EP1085205A2 - Hydraulic drive - Google Patents

Abstract

The device has at least two pressure chambers (7) arranged between a stator (1) and a rotor (2), which are connected to at least partly separated hydraulic channels (11,19,22) at common hydraulic connections (20,23). The pressure chambers can be expanded, loaded and compresses alternately, so that the rotor moves with respect to the stator. A control device controls the hydraulic fluid flow. A check device (33,39) is provided in a section of hydraulic channel of at least one pressure chamber that is not part of the other pressure chamber. The flow of hydraulic fluid from the pressure chamber is prevented using the check device.

Description

The present invention relates to a hydraulic drive device, in particular rotating device for excavator grabs and the like, with a fixed component and a moving component, in particular one Stator and a rotor, at least two between the fixed Component and the moving component arranged over at least sectionally separate hydraulic lines to common Hydraulic connections connectable pressure chambers, which over the Hydraulic connections in such a manner alternately and one after the other can be pressurized with hydraulic fluid and therefore expandable as well as relieved and compressible that the moving Component moved relative to the fixed component, and a control device to control the supply and discharge of the hydraulic fluid in this Way between the pressure chambers and the common hydraulic connections.

Such drive devices are, for example, as an axial or radial piston motor known. But also vane and gear motors fall under this.

When using such drive devices as a rotating device for excavator grabs and the like, the problem arises that the gripper remains rotatable when the drive device is deactivated. Such one In many cases, twisting when the drive device is deactivated undesirable. Braking devices are therefore provided to a Prevent twisting of the gripper when the turning device is deactivated.

It is known, for example, between the stator and rotor of the rotating device to arrange a multi-disc brake, in which the multi-disc design Brake disc pairs can be pressed against each other to prevent twisting to prevent rotor from stator. Such braking devices mean of course an additional weight, and require additional Installation space. In the case of brakes acting via friction, there is also the problem that this is due to pollution and wear their function are impaired.

The invention has for its object a drive device the kind mentioned at the beginning so that these problems do not occur. In particular, the drive device with a braking device be equipped that is as light as possible and takes up little space. In addition, the braking device should be as reliable as possible his.

This object is achieved in that in a section of the hydraulic line at least one pressure chamber, which they do not share with the others Pressure chambers has in common, provided a shut-off device through which hydraulic fluid flows out of the pressure chamber is at least largely prevented.

By locking the hydraulic line, the hydraulic fluid remains in the Pressure chamber locked up. Because hydraulic fluid is practically incompressible is, further rotation of the drive device is prevented in Ideally completely blocked. A shut-off device is preferred provided on at least two pressure chambers, the diametrically opposite Phases are pressurized. This ensures that the braking effect regardless of the position of the moving component occurs immediately. It is also possible to have all pressure chambers with a shut-off device to provide to further improve the braking effect.

The braking device according to the invention is basically all types can be used by drive devices of the type mentioned, such as Axial and radial piston drives, vane-cell drives and gear drives. The control device can also in various ways be formed, for example as a plan distributor or radial distributor. But also an electrical or electronic control device in connection with a path or angle measuring device is possible. Essential is that the shut-off devices in the separate sections the hydraulic lines of the pressure chambers are arranged, thus an exchange of hydraulic fluid when the shut-off device is closed between the individual pressure chambers is prevented. The The invention is also in both endlessly rotatable drive devices as well as with only rotatable drive devices can be used, as well as fundamentally also with translatory drive devices.

According to one embodiment of the invention, the shut-off device is automatic depending on the operating state of the drive device controllable. This ensures that the shut-off device when actuated the drive device opens automatically and when the drive device is stopped locks.

According to a further embodiment of the invention, the shut-off device is directly via the drive pressure of the hydraulic fluid unlockable. This enables a control to be implemented in a structurally uncomplicated manner the shut-off device depending on the operating state of the Drive device take place.

According to a further embodiment of the invention, the pressure chambers each designed as a piston pressure chamber of a piston-cylinder arrangement, the one with the two elements, moving component and fixed Component that is firmly connected and whose pistons are on a rolling body is supported on the other element. With such an arrangement it is for example a radial piston drive or Axial piston drive, which can be used as a turning device for excavator grabs and the like have been found to be particularly advantageous.

