JP4148785B2 - Seal device for fluid pressure equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sealing device for a sliding portion of a rod in a fluid pressure device in which gas is sealed or a fluid pressure device that is operated by introducing gas.
[0002]
[Prior art]
A gas spring is widely used as a fluid pressure device in which a pressurized gas is sealed inside the cylinder, and a pneumatic cylinder is widely used as a fluid pressure device that introduces and operates the pressurized gas inside the cylinder. Each of these devices applies the force of the pressurized gas inside the cylinder to an external load by a rod that reciprocates through the rod cover.
[0003]
Among them, the gas spring uses a large repulsive force generated by compressing the sealed gas inside the cylinder when the rod is pushed into the cylinder. That is, by keeping this repulsive force balanced with the load applied to the rod, a large load can be supported by a slight force for breaking this balance, and the load can be moved. Conventionally, gas springs have been widely used for opening / closing assistance of a door portion of a rear luggage compartment of an automobile, a cover portion of OA equipment or a lid portion of a small industrial equipment. In recent years, gas springs are attached to the spindle lifting device of a machining center, which is a machine tool, to balance the spindle load, and to raise and lower the spindle with less power and at the same time improve the spindle position accuracy and improve machining accuracy. Is also used.
[0004]
On the other hand, pneumatic cylinders, for example, are easily used for removal of defective products in product inspection lines, product sorting operations in the distribution process, and automation of production processes such as opening and closing of valves. It is also used for machine tools that require large pressure.
[0005]
As described above, in widely used gas springs and pneumatic cylinders, gas leakage from the inside of the cylinder to the outside of the cylinder, in particular, the inner peripheral surface of the through hole of the rod cover and the inner peripheral surface slide. Gas leakage from the outer peripheral surface of the rod (hereinafter referred to as “rod sliding portion”) is more likely to occur as the gas pressure inside the cylinder becomes higher, and it is not easy to prevent.
[0006]
In particular, in a gas spring used in a state in which gas is sealed, if there is even a slight gas leak from the inside of the cylinder, the gas pressure will drop during long-term use, and the required gas spring The performance (initial load) is not obtained.
[0007]
In particular, when a gas spring is used in a machine tool such as a machining center or a press machine, an excessive load is applied to the lifting device such as the spindle, which lowers the machining accuracy of the machine tool and improves the quality of the processed product. May lead to decline. Therefore, it has been required to keep the sealing performance of the portion where the rod slides for a long period of time and to prevent gas leakage from the inside of the cylinder.
[0008]
Conventionally, as a sealing method of a portion where the rod slides, for example, a structure using a U-packing 84 shown in FIG. 6 is employed in a small gas spring. For the purpose of lubricating the sliding portion between the rod 82 and the rod bush or rod cover 83, the inner surface of the rod bush or rod cover 83 on which the rod 82 slides is positioned between the U packing 84 and the dust seal 86. The structure which provides the annular groove | channel which encloses and lubricates lubricating oil is also used.
[0009]
However, the difference between the gas pressure inside the gas spring (hereinafter referred to as “gas chamber”) 85 and the pressure outside the gas spring is several MPa to 7 MPa or more, and the force due to this pressure difference is applied to the U-packing 84. It will be. Due to the pressure difference, the sliding side lip 841 of the U-packing 84 is strongly pressed against the rod 82, and the sliding side lip 841 having increased sliding resistance is easily worn by the reciprocating motion of the rod 82. As a result of wear of the sliding side lip 841, it is considered that the sealing performance of the U-packing 84 is lowered, and there is anxiety about long-term use of the gas spring. In order to lubricate the part where the rod slides, a small amount of lubricating oil is sealed inside the cylinder, but the gas spring must be installed with the part where the rod slides down. There are usage restrictions.
[0010]
In the structure in which lubricating oil is enclosed in the annular groove between the U packing 84 and the dust seal 86, the enclosed lubricating oil forms an oil film on the outer peripheral surface of the rod 82, and slides on the outer peripheral surface of the rod 82 due to the effect of the oil film. It can be expected that the frictional force with the side lip 841 is reduced. However, since the pressure of the lubricating oil sealed in the annular groove is lower than the pressure in the gas chamber, there is a possibility that gas leaks to the outside through the annular groove. Furthermore, since the lubricating oil gradually decreases due to frequent reciprocation of the rod, there is a possibility that the problem of deterioration of the sealing performance may occur as in the sealing structure shown in FIG.
