumatic cylinder is operated away from the optimum operating point, eg when the working pressure (and thus the speed) changes or when another load is moved, the damping is no longer optimal. But this is exactly the case in practice, as it has been shown that the positions at which the pressure peaks occur depending on the load and speed are unterschledlich.

Also pneumatic shock absorbers are known, for example from the DE 37 40 669 A1 , with an outlet valve, over which the air compressed during a damping movement of the piston is discharged. For this purpose, a valve tappet is biased by the working pressure and a spring force. When the pressure of the compressed air exceeds the preload, the exhaust valve opens abruptly and the compressed air is released through a throttle. In order to operate such a shock absorber optimally, a scheme is provided with which the form, against which the piston is moved. Depending on the position of the piston is regulated. With such a scheme, a self-adjusting damping can be achieved, but only at great expense for the scheme.

The objective of the present invention has the object to provide a cushioning of a pneumatic cylinder, and an associated method, which automatically adjusts to different operating parameters, such as mass, speed and working pressure to Erzlelen in a wide range optimal damping and the simple and inexpensive designed.

This object is achieved in that the displacement on the opposite side of the lifting element via a connecting channel with the pressure of the working pressure (p ₁ ) side of the cylinder piston or a voltage applied in an outlet vent pressure (p ₃ ) is connected and in the connecting channel in front of the displacement a check valve is arranged which blocks in the direction of the working pressure (p ₁ ) or the venting pressure (p ₃ ), so that the lifting element the outflow cross section of the venting passage in dependence on the ratio of acting on its one side damping pressure (p ₂ ) to the each on its opposite side in the displacement trapped working pressure (p ₁ ) or venting pressure (p ₃ ) releases. The method according to the invention results accordingly in that the lifting element is moved by the damping pressure (p ₂ ) acting on it against a closed pressure medium volume charged with the working pressure (p ₁ ) or a venting pressure (p ₃ ), so that the lifting element has the outflow cross section of the Venting channels depending on the ratio of the acting on its one side damping pressure (p ₂ ) to each pending on its opposite side in the displacement working pressure (p ₁ ) or venting pressure (p ₃ ) releases.

By this arrangement or this method arises in the displacement of an adaptive gas spring with a progressive spring stiffness, which is dependent on the working pressure or the venting pressure and the pressure in Endlagendämpfraum. As a result, the effective outflow cross section is opened in sections, whereby a nearly linear opening function is present. The spring constant of this gas spring changes independently depending on the prevailing pressures and it is achieved a constant damping effect even at different operating pressures and different kinetic energies. Advantageously, the venting pressure is used in the adaptive gas spring, since the pressure profile on the vent side shows a more pronounced dependence on the travel speed of the cylinder piston and is thus better suited as a controlled variable. The This invention increases the comfort, reliability and ease of use of the pneumatic drive. The automatic adjustment of the end position damping to the operating conditions also eliminates the costs for manual adjustment and the cycle times are reduced.

The vapor volume is advantageously formed by a damping pin extending in the axial direction into the cylinder housing being arranged in the region of the end stop of the cylinder piston, and the cylinder piston being designed with a recess which is acceptable for the damping pin. Characterized the cylinder volume is divided when retracting the damping pin in the recess for forming the damping volume. Alternatively, the damping volume may also be formed by arranging an exhaust duct laterally on the cylinder housing and axially spaced from the cylinder cover.

In a preferred embodiment, the lifting element is designed as guided in the displacement mounted damping piston. The cubic capacity or the damping piston can be arranged, depending on the constructive Ausgesteitung, either in a pneumatic cylinder final cylinder cover or cylinder liners.

Alternatively, the lifting element may also be a sealing element between the damping pin and the cylinder piston, wherein the sealing element is hollow and is arranged in the cylinder piston. With such an arrangement, the number of required end-of-line vapor deposition components can be reduced.

In order to avoid or reduce possible swinging of the cylinder piston when driving onto the volume of air trapped in the damping volume, a vent opening may be provided on the pneumatic cylinder which is connected to the damping volume.

• Flg. 1 einen bekannten kolbenstangenlosen Pneumatikzylinder,
• Fig. 2 eine Ausführung der Erfindung mit der Endlagendämpfung im Zylinderdeckel,
• Fig. 3 eine Ausführung der Erfindung mit der Endlagendämpfung Im Zylinderkolben,
• Fig. 4 eine Ausführung der Endlagendämpfung als Dämpfdichtung und
• Fig. 5 eine Ausführung der Erfindung mit Druckversorgung der adaptiven Gasfeder von der Entlüftungsseite.

