DE9320952U1 - Flow valve - Google Patents

Description

The invention relates to a vacuum clamping device for a flow valve for machine tables of woodworking machines with several support beams on which at least one workpiece support is movably arranged, wherein each support beam is equipped with several flow valves and each flow valve has a valve housing in which a flow channel is provided, wherein a movable valve part is arranged in the flow channel, which rests against a valve seat when a predetermined pressure difference is present and closes the flow channel, wherein a flow path is provided which bypasses the sealing point between the movable valve part and the valve seat, wherein the flow resistance is significantly greater than the flow resistance of the open valve.

Postbank Stuttgart 50771-705 (bank code 600 100 70) · Dresdner Bank Stuttgart 1919 854 00 (bank code 600 800 00) S.W.I.F.T.-adress DRES DE FF

A large number of flow valves are known. For example, DE 34 29 444 A1 discloses a vacuum valve for suction bars, which is used to lift and transfer flat objects. This valve has a flow channel in which a ball is arranged as a valve part. If the flow valve is placed on a flat valve part via a suction gripper, the air in the space between the flow valve and the flat object is sucked out by applying a vacuum. In this way, large holding forces can be generated and the flat object can be lifted and transported via the flow valve. If the flow valve is open to the atmosphere, the ball closes the flow channel so that the vacuum at the suction connection does not collapse. In order to be able to vacuum the space between the flow valve and the object when the valve is closed, the flow valve has a bypass channel that connects the suction connection with the space between the flow valve and the object. It has been found to be disadvantageous that the suction of the air from the space is very time-consuming, since the flow resistance of the bypass channel is significantly greater than the flow resistance of the open valve. It has also been shown that when very porous objects are vacuumed in the space, no vacuum can be built up, since the porous

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material of the object, the extracted air immediately flows back in.

DE 88 15 392 Ul has introduced a flow valve in which the valve part located in the flow channel is lifted off the valve seat in the resting position. If there is a small differential pressure on both sides of the valve part, the valve part remains lifted off and a large volume flow can be sucked off. From a certain differential pressure, the valve part is carried along and rests on the valve seat, thereby closing the flow channel. Suction can now only take place via a bypass channel, which, however, has a much greater flow resistance than the open valve. With such a flow valve, closed-pore objects can be sucked in relatively quickly, but with open-pore objects the problem also arises that the valve part is pressed into the valve seat due to the high flow rate and the air can only be sucked off via the bypass channel.

DE 41 01 248 A1 discloses a flow valve which has a bypass whose flow resistance is adjustable. With such a flow valve, the lifting device can be adjusted to the porosity of the object so that, according to the

Setting means that both closed and open-pored objects can be sucked in equally well. If the flow resistance of the bypass is reduced, then porous objects can be sucked in well, but this increases the leakage air flow when the flow valves are not in contact with the object, i.e. when the flow valves are open to the atmosphere.

In addition, woodworking machines are generally known that have clamping tables on which workpieces, e.g. wooden panels, can be clamped using negative pressure. For this purpose, several support beams are arranged on the clamping table, in which two negative pressure-carrying devices, e.g. channels, are provided. These channels extend over the length of the support beam and the flow valves can be connected to these channels.

Based on the object mentioned at the outset, the invention is based on the object of providing a further developed vacuum clamping device.

The object is achieved according to the invention in that the flow valve has a second flow channel, that a second movable valve part is arranged in the second flow channel and that the second movable valve part opens the second flow channel depending on the

Flow direction in front of the valve seat of the first flow channel opens or closes the pressure.

In addition to the already known flow channel with the movable valve part arranged therein, which opens or closes the flow channel, the flow valve according to the invention has a further flow channel that can be closed using a second valve part. This second valve part reacts to the pressure prevailing in the first flow channel and, depending on this pressure, opens the second flow channel or keeps it closed. If a suction gripper is equipped with such a flow valve and the suction gripper is placed on an object to be lifted, the air is sucked out of the space between the flow valve and the object via the first flow channel. The pressure gradually decreases in the direction of flow in front of the valve seat. Once it has reached a certain value, the valve part located in the second flow channel is moved from its rest position, in which it closes the second flow channel, thereby opening this second flow channel. If this second flow channel is also under vacuum, additional air is sucked out of the space between the flow valve and the object via the second flow channel. By adding the second flow channel to the first flow channel, the volume flow is increased considerably. In this way,

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porous objects can also be sucked in without the bypass or the flow path bypassing the valve seat in the first flow channel having to be enlarged. The second valve is controlled by the pressure or differential pressure in the first flow channel. This pressure or differential pressure can be adjusted to specific objects to be sucked in, so that the second valve part opens, for example, even at a low differential pressure, which is usually the case with porous objects. The differential pressure here is understood to be the pressure difference before and after the first valve part.