[0011]
Therefore, a seal structure that can be replenished with lubricating oil has been proposed (see Patent Document 1). However, in the gas spring seal structure disclosed in Patent Document 1, the pressure in the lubricating oil storage portion is lower than the pressure in the gas chamber, and the risk of gas leaking outside through the lubricating oil storage portion is eliminated. Not.
[0012]
In addition, instead of a seal structure that appropriately replenishes the reduced lubricant, a seal structure that continuously supplies pressurized lubricant to the annular groove on the inner peripheral surface of the rod cover is also considered (see Patent Document 2). In the structure shown in this Patent Document 2, the pressure of the lubricating oil is lower than the gas pressure inside the cylinder. Therefore, similarly to the seal structure described in Patent Document 1, the gas in the gas chamber may leak through the seal portion. In this seal structure, the gas spring is always connected to the lubricating oil pressurizing mechanism and the lubricating oil filling mechanism, which requires peripheral equipment, which complicates the equipment and includes factors that increase running costs. It is out.
[0013]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-293622 (page 3-4, FIG. 1)
[0014]
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-96229 (pages 3 and 4 and FIGS. 2 and 5)
[0015]
[Problems to be solved by the invention]
The pressure of the gas chamber of the pneumatic cylinder is generally 1 MPa or less, and the pressure of the gas chamber of the gas spring is generally several MPa to around 7 MPa. However, gas sealing is not easy even when the pressure is low, and it is troublesome to replenish the gas once the gas leaks to the outside, especially in a device in which pressurized gas is sealed, such as a gas spring. It is often a difficult task.
[0016]
The present invention provides a sealing device that improves the sealing performance between the inner peripheral surface of the through hole of the rod cover and the outer peripheral surface of the rod that slides on the inner peripheral surface in the fluid pressure device and increases the durability of the seal member. The purpose is to provide.
[0017]
[Means for Solving the Problems]
In the sealing device according to the present invention, a rod is movably inserted into a through hole of a cover that closes one end of a cylinder tube, and pressurized gas is sealed or pressurized in a gas chamber formed inside the cylinder tube. A sealing device for sealing the gas in the gas chamber in the through hole for a fluid pressure device into which the gas is introduced, the annular oil chamber provided on the inner peripheral surface of the through hole, and the through A seal member that is provided on an inner peripheral surface of the hole and seals between the gas chamber and the oil chamber; an oil passage that is provided in the cover and communicates between the outside of the cover and the oil chamber; and the oil chamber A pressure regulating path formed so as to communicate with the gas chamber, and a pressure transmission device provided so as to protrude from the cover into the gas chamber so as to block the pressure regulating path. The device A transmission member that is movable or deformable according to the differential pressure on both sides of the blocked passage and is blocked, on the side communicating with the oil chamber of the oil chamber, the oil passage, and the pressure regulating passage Is filled with oil and configured to transmit the pressure of the gas in the gas chamber to the oil in the oil chamber via the pressure transmission device.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
1 is a front sectional view of a gas spring 1 provided with a sealing device 2 according to an embodiment of the present invention, FIG. 2 is a partial front sectional view showing an enlarged seal portion of FIG. 1, and FIG. FIG. 4 is a front sectional view of the pressure transmission device 3 constituting the sealing device 2, and FIG. 5 is a front sectional view of another embodiment of the pressure transmission device 3.
[0019]
As shown in FIG. 1, the gas spring 1 has a rod cover 14 at one end of a cylinder tube 11 and a head cover 16 at the other end. The rod bush 13 is attached to the rod cover 14 with the rod 12 inserted.
[0020]
Both ends of the cylinder tube 11 are closed by the rod cover 14 and the head cover 16, and a gas chamber 15 is formed inside the closed cylinder tube 11. The head cover 16 is provided with a gas injection port 17 for injecting nitrogen gas into the gas chamber 15.