The subject invention will be described below with reference to the schematic, non-limiting, preferred embodiments of the invention FIGS. 1 to 4 described. It shows

• Flg. 1 a known rodless pneumatic cylinder,
• Fig. 2 an embodiment of the invention with the end position damping in the cylinder cover,
• Fig. 3 an embodiment of the invention with the end position damping in the cylinder piston,
• Fig. 4 an embodiment of the end position damping as a damping seal and
• Fig. 5 an embodiment of the invention with pressure supply of the adaptive gas spring from the vent side.

In a known end position damping after Fig. 1 At the end of the working stroke, in the region of the end stop of the cylinder piston 22, a damping pin 18 is guided through a damping seal 21 in a recess 23 of the cylinder piston 22 (indicated by dashed lines), whereby an additional chamber is created in the non-pressurized cylinder side - the damping volume 19. The now resulting damping volume 19 can escape only via an intended, not shown here, valve needle, for example in the cylinder cover 4. When retracting the cylinder piston 22, the air that collects in this chamber, compressed and passed by the movement of the piston to the valve needle. However, the volume can not be dissipated in the same time that the piston retracts, which is why a pressure increase occurs in this chamber. The piston is decelerated by this pressure and should therefore not hit the cylinder cover or an end stop, but slowly retract with the time-delayed escape of air. The valve needle is set during commissioning of the cylinder. This form of end position damping can be found in many pneumatic or hydraulic cylinders which have a cushioning, such as in a rodless pneumatic cylinder 1 as in Fig. 1 shown.

In Fig. 2 is an end, here the completed by the cylinder cover 4 end of a pneumatic cylinder 1, here for example a rodless pneumatic cylinder, shown with a self-adjusting end position damping according to the invention in detail. The cylinder piston 22 is, for example, a slide connected to a mass m, and moves under pressure on one side p ₁ at a speed v In a cylinder housing 15 in the direction of the mechanical end stop (in the region of the cylinder cover 4). The cylinder piston 22 is sealed relative to the cylinder housing in a known manner by means of sealing elements 20. The direction of movement is In Fig. 2 indicated by the arrow. The displaced by the movement of air on the non-pressurized side of the cylinder piston 22 is discharged via a channel 3 in the cylinder cover 4 and a connection not shown here.

In the cylinder piston 22, a recess 23 is provided which can receive a axially extending into the cylinder housing 15 Dämpfzapfen 18. The damping pin 18 is arranged in this example on the cylinder cover 4 and in the end region or in the region of an end position of the cylinder piston 22 of the pneumatic cylinder 1, resulting in a Dämpfbereich. An outlet channel 3 extends here in the axial direction through the cylinder cover 4 and through the damping pin 18. Of course, such a damping volume 19 can also be formed differently, in particular without damping pin 18, for example by the outlet channel 3 being laterally spaced from the cylinder cover 4 in the axial direction is arranged on the cylinder housing 15, as in Flg. 2 indicated by dashed lines and indicated by reference numeral 3a. As a result, the outlet channel 3a is closed during the movement of the cylinder piston 22, resulting in the end position of the cylinder piston 22 between the cylinder cover 4 and cylinder piston 22 again a corresponding damping volume 19.

In the cylinder cover 4, a displacement 9 is provided - here a simple bore, which is closed by a disc 10. The displacement 9 is limited by a lifting element, here a damper piston 7, the movable (as indicated by the double arrow in Fig. 2 indicated) and guided in the displacement 9 is arranged. The displacement 9 is connected here via a channel 11 in the cylinder cover 4 and a cylinder housing 15 arranged in the connecting channel 14 with the working pressure p ₁ on the pressurized side of the cylinder piston 22. In the connecting channel 14 or alternatively as in this example in the channel 11 in the cylinder cover 4, a check valve 12 is arranged that blocks in the direction of the working pressure p ₁ . The damping piston 7 is therefore pressurized on one side by the force acting in the displacement 9 working pressure p ₁ . The opposite side 6 of the damper piston 7 is executed stepped in this example and is connected via a damping channel 16 with the damping volume 19. The damper piston 7 closes a venting channel 5 arranged in the cylinder cover 4 and connected to the outlet duct 3. The damper piston 7 may be provided for sealing against the cylinder cover 4 with throttling grooves 8. Instead of throttling grooves 8 but also any other sealing elements may be provided. In order to adjust the new working pressure p ₁ in the displacement 9 at a change in working pressure from one stroke to the next, a targeted leakage can be provided via the throttling grooves 8 or the other sealing elements at this point for pressure reduction in the displacement 9. Likewise, however, it is of course conceivable to vent the displacement 9 between two strokes, if necessary via other suitable means, such as a valve or throttle, or to pressurize it with the new working pressure p ₁ .