In an advantageous further development, it is provided that the pressure prevailing in the second flow channel and the pressure prevailing in the first flow channel are present on the second valve part. These pressures form a second differential pressure. This second valve part can be pushed into the working position or rest position either by differential pressures or by different sized surfaces on the valve part.

Preferably, the flow valve has one or two flow inlets and one or two flow outlets. It can therefore be connected to a single vacuum pump or it can be connected to a single suction gripper. The first flow channel serves only as

Control channel for the second valve part of the second flow channel.

In one embodiment, the second valve part is in its rest position when it closes the second flow channel. Only in its working position does the second valve part open the second flow channel, through which additional air can then be sucked out.

The second valve part is preferably designed as a movable piston. Using suitable bearings and tolerances or inserts and sealing means, the piston can be moved in its bore with little effort, while the piston seals the second flow channel to such an extent that leakage losses are negligible.

In another embodiment, the piston is designed as a stepped piston with different sized effective areas (piston areas). In this way, the switching characteristics of this second valve part can be changed and adapted to specific applications, e.g. early opening and late closing.

In a further embodiment, the second valve part is designed as a membrane. A membrane has the advantage that no sliding parts are necessary and therefore

no frictional forces have to be overcome and the adjustment paths are extremely short. Such flow valves react extremely quickly. Here too, differential areas are possible, so that different switching functions can be achieved in this way.

In embodiments, the force of a spring is applied to the second valve part in at least one adjustment direction. The use of springs to support the adjustment movement of the valve part has the advantage that the switching function can be influenced in a targeted manner or the flow valve can be adjusted to certain pressure differences. Due to the possibility of the second valve part being arranged in an exchangeable manner in the valve housing, the flow valve can be adjusted precisely to the desired purpose, e.g. for certain objects, by using other valve parts. Maintenance work is also much easier to carry out.

In another embodiment, the opening or closing pressure for the second valve part is adjustable. This can be done, for example, by pre-tensioning a spring or by changing the pre-tension of the spring or by using pistons, membranes or other valve parts with different effective areas for the two pressures in the two flow channels.

In design variants of the flow valve, it is provided that the first valve part is loaded by the force of a spring in the opening direction. If flow valves are used in which no spring acts on the first valve part, then such flow valves have an increased flow resistance, which is desired for certain applications. However, if a spring acts on the first valve part and pushes the valve part away from the valve seat, then the flow valve has a reduced flow resistance until the differential pressure from the pressures in front of and behind the valve part reaches a specified value. Only then is the valve part moved towards the valve seat and against the force of the spring, which increases the flow resistance. This is usually the case when the flow valve is open to the atmosphere.

Preferably, an overpressure can be applied to the first flow channel, whereby the first valve part assumes its open position. In this way, the space in front of the flow valve in the direction of flow can be quickly ventilated and the clamped workpiece can be released. In addition, the first flow channel can be cleaned by this backflow, which is particularly advantageous in metal-cutting machines or woodworking machines.

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In a preferred flow valve, one or more proximity sensors or pressure switches are provided that determine the position of the second valve part. The proximity sensors or pressure switches are connected to a display, a control for the vacuum or the like. The position of the piston can be queried via these proximity sensors or pressure switches and the signal generated can be used for a display or to specifically control another component. In this way, it can be determined whether a workpiece is being sucked in via the flow valve or not. The proximity or pressure switches can also be used for safety purposes.

The invention also relates to a preferred use of the flow valve according to the invention for vacuum handling devices with one or more suction grippers. In addition, the flow valve can be used on machine tables for woodworking machines that have several support beams on which at least one workpiece support is movably arranged, with each support beam being equipped with several flow valves. The workpiece can rest on the workpiece supports, i.e. it is located above the flow valves, or it can hang on workpiece systems so that the flow valves are above the workpiece.