According to a further embodiment of the invention as a rotating device The rotor and stator are non-rotatable with the other element connected, on which the rolling bodies of the pistons run. Due to the alternating The pistons are pressurized by the pressure chambers cyclically loaded in such an arrangement that piston and Cam track can be continuously rotated against each other in one direction. The cam track can be arranged on the rotor or on the stator his. Accordingly, the pistons with the other element, so stator or rotor, rotatably connected. Such an arrangement has the advantage that the rotor has a fixed axis of rotation.

According to a further embodiment of the invention, the pistons are included Sealing rings, especially piston seals, provided. This will prevents hydraulic fluid through the annular gap between pistons and cylinders can escape from the piston pressure chamber, so that a complete blocking of the drive device is made possible.

According to a further embodiment of the invention as a rotating device The rotor and stator are designed as radial distributors, with a distributor cylinder having a circular cross section and a corresponding circular cylindrical distributor receptacle, in which the distributor cylinder is rotatably guided, the distributor cylinder with one of the two elements, stator and rotor, rotatably connected and the Recording is arranged in the other element, and being the one from the other separate sections of the hydraulic lines of the pressure chambers open into the distributor receptacle and depending on the relative Rotary position of distributor cylinder and distributor holder via in The circumferential surface of the distributor cylinder alternatingly existing recesses and successively with one provided in the distributor receptacle first ring groove, which is connected to a first hydraulic connection, and a second annular groove, also seen in the receiving device, which is connected to a second hydraulic connection are. The two hydraulic connections are used for supply and discharge from hydraulic fluid to the drive device, whereby by changing Use of the connections for the supply and discharge Direction of rotation of the device can be selected.

The use of such a radial distributor has proven itself in practice. Distributor cylinder and distributor receptacle are used in such Device rotated against each other automatically with the rotation of the rotor and thereby control the supply and discharge of hydraulic fluid between the individual pressure chambers and the hydraulic connections via the individual hydraulic lines opening into the distributor receptacle. The control is done in a cost-effective and safe manner.

According to a further embodiment of the invention, the radial distributor is in the recording between a first position in which the section the hydraulic line of at least one pressure chamber, which it does not have the other pressure chambers together, is closed, and one second position, in which it is open, axially displaceable. Through the Axial displacement of the radial distributor can actuate the shut-off devices for braking the drive device in simple Way to be realized.

In particular, according to a further embodiment of the invention Sections of the hydraulic lines in the first position of the radial distributor closed by the outer surface of the distributor cylinder, while they in the second position each over the recesses in the The lateral surface is connected to the first or the second annular groove. The In this embodiment, the shut-off takes place via the sliding fit of the Distribution cylinder in the holder. So at least one braking effect, albeit due to the leakage of hydraulic fluid between Distribution cylinder and holder not completely blocked, achieved become.

According to a further embodiment of the invention is in one section the hydraulic line of at least one pressure chamber, which it does not have has a shut-off valve in common with the other pressure chambers, which counter to the force of a return spring via a plunger is adjustable in an open position, which plunger in one in the Recording the radial distributor opening recess is guided and is supported on the outer surface of the distributor cylinder, in which An annular groove is provided in the outer surface, in which the tappet in the first axial position of the distributor cylinder engages with its free end, so that the shut-off valve is closed while the plunger is in the second axial position of the distributor cylinder through its outer surface is held in the open position. Through such shut-off valves the hydraulic lines can be completely blocked. In particular in connection with the piston sealing rings, a complete Blocking of the rotating device can be achieved. Hydraulic fluid can neither between distributor cylinder and distributor holder nor between Pistons and cylinders from the pressure chambers of the locked pistons emerge.

According to a further embodiment of the invention, the distributor cylinder an axial pressure control surface to control its axial displacement on. This makes the axial displacement of the distributor cylinder easier Way.

In particular, the pressure contact surface of the distributor cylinder with drive pressure oil actable. This enables the distributor cylinder to operate automatically axially shifted when the drive device is actuated and the Braking device can be released. An external control is also possible.

Instead of an axial displacement of the distributor cylinder can also an axially displaceable sleeve can be provided which comprises the distributor and the hydraulic lines opening into the receptacle in an axial Locks position and releases in the other axial position.