Of course, such end position damping can also be provided on the other side of the pneumatic cylinder, so that the opposite movement is endlagengedämpft accordingly. For this purpose, the same arrangement can also be provided on the other side and the working pressure then acting is supplied via the second connecting channel 2 to the second displacement 9.

In the following, the function of the end position damping according to the invention will now be described.

mit A_K der Fläche des Dämpfkolbens, V dem eingeschlossenen Volumen, das von den wirkenden Drücken abhängig ist, und E_L, dem Elastizitätsmodul der Luft, der sich ergibt aus P*n, dem Druck multipliziert mit dem Polytropenexponent. Diese adaptive Gasfeder wirkt dem Hub des Dämpfelements 7 entgegen, wodurch der Abströmquerschnitt nicht schlagartig, sondern progressiv und in Abhängigkeit vom herrschenden Arbeitsdruck p₁ geöffnet wird. Dabei verhält sich die Öffnungsfunktion annähernd linear zum Druck. Die Federkonstante dieser Gasfeder wird durch das Volumen und den Druck des Luftvolumens bestimmt. Wird der Arbeitsdruck variiert, ändert sich damit auch die Federkonstante der Gasfeder. Ändert sich die kinetische Energie des Zylinderkolbens 22, z.B. durch eine höhere Geschwindigkeit v oder eine andere Masse m, passt sich über unterschiedliche Druckverhältnisse der Hub des Dämpfelementes 7 und damit auch das Dämpfverhalten selbstständig an die neuen Gegebenheiten an. Dies funktioniert in einem gewissen Energiebereich, wobei die maximale Dämpfenergie nicht überschritten werden darf. Bei unterschiedlichen Arbeitsdrücken verschiebt sich die Kennlinie der Dämpffunktion.During the movement of the cylinder piston 22, the displaced air is discharged through the outlet channel 3 on the side of the cylinder piston 22 facing away from the pressurized side. The outlet channel 3 is advantageously dimensioned so that the entire displaced air without backflow (and thus without associated pressure increase) can be dissipated. When the cylinder piston 22 ascends in the region of the end position of the cylinder piston 22 by the movement on the damping pin 18, this is guided by a arranged in the recess 23 of the cylinder piston 22 damping seal 21, whereby the cylinder space is divided by the damping seal 21. This creates at the end of the movement of the Cylinder piston 22 a sealed chamber - the damping volume 19, in which the air remaining therein for damping the cylinder piston 22 is compressed by the movement thereof. This damping pressure p ₂ in the damping volume 19 acts via the damping channel 16 on the side 6 of the damping piston 7, the displacement of which 9 facing side is acted upon simultaneously via the connecting channel 14 with the working pressure p ₁ . If the damping pressure p ₂ in the damping volume 19 exceeds the working pressure p ₁ due to the further movement of the cylinder piston 22, the damping piston 7 is raised, as a result of which the air in the displacement 9 is compressed, because the air is prevented from flowing back through the check valve 12. By the stroke of the damping piston 7, the venting channel 5 is opened and the air trapped in the damping volume 19 begins to flow away via the damping channel 16, the venting channel 5 and the outflow channel 3. Due to the trapped in the displacement 9 air volume in the displacement 9, a gas spring with a progressive spring stiffness
$C_L=\frac{{A_K}^2}{V}{e}_L.$

with A _K the area of the damping piston, V the trapped volume which is dependent on the acting pressures, and E _L , the modulus of elasticity of the air resulting from P * n, the pressure multiplied by the polytropic exponent. This adaptive gas spring counteracts the stroke of the damping element 7, whereby the outflow cross section is opened not abruptly, but progressively and in dependence on the prevailing working pressure p ₁ . The opening function behaves almost linearly to the pressure. The spring constant of this gas spring is determined by the volume and pressure of the air volume. If the working pressure varies, so does the spring constant of the gas spring changes. Changes the kinetic energy of the cylinder piston 22, for example by a higher speed v or another mass m, adapts itself to the new conditions via different pressure conditions of the stroke of the damping element 7 and thus also the damping behavior. This works in a certain energy range, whereby the maximum damping energy must not be exceeded. At different working pressures, the characteristic of the damping function shifts.