Further advantages, features and details of the invention emerge from the following description, in which particularly preferred embodiments are described in detail with reference to the drawing. The features can be used individually or in any combination. In the drawing:

Figure 1 shows a longitudinal section through a first embodiment of a flow valve;

Figure 2 shows a longitudinal section through a second embodiment of a flow valve;

Figure 3 shows a longitudinal section through a third embodiment of a flow valve;

Figure 4 is a plan view of the flow valve;

Figure 5 shows the use of the flow valve in a woodworking machine;

Figure 6 is a side view of the device according to Figure 5 in the direction of arrow VI;

Figure 7 is a plan view of the device of Figures 6 according to arrow VII;

Figure 8 is an enlarged representation of a bar according to Fig. 7; and

Figure 9 shows a flow valve screwed into a housing; and

Figure 10 is a view similar to Figure 5, but with a conventional flow valve.

In the flow valve shown in longitudinal section in Fig. 1 and designated overall by 1, flow channels 3 and 4 are provided in a valve housing 2. A first valve part 5, in this case a ball 6, is mounted in the first flow channel 3 and sits on a valve seat 7. The ball 6 divides the flow channel 3 into a front part 8, which is connected to a vacuum blower (not shown), and a rear part 9, which is connected via an external suction gripper (not shown) to the space between the flow valve 1 and an object to be gripped (not shown), from which air is to be sucked out. A flow path 10 or bypass which bypasses the valve seat 7 also opens into this rear part 9 and which, when the valve is closed, i.e. when the ball 6 is resting tightly on the valve seat 7, still enables air to be sucked out of the rear part 9.

In the flow path of the second flow channel 4 there is a second valve part 11, which in the embodiment shown in Fig. 1 is designed as a piston 12. This piston 12 can be moved in a bore 13 in the direction of the double arrow 14. The bore 13 opens into the rear part 9 of the flow channel 3 and is tightly closed at the opposite end by a suitable closure 15.

If, in a flow valve 1 designed in this way, a negative pressure is applied to the two flow outlets 16 and 17 of the two flow channels 3 and 4, and the opposite side 18 of the flow valve 1 is in contact with an object, e.g. via a suction gripper, then the pressure in the rear part 9 of the flow channel 3 is reduced. This pressure is also applied to the effective piston surface 19 of the piston 12 facing the flow channel 3, which moves from the rest position shown in Fig. 1 into a working position in which it releases the flow channel 4. In this position of the piston 12, in addition to the flow channel 3, air can also be sucked out via the flow channel 4 and the object to be lifted can be sucked in, i.e. clamped.

If this object is to be released, an overpressure is briefly applied to the flow outlet 16, whereby the pressure between the flow valve 1 and the

The space in which the object is located is ventilated. In this case, not only is any dirt that may have been sucked in and located in the rear part 9 blown out, but the piston 12 is also moved back from its working position to the rest position shown in Fig. 1, in which it closes the flow channel 4 again.

If this flow valve 1 is not in contact with an object, the two flow inlets 20 and 21 are open and connected to the atmosphere. If a negative pressure is now applied to the two flow outlets 16 and 17, then the valve formed by the ball 6 and the valve seat 7 closes and air is only sucked in via the flow path 10 from the rear part 9 of the flow channel 3. However, no negative pressure builds up there because this rear part 9 is connected to the atmosphere. The piston 12 remains in its rest position. Air is only sucked out via the flow path 10. However, its flow resistance is significantly greater than the flow resistance of the open valve. This leakage current is therefore relatively low.

In Fig. 2, a second embodiment of the flow valve 1 is shown, in which the piston 12 is divided into two sections 22 and 23. The section 22 has a larger pressure gauge than the section 23 and is guided in the bore 13. In order to

There is a sleeve-shaped insert 24 which tightly surrounds this section 23. This insert 24 is also fitted into the bore 13 and at the same time forms the closure of the bore 13. The insert 24 also has two overflow openings 25 which are aligned with the flow channel 4.

If, as described above, a negative pressure is applied to the piston surface 19 of the piston 12, it is moved to the right in the direction of the flow channel 3, and the left piston section 23 is pulled out of the insert 24, which exposes the two overflow openings 25. The flow channel 4 is now open. The piston 12 is moved so far that the left end of the section 23 is just in the insert 24. Since the piston surface 19 is larger than the opposite piston surface 26, a force acts on the piston 12 that is directed to the right when the negative pressure is the same. In this way, the switching function of the piston 12 can be adjusted to certain pressure differences.

In Fig. 2 it can also be seen that a spring 27 is arranged in the travel path of the piston 12, which exerts a force on the piston 12 that is directed to the left. A spring 27 of this kind, which is shown here only as an example and which can also be arranged on the opposite side of the piston 12,

The switching function of the piston 12 can be adapted to specific purposes. The spring can be used not only in the piston 12 shown in Fig. 2 but also in the piston 12 shown in Fig. 1 and in other embodiments.