A particular advantage of the design with an axially displaceable distributor cylinder is also that the drive device with and can be constructed identically without a braking device. In the variant without a braking device, only the distributor cylinder must be corresponding axially longer, or a suitable spacer must be used be provided for axial displacement of the distributor cylinder to prevent.

According to a further embodiment of the invention is in one section the hydraulic line of at least one pressure chamber, which it does not have the other pressure chambers have in common, an unlockable check valve arranged. In this embodiment, the flow of Hydraulic fluid through the hydraulic lines so not over the Distribution cylinder controlled. Instead, are in the hydraulic lines Check valves are provided, through which the pressure chambers due of the hydraulic pressure there are closed when the Check valves cannot be unlocked. This is also a complete one Blocking of the drive device possible.

The check valves are unlocked according to a further embodiment the invention preferably over the drive pressure oil. This will again achieved that the braking device when actuating the drive device is solved automatically. An external control is also possible.

According to a further embodiment of the invention, at least one Pressure chamber arranged a pressure relief valve. So that becomes a Damage to the drive device prevented if too large Torque on the moving component when the drive device is blocked works. A pressure relief valve is preferred in all pressure chambers intended. This can damage the drive device can be prevented particularly effectively.

Fig. 1

einen Querschnitt durch eine erste Variante der erfindungsgemäßen Antriebsvorrichtung,

Fig. 2

einen Querschnitt durch eine zweite Variante der erfindungsgemäßen Antriebsvorrichtung und

Fig. 3

einen Querschnitt durch eine dritte Variante der erfindungsgemäßen Antriebsvorrichtung.

Embodiments of the invention are shown in the drawing and are described below. They show, each in a schematic representation,

Fig. 1

3 shows a cross section through a first variant of the drive device according to the invention,

Fig. 2

a cross section through a second variant of the drive device according to the invention and

Fig. 3

a cross section through a third variant of the drive device according to the invention.

The hydraulic drive device shown in Fig. 1 comprises a Stator 1, which for example with an excavator boom, not shown is connectable, and a rotatably mounted on the stator about an axis I. Rotor 2, on which, for example, an excavator grab, also not shown is attachable. Stator 1 and rotor 2 can also be reversed be mounted so that the stator 1 to the rotor and the rotor 2 to Stator will. The drive acting between stator 1 and rotor 2 comprises a plurality of piston-cylinder arrangements arranged radially to the axis of rotation I in the stator 1 3. The cylinders of the piston-cylinder assemblies 3 are each by a circular cylindrical in cross section Recess 4 formed in the stator 1, in which a piston 5 in the radial direction is guided. Between the radially inner The bottom 6 of the recess 4 and the piston 5 are each a piston pressure chamber 7 trained. In this piston pressure chamber 7 there is one Compression spring 8 is arranged, which is supported on the base 6 of the recess 4 and pushes the piston 5 radially outwards.

On the side of the piston 5 facing away from the piston pressure chamber 7 a roller-shaped rolling body 9 is provided, which on the piston 5 is rotatably mounted on the piston 5 about an axis II parallel to the axis I. By the compression spring 8 acting on the piston 5, the rolling body 9 pushed against a curved path 10, which is opposite the piston 5 on the rotor 2 is provided. The distance of the curved path 10 from the Rotation axis I changes cyclically around the rotation axis I between one maximum distance at which the piston 5 is extended, and a minimum distance at which the piston 5 is retracted.

The piston pressure chamber 7 of the piston-cylinder arrangements 3 is in each case via a hydraulic channel 11 with a central provided in the stator 1 Recess 12 in connection, the free cross section essentially the shape of a circular cylinder extending in the direction of the axis I. has and which serves as a distributor receptacle. In this shot 12 is a distributor cylinder 13 with a substantially circular shape Cross section used by the receptacle 12 about the axis of rotation I pivoted and between a first axial position and a second axial position is guided. The first axial position of the Distribution cylinder 13 is through the bottom 14 of the receptacle 12 determines the second axial position by the rotor 2, which with the stator 1 is rotatably connected about the axis I. Over one into an end Recess 15 of the distributor cylinder 13 engaging driver pin 16 the distributor cylinder 13 is rotatably connected to the rotor 2.