If the opening pressure in the damping chamber 19 is not reached, for example due to very low speeds when transporting very small masses, there is a risk of oscillation. The oscillation is caused by the driving up of the cylinder piston 22 on the air cushion, which is formed in the damping chamber 19, since the trapped air can not escape. This oscillation can be counteracted, for example, by deliberately introducing one (or more) vent opening (s) 17, for example in the damping journal 18 or in the cylinder housing 15. The vent 17 can be adjusted in its shape, location and size the circumstances, such as the structural design or the expected kinetic energies.

In Fig. 3 an alternative embodiment of a self-adjusting end position damping according to the invention is shown. In this embodiment, the displacement 9 in the cylinder piston 22 is arranged, as well as the connecting channel 14, the check valve 12, the damping channel 16 and the venting channel 5. Otherwise, the function of this cushioning is identical to that with reference to Fig. 2 described.

Fig. 4 shows a further possible embodiment of the invention. In this example, the lifting element is designed as an elastic damping seal 24. The damping seal 24 is arranged on the recess 23 of the cylinder piston 22. The damping seal 24 is hollow and thus forms a volume between the cylinder piston 22 and the damper seal - the displacement 9. When driving the cylinder piston 22 on the damper pin 18 divides the damping seal 24 again the cylinder volume, which again the damping volume 19 is formed. Due to the further movement of the cylinder piston 22 and the associated pressure increase in the damping chamber 19, the damping seal 24 is compressed, as in Fig. 4 indicated by dashed lines. As a result, the damping seal 24 lifts off from the damping pin 18 and creates an annular venting channel 5 between the damping seal 24 and the damping pin 18, through which the air trapped in the damping volume 19 can flow out again. In the displacement 9 is formed by the pressure load by the working pressure p ₁ again a gas spring with progressive spring constant, which counteracts the compression of the damping seal 24. The function of this embodiment is therefore again identical to that with reference to Fig. 2 described.

In the above embodiments, the displacement 9 is always acted upon by the working pressure p ₁ . But it is also conceivable to apply the displacement 9 and the adaptive gas spring from the vent side, as follows based on the Fig. 5 is described. Due to the usual exhaust throttling for regulating the speed of the cylinder piston 22, a back pressure p _{3 is} present on the vent side, whose level is lower than that of the ventilation side. The displacement 9 is connected in this embodiment via a connecting channel 14 and a channel 11 with the outlet channel 3, in which the venting pressure p ₃ is applied. In the connecting channel 14 and in the channel 11, in turn, a check valve 12 is arranged that blocks p ₃ in the direction of the venting pressure. To compensate for the now lower pressure in the displacement 9 of the adaptive gas spring, the lifting element, here again a damping piston 7, can be designed with piston surfaces of different sizes. Until the cylinder piston 22 ascends with the damping seal 21 onto the damping pin 18, the pressure p ₂ in the damping volume 19 and the venting pressure p ₃ in the outlet channel 3 are the same. The venting pressure p ₃ is via the connecting channel 14, the check valve 12 and the channel 11 in the displacement 9 at. If the damping seal 21 closes off the damping volume 19, the venting pressure p ₃ in the outlet channel 3 drops sharply. In displacement 9, however, this pressure is maintained due to the check valve 12. On the damping piston 7 is on page 6 is again the increasing pressure p ₂ in the damping volume 19 and on the other side of the damping piston 7, the venting pressure p ₃ before Dämpfbeginn. Otherwise, the function of this cushioning is identical to that with reference to Fig. 2 described, wherein the adaptive gas spring is now dependent on the venting pressure p ₃ .

Of course, the adaptive gas springs of Endlagendämpfungen according to the embodiments of the Figures 3 and 4 as described above also from the vent side, ie by the venting pressure p ₃ , are applied.