Fig. 3 shows a third embodiment of the flow valve 1, in which the closing function for the flow channel 4 is taken over by a membrane 28. In this embodiment, a membrane insert 29 is located in the bore 13, which is provided with a transverse bore 30, a longitudinal bore 31, an annular recess 32 and a transverse bore 33 opening into this recess 32. The two transverse bores 30 and 33 open into the flow channel 4. The membrane 28 is essentially frustoconical and is clamped between the base of the bore 13 and the right-hand end face of the membrane insert 29. The membrane 28 lies sealingly on both the annular recess 32 and the coaxial longitudinal bore 31 and interrupts their connection. The contact of the membrane 28 with both the recess 32 and the longitudinal bore 31 is supported by the force of a spring 34, which pushes the membrane 28 into the rest position. The surface of the membrane 28 facing the flow channel 3 is connected to the flow channel 3 via a connecting channel 35, so that the pressure prevailing in the rear part 9 is applied to this surface. As soon as this

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If the pressure drops to such an extent that the force on the membrane 28 becomes greater than the force of the spring 34, the membrane lifts off the longitudinal bore 31 and the annular recess 32 and connects them to one another, thereby opening the flow channel 4.

Fig. 4 shows a top view of the flow valve 1 and the two flow channels 3 and 4 with their flow inlets 20 and 21. It is clearly visible that the flow valve 1 according to the invention, which is shown exaggeratedly large in the drawing, can be used as a replacement for the conventional flow valves which are screwed onto suction grippers or the like, for example.

Fig. 5 shows an application example of the flow valve 1 according to the invention, whereby for the sake of simplicity the flow valve 1 described in Fig. 1 is shown. Fig. 5 shows a section through a beam of a clamping table 37 (Fig. 6) of a woodworking machine. A large number of such flow valves 1 are arranged in this beam 36, as can be seen from Figs. 6 to 8. On these beams 36, of which three are provided for each clamping table 37, there are two workpiece supports 38, whereby the workpiece supports 38 can be moved on the beam 36 into the desired position. On the

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The workpiece 39 to be clamped, e.g. a chipboard, rests on workpiece supports 38.

Between the beam 36 and the workpiece support 38 as well as between the workpiece support 38 and the workpiece 39 there are seals 40 to 43 which define corresponding spaces 44 to 46 between them.

If a negative pressure is applied to the two flow outlets 16 and 17 of the two flow channels 3 and 4, the pressure in the rear part 9 of the flow channel 3 and in the chamber 44 drops. The negative pressure in the rear part 9 and in the chamber 44 sucks in and clamps the workpiece support 38. Since the flow channel 4 is closed by the piston 12, atmospheric pressure prevails in the chamber 45 and in the chamber 46. As soon as the pressure in the rear part 9 has reached a certain value, the piston 12 is moved from the rest position shown in Fig. 5 into a working position in which it releases the flow channel 4. The chambers 45 and 46 are now vented through the open flow channel 4 and both the workpiece support 38 and the workpiece 39 are sucked in and clamped.

The workpiece 39 is released by ventilating the chambers 45 and 46 via the flow channel 4. As long as there is a negative pressure on the flow channel 3, the piston 12 remains in its working position and the

Workpiece support 38 is clamped. The workpiece 3 can therefore be removed without the workpiece support 38 slipping.

From Figs. 6 to 8 it is clear that workpiece supports are only provided for individual flow valves 1 and that a large number of flow valves 1' are not covered by workpiece supports 38. However, since all flow valves 1 and 1' are connected to a common vacuum supply, it must be ensured that the flow valves 1' do not leak too much air. This is achieved by closing the flow channel 3 of these flow valves 1' by the ball 6, which rests on the valve seat 7. Only air flows in via the flow path 10. The flow channel 4 is closed by the piston 12.

From Fig. 8 it can be seen that for smaller workpieces 39 the workpiece supports 38 must be moved accordingly so that this small workpiece 39 can be clamped. It is only necessary to ensure that when moving the workpiece support 38 in the direction of arrow 47 it is again aligned with a flow valve 1 underneath.

Figure 9 shows the flow valve 1 according to the invention as a housing insert. The flow valve 1 has an external thread 52 on its outer circumferential surface, via which it can be

a housing 53 can be screwed in. The flow valve 1 is covered with a filter or sieve 54 to prevent dirt from entering. A proximity sensor 55 can also be seen, which is arranged in the longitudinal axis of the piston 12 and the valve housing 2 passes through the housing 53. The position of the piston 12 can be determined using this proximity sensor 55.