In the inner peripheral surface 17 of the receptacle 12 there is a first annular groove 18 introduced via a hydraulic channel 19 with a first hydraulic connection 20 is connected. Furthermore, is in the inner peripheral surface 17 of the receptacle 12, a second annular groove 21 is introduced, which has a Hydraulic channel 22 connected to a second hydraulic connection 23 is. To the hydraulic connections 20 and 23, for example, from one Excavator boom coming hydraulic lines connected are used to supply and discharge hydraulic fluid. Via recesses 24 in the cylinder jacket surface 25 of the distributor cylinder 13 are the hydraulic channels leading to the piston pressure chambers 7 11 depending on the rotational position of the distributor cylinder 13 alternately one after the other with the annular groove 18 and the other Ring groove 21 connected. In this way, the pressure spaces 7 are alternated pressurized with hydraulic oil and relieved.

When loading a pressure chamber 7 by supplying hydraulic fluid Via the first hydraulic connection 20, channel 19, annular groove 18, a recess 24 and the associated hydraulic channel 11, the piston 5 the associated piston-cylinder arrangement 3 pushed radially outwards. As a result, the rolling body 9 of this piston-cylinder arrangement 3 on the cam track 10 down the slope, ie radially outwards moves so that the piston 5 can extend radially. That is, since the Cam track 10 is attached to the rotor 2, the cam track moves 10 with the rotor 2 corresponding to the axis of rotation I. After reaching a Tales of the cam track 10, the hydraulic channel 11 over the next Recess 24 connected to the other annular groove 21, which over the Channel 22 is connected to the second hydraulic connection 23. Now the piston 5 can move radially into the recess 4 and the rolling body 9 on the curved path 10 up the slope, that is to say radially inwards, unroll. As a result, the rotor 2 continues to rotate in the same direction the axis of rotation I. Correspondingly, the pressure spaces 7 of the others Piston-cylinder arrangements 3 alternately acted upon with hydraulic fluid and relieved, so that a continuous movement arises. By swapping the supply and discharge of the hydraulic fluid over the connections 20 and 23 can reverse the direction of rotation of the device become.

The distributor cylinder 13 has a pressure contact surface directed transversely to the axis of rotation I. 26 on that between a distributor cylinder 13 and Distributor receptacle 12 formed annular space 27, which is via a hydraulic channel 28 can be connected to the hydraulic fluid supply, with Drive pressure can be applied. A changeover valve 29 ensures that the annular space 27 in both directions of rotation of the device hydraulic fluid is applied.

When the annular space 27 is acted upon by hydraulic fluid Distributor cylinder 13 against the force of a return spring 30 axially in Moved towards the rotor 2. When the pressure contact surface is relieved 26 the distributor cylinder 13 moves away under the force of the return spring 30 from the rotor 2 until the distributor cylinder 13 at the base 14 of the receptacle 12 strikes. This position is shown in Fig. 1. This leaves between Distributor cylinder 13 and receptacle 12, a small annular space 27, over which hydraulic cylinder is again applied to the distributor cylinder 13 can be.

While in the second position of the distributor cylinder, not shown here 13, the recesses 24 each have an annular space 18 or 21 connect the hydraulic channels 11 of the piston-cylinder arrangements 3, is in the first axial position of the distributor cylinder shown in Fig. 1 13 no such connection was given. Rather, the recesses 24 only with the ring channel 18 or only with a hydraulic channel 11 connected. The annular groove 21 and part of the hydraulic channels 11 is, however, closed by the outer surface 25 of the distributor cylinder 13. As a result, no hydraulic fluid can escape from the piston pressure chambers 7 flow away. There is only some leakage between the distributor cylinder 13 and recording 12. The rotor is opposite to that Stator 1 braked against twisting, since the pistons 5 do not or only very slowly according to the amount of leakage in the recesses 4 can drive in.

To avoid damaging the drive device if at Blocking the drive device an excessive torque on the Rotor 2 acts, is in the piston 5 each with the piston pressure chamber 7 connected and in the low pressure chamber 31 between the rotor 2 and the stator 1 opening pressure relief valve 32 is provided.