Although the above examples have been described with air as a pressure medium, it is of course also possible to use any other suitable gas as a pressure medium instead of air.

Claims (10)

1. A pneumatic cylinder having a self-adjusting end position damping system having a cylinder housing (15), in which a movable cylinder piston (22) is arranged, which is loaded on one side by a working pressure (p₁), and a damping volume (19), which is delimited by the non-pressure-loaded side of the cylinder piston (22), is formed by the movement of the cylinder piston (22) in the region of the end position of the cylinder piston (22), wherein the end position damping system comprises a stroke space (9), which is delimited by a stroke element (7, 24) that is movable therein and a part of the pneumatic cylinder (1), and wherein the stroke element (7, 24) is loaded on one side by the damping pressure (p₂) present in the damping volume (19) via a damping duct (16), and a ventilation duct (5) is provided, which can be opened by the stroke element (7, 24) depending on the damping pressure (p₂),
   characterised in that
   the stroke space (9) on the opposite side of the stroke element (7, 24) is connected via a connection duct (14) to the side of the cylinder piston (22) that is pressure-loaded by the working pressure (p₁) or a ventilation pressure (p₃) present in an outlet duct (3), and a check valve (12) is arranged in the connection duct (14) upstream of the stroke space (9), which check valve blocks in the direction of the working pressure (p₁) or the ventilation pressure (p₃), so that the stroke element (7, 24) opens the outflow cross section of the ventilation duct (5) depending on the ratio of the damping pressure (p₂) effective on its one side to the working pressure (p₁) or ventilation pressure (p₃) enclosed in the stroke space (9) on its opposite side.
2. The pneumatic cylinder according to claim 1,
   characterised in that
   a damping bolt (18), which extends into the cylinder housing (15) in the axial direction, is arranged in the region of the end stop of the cylinder piston (22), and the cylinder piston (22) is configured with a recess (23), which receives the damping bolt (18).
3. The pneumatic cylinder according to claim 1,
   characterised in that
   the outlet duct (3) is arranged laterally on the cylinder housing (15) and at an axial distance from a cylinder cover (4).
4. The pneumatic cylinder according to any one of claims 1 to 3,
   characterised in that
   the stroke element is configured as a damping piston (7), which is mounted such that it is guided in the stroke space (9).
5. The pneumatic cylinder according to claim 4,
   characterised in that
   the stroke space (9) is arranged in a cylinder cover (4), which closes off the pneumatic cylinder (1).
6. The pneumatic cylinder according to claim 4,
   characterised in that
   the stroke space (9) is arranged in the cylinder piston (22).
7. The pneumatic cylinder according to claim 2,
   characterised in that
   an elastic sealing element (24) is provided as the stroke element between the damping bolt (18) and the cylinder piston (22), wherein the sealing element (24) is hollow and is arranged in the cylinder piston (22).
8. The pneumatic cylinder according to any one of claims 1 to 7,
   characterised in that
   a ventilation opening (17), which is connected to the damping volume (19), is provided on the pneumatic cylinder (1).
9. The pneumatic cylinder according to any one of claims 1 to 8,
   characterised in that
   a self-adjusting end position damping system is arranged at both end positions of the cylinder piston (22).
10. A method for self-adjusting end position damping of a cylinder piston (22) of a pneumatic cylinder (1), which is moved in a cylinder housing (15) and is loaded on one side by a working pressure (p₁), and wherein a damping volume (19), which is delimited by the non-pressure-loaded side of the cylinder piston (22), is formed by the movement of the cylinder piston (22) in the region of the end position of the cylinder piston (22), wherein a damping pressure (p₂) is produced in the damping volume (19) by the movement of the cylinder piston (22), with which a stroke element (7, 24) is loaded, by means of the movement of which a ventilation duct (5) is opened for the damping pressure (p₂),
    characterised in that
    the stroke element (7, 24) is moved by the damping pressure (p₂) loading said stroke element against a closed off pressure medium volume, which is loaded with the working pressure (p₁) or a ventilation pressure (p₃), so that the stroke element (7, 24) opens the outflow cross section of the ventilation duct (5) depending on the ratio of the damping pressure (p₂) effective on its one side to the working pressure (p₁) or ventilation pressure (p₃) present on its opposite side in the stroke space (9).

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