Figure 10 shows the use of a flow valve 48 according to the prior art. This flow valve 48 has only a single flow channel 49, which is intended to generate a negative pressure in the spaces 45 and 46. If a workpiece 39 is lying on the workpiece support 38, then the spaces 45 and 46 are vented accordingly and the workpiece support 38 and the workpiece 39 are clamped. If there is either no workpiece 39 on the workpiece support 38 or no workpiece support 38 above the flow valve 48, then the ball 50 closes the flow channel 49 and only air is sucked in via the bypass 51.

It has been found to be disadvantageous that when a clamped workpiece 39 is released, i.e. when the flow channel 49 is ventilated, not only the workpiece 39 is released but also the workpiece support 38. There is therefore a risk that this workpiece support either when the workpiece 39 is lifted off or when a new workpiece is placed on top

is moved. Then the workpiece support 3 8 is no longer aligned with the flow valve 49, which can lead to malfunctions.

Claims (18)

Protection claims 1. Vacuum clamping device with a flow valve for machine tables (37) of woodworking machines with several support beams (36) on which at least one workpiece support (38) is movably arranged, wherein each support beam (36) is equipped with several flow valves (1) and each flow valve (1) has a valve housing (2) in which a flow channel (3) is provided, wherein a movable valve part (5) is arranged in the flow channel (3) which, when a predetermined pressure difference is present, rests against a valve seat (7) and closes the flow channel (3), wherein a flow path (10) is provided which bypasses the sealing point between the movable valve part (5) and the valve seat (7), the flow resistance of which is significantly greater than. the flow resistance of the open valve, characterized in that the flow valve (1) has a second flow channel (4)/ that a second movable valve part (11) is arranged in the second flow channel (4) and that the second movable valve part (11) opens the second flow channel (4) depending on the flow direction in front of the valve seat (7) of the first opens or closes the pressure prevailing in the flow channel (3). 2. Vacuum clamping device according to claim 1, characterized in that the pressure prevailing in the second flow channel (4) and the pressure prevailing in the first flow channel (3) are applied to the second valve part (11). 3. Vacuum clamping device according to claim 1 or 2, characterized in that it has one or two flow inlets (20 and 21) and one or two flow outlets (16 and 17). 4. Vacuum clamping device according to one of the preceding claims, characterized in that the second valve part (11) closes the second flow channel (4) in its rest position. 5. Vacuum clamping device according to one of the preceding claims, characterized in that the second valve part (11) is designed as a displaceable piston (12). 6. Vacuum clamping device according to claim 5, characterized in that the piston (12) is designed as a stepped piston with different sized effective surfaces or piston surfaces (19 and 26). 7. Vacuum clamping device according to one of claims 1 to 4, characterized in that the second valve part (11) is designed as a membrane (28). 8. Vacuum clamping device according to one of the preceding claims, characterized in that on the second
Valve part (11) acts on the force of a spring (27 or 34) at least in one adjustment direction. 9. Vacuum clamping device according to one of the preceding claims, characterized in that the second
Valve part (11) replaceable in valve housing (2)
is stored. 10. Vacuum clamping device according to one of the preceding claims, characterized in that the opening or closing pressure for the second valve part (11)
is adjustable. 11. Vacuum clamping device according to one of the preceding claims, characterized in that the first
Valve part (5) by the force of a spring in
opening direction is loaded. 12. Vacuum clamping device according to one of the preceding claims, characterized in that on the first An overpressure can be applied to the flow channel (3) and the first valve part (5) assumes its open position. 13. Vacuum clamping device according to one of the preceding claims, characterized in that one or more proximity sensors or switches are provided which determine the position of the second valve part (11). 14. Vacuum clamping device according to claim 13, characterized in that the at least one proximity sensor or switch is connected to a display, a control for the vacuum or the like. 15. Vacuum clamping device according to one of the preceding claims, characterized in that it is part of a vacuum clamping device. 16. Vacuum clamping device according to one of the preceding claims, characterized in that it is arranged in a beam (36) of a clamping table (37) of a woodworking machine. 17. Vacuum clamping device according to one of the preceding claims, characterized in that the flow channels (3 and 4 or 16 and 17) can each be separately subjected to negative pressure. 26 18. Vacuum clamping device according to one of the preceding claims, characterized in that several flow valves (1) are connected to a common vacuum supply.