The variant shown in FIG. 2 is largely correct with the variant of FIG. 1 match. In contrast to this first variant, however, is here in the hydraulic channels 11 between the piston pressure chamber 7 and the receptacle 12 each a shut-off valve 33 is arranged, which via a tappet 34th against the force of a return spring 35 in the open position is. The plunger 34 is in a recess 36 between the hydraulic channel 11 and 12 guided and supported with his free end 37 on the cylinder jacket surface 25 of the distributor cylinder 13 from. In addition, in the cylinder jacket surface 25 of the distributor cylinder 13 introduced an annular groove 38, in which the plunger 34 with its free End 37 can retract when the distributor cylinder 13 in its from Rotor 2 is in the distant position. This situation is in the left Half of Fig. 2 shown. In this retracted into the annular groove 38 Position of the plunger 34, the shut-off valve 33 is closed while it with axial displacement of the distributor cylinder 13 in the direction of Rotor 2 by moving the plunger 34 over the lateral surface 25 of the Distributor cylinder 13 is opened. This situation is in the right Half of Fig. 2 shown.

As before, the hydraulic channels 11 are between the piston pressure chambers 7 and the receptacle 12 in the first axial position of the distributor cylinder 13, in which this is not acted upon by the drive pressure is closed while in the second axial position of the Distributor cylinder 13, in which this is acted upon by the drive pressure is, depending on the rotational position of the distributor cylinder 13 either with the first annular groove 18 or with the second annular groove 21 via the recesses 24 connected in the cylinder jacket surface 25 of the distributor cylinder 13 are. In contrast to the previous variant, the closure is of the cylinder pressure chambers 7 due to the use of the shut-off valves 33 but absolutely tight, so that none from the piston pressure chambers 7 Leakage fluid can leak. The rotating device is thereby complete blocked. In this variant, too, the pistons 5 have the pressure relief valves opening the low pressure chamber 31 between the stator 1 and the rotor 2 32 on damage to the drive device to avoid excessive force on the rotor 2.

In the variant shown in Fig. 3, the drive agrees with the two previous variants basically match. The distributor cylinder 13 is but not axially displaceable here. Instead it is in the Hydraulic lines 11 between the piston pressure chambers 7 and the receptacle 12 each have an unlockable check valve 39, through which the piston pressure spaces 7 can be completely shut off. The The check valves 39 are unlocked via the drive pressure, with which the check valves 39 can be acted upon via hydraulic channels 40 are, which in turn, are connected to the shuttle valve 29, so that unlocking the check valves 39 in both directions the drive device takes place. When the drive device is actuated So all check valves 39 are unlocked, so that the piston pressure chambers 7 of the piston-cylinder arrangements 3 via the hydraulic channels 11 in each case either with the first annular space 18 or with the second annular space 21 are connected, depending on the rotational position of the distributor cylinder 13, so that the piston pressure spaces 7 according to the cycle either with hydraulic fluid be charged or relieved.

While the first variant of the drive device according to the invention acts as a brake, the second and third variants lead to a blockage the drive device. Depending on your needs, one or the other Variant can be selected. In any case, the braking or blocking device structurally inexpensive, taking up little space and light. In addition, it is reliable. In particular, none occurs Functional impairment due to contamination and wear.

Reference list

1

stator

2nd

rotor

3rd

Piston-cylinder arrangement

4th

Recess

5

piston

6

Reason of 4

7

Piston pressure chamber

8th

Return spring

9

Roll body

10th

Cam track

11

Hydraulic channel

12th

admission

13

Distributor cylinder

14

Reason of 12

15

Recess in 13

16

Driver pin

17th

Inner circumferential surface of 12

18th

first ring groove

19th

Hydraulic channel

20th

first hydraulic connection

21

second ring groove

22

Hydraulic channel

23

second hydraulic connection

24th

Recess in 25th

25th

Outer surface of 13

26

Pressure pad

27

Annulus

28

Hydraulic channel

29

Shuttle valve

30th

Return spring

31

Low pressure room

32

Pressure relief valve

33

Shut-off valve

34

Pestle

35

Return spring

36

Recess

37

free end of 34

38

Ring groove

39

unlockable check valve

40

Hydraulic channel

I.

Axis of rotation of 2

II

Axis of rotation of 9

Claims (12)

Hydraulic drive device, in particular a rotating device for excavator grabs and the like, with a stationary component (1) and a moving component (2), in particular a stator (1) and a rotor (2), at least two between the stationary component (1) and the moving component ( 2) arranged pressure chambers (7) which can be connected to at least sections of hydraulic lines (11, 19, 22) to common hydraulic connections (20, 23) and which can be pressurized alternately and in succession with hydraulic fluid via the hydraulic connections (20, 23) and are expandable, relievable and compressible in that the moving component (2) moves relative to the fixed component (1), and a control device for controlling the supply and discharge of the hydraulic fluid in this way between the pressure chambers (7) and the common one Hydraulic connections (20, 23),
characterized in that in a section (11) of the hydraulic line of at least one pressure chamber (7), which it does not have in common with the other pressure chamber (7), a shut-off device (33, 39) is provided, through which hydraulic fluid flows out of the Pressure chamber (7) is at least largely prevented. Drive device according to claim 1,
characterized in that the shut-off device (33, 39) can be controlled automatically as a function of the operating state of the drive device, the shut-off device (33, 39) in particular being unlockable directly via the drive pressure of the hydraulic fluid. Drive device according to one of the preceding claims,
characterized in that the pressure chambers (7) are each designed as a piston pressure chamber of a piston-cylinder arrangement (3). are, which is firmly connected to one of the two elements, fixed component (1) and moving component (2) and whose piston (5) is supported on the other element via a rolling body (9). Drive device according to claim 3,
characterized in that it is designed as a rotating device with a stator (1) and rotor (2) and that with the other element a cam track (10) is rotatably connected, on which the rolling bodies (9) of the pistons (5) run. Drive device according to claim 3 or 4,
characterized in that the pistons (5) are provided with sealing rings, in particular piston seals. Drive device according to one of the preceding claims,
characterized in that it is designed as a rotating device with a stator (1) and rotor (2) and that the control device is designed as a radial distributor, with a distributor cylinder (13) with a circular cross section and a corresponding circular cylindrical receptacle (12) in which the Distribution cylinder (13) is rotatably guided, the distribution cylinder (13) with one of the two elements, stator (1) and rotor (2), rotatably connected and the receptacle (12) is provided in the other element, and wherein the separate Sections (11) of the hydraulic lines of the pressure chambers (7) open into the receptacle (12) and, depending on the relative rotational position of the distributor cylinder (13) and receptacle (12), via recesses () in the lateral surface (25) of the distributor cylinder (13). 24) alternately and in succession with a first annular groove (18) provided in the receptacle (12) and connected to a first hydraulic connection (20) i st, and a second annular groove (21) which is also provided in the receptacle (12) and is connected to a second hydraulic connection (23). Drive device according to claim 6,
characterized in that the distributor cylinder (13) in the receptacle (12) is closed between a first position in which a section (11) of the hydraulic line has at least one pressure chamber (7) which it does not have in common with the other pressure chambers (7) are, and a second position in which it is open, is axially displaceable. Drive device according to claim 7,
characterized in that the sections (11) of the hydraulic lines are closed in the first position by the lateral surface (25) of the distributor cylinder (13), while in the second position they are closed by the recesses (24) in the lateral surface (25) of the distributor cylinder ( 13) are each connected either to the first annular groove (18) or to the second annular groove (21). Drive device according to claim 7,
characterized in that in each section (11) of the hydraulic line of at least one pressure chamber (7), which it does not have in common with the other pressure chambers (7), a shut-off valve (33) is arranged which counteracts the force of a return spring (35) A plunger (34) can be adjusted into an open position, which plunger (34) is guided in a recess (36) opening into the receptacle (12) of the radial distributor and is supported on the lateral surface (25) of the distributor cylinder (13), whereby an annular groove (38) is provided in the lateral surface (25), into which the plunger (34) can move with its free end (37) in the first axial position of the distributor cylinder (13), so that the shut-off valve (33) is closed , while the plunger (34) is held in the second axial position of the distributor cylinder (13) by its outer surface (25) in the open position. Aria drive device according to one of claims 7 to 9,
characterized in that the distributor cylinder (13) has an axial pressure setting surface (26) for controlling its axial displacement, the pressure setting surface (26) preferably being pressurized with drive pressure oil. Drive device according to one of claims 1 to 6,
characterized in that an unlockable check valve (39) is arranged in a section (11) of the hydraulic lines of at least one pressure chamber (7), which it does not have in common with the other pressure chambers (7), the check valves (39) preferably via the drive pressure oil can be unlocked. Drive device according to one of the preceding claims,
characterized in that a pressure limiting valve (31) is arranged in at least one pressure chamber (7) and opens into a low-pressure chamber (31) of the drive device.

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