[0021]
On the inner peripheral surface 133 of the through hole of the rod bush 13 into which the rod 12 is inserted, a circle that is approximately half the length of the rod bush 13 in the axial direction and is shallow in the radial direction is approximately in the center in the axial direction. An annular groove is provided. An oil chamber 21 is formed surrounded by the annular groove and the outer peripheral surface 121 of the rod 12. The depth of the annular groove shown in FIG. 1 is about 2 mm, but this can be arbitrarily set in consideration of the size of the gas spring 1 and the like.
[0022]
2 and 3, the rod bush 13 has two holes 131, 131 that penetrate the oil chamber 21 and the outer peripheral surface of the rod bush 13 at positions spaced apart from each other in the axial direction and in the circumferential direction. Are provided at intervals of 180 degrees. Although the number of holes 131 may be one instead of two, it is preferable to provide one or more holes at both ends in the axial direction of the oil chamber 21 in order to smoothly vent air when the oil is sealed in the oil chamber 21.
[0023]
As shown well in FIG. 2, the first seal member 41 and the second seal member 42 are provided on the inner peripheral surface 133 of the through hole of the rod bush 13 on both sides in the axial direction across the oil chamber 21.
[0024]
The first seal member 41 is between the gas chamber 15 and the oil chamber 21, and the second seal member 42 is between the oil chamber 21 and the outside, the outer peripheral surface 121 of the rod 12 and the inner peripheral surface 133 of the rod bush 13, respectively. It is for sealing in the sliding part. In the present embodiment, as the first seal member 41 and the second seal member 42, a combination seal in which an O-ring and a resin seal are combined is used.
[0025]
As shown in FIGS. 1 and 2, an annular gap 132 is formed between the outer peripheral surface of the rod bush 13 and the inner peripheral surface of the rod cover 14.
That is, the rod bush 13 is provided with a first outer peripheral surface 135 having a maximum diameter, a second outer peripheral surface 136 having an intermediate diameter, and a third outer peripheral surface 137 having a minimum diameter. The rod cover 14 is substantially the same as the first inner peripheral surface 145 having the same inner diameter as the first outer peripheral surface 135, the second inner peripheral surface 146 having the same inner diameter as the second outer peripheral surface 136, and the third outer peripheral surface 137. A third inner peripheral surface 147 having an inner diameter is provided. The third outer peripheral surface 137 is longer than the third inner peripheral surface 147 in the axial direction, and the second outer peripheral surface 136 is shorter than the second inner peripheral surface 146 in the axial direction. When the rod bush 13 is attached to the rod cover 14, an annular gap 132 is formed by the third outer peripheral surface 137 and the second inner peripheral surface 146. The gap 132 has a radial width corresponding to one half of the difference in outer diameter between the second outer peripheral surface 136 and the third outer peripheral surface 137, and the third outer peripheral surface 137 and the third inner peripheral surface 147 (or the second inner peripheral surface). It has a length corresponding to the difference in axial length between the peripheral surface 146 and the second outer peripheral surface 136).
[0026]
The axial position and length of the gap 132 are determined so that the hole 131 opens into the gap 132. The width of the gap 132 shown in FIG. 1 is about 3 mm, and the length in the axial direction is approximately half the axial thickness of the rod cover 14. The gap 132 is formed so as to communicate with an oil supply passage 141 provided in the rod cover 14 described later.
[0027]
However, the radial width and the axial length of the gap 132 vary depending on the size and application of the gas spring 1 and are not limited to the dimensions described above. Further, the gap 132 is not limited to a shape having an annular cross section as shown in FIG. 3 as long as the oil supply passage 141 and the hole 131 are connected to supply oil to the oil chamber 21. For example, one groove provided in the second outer peripheral surface 136 may be provided so that the hole 131 and the oil supply passage 141 communicate with each other without providing the third outer peripheral surface 137 and the third inner peripheral surface 147.
[0028]
As described above, the rod cover 14 is provided with the oil supply passage 141, one of which opens into the gap 132 and the other of which opens to the outside on the side surface of the rod cover 14. An oil supply port 144 is provided on the side surface of the rod cover 14 where the oil supply path 141 is opened. Note that a closing valve (not shown) is attached to the fuel supply port 144. The rod cover 14 is provided with an air vent path 142 for venting air when supplying oil to the oil chamber 21. A plug 143 is attached to the side surface of the rod cover 14 where the air vent path 142 opens. The oil passage 22 is formed by the hole 131, the gap 132, and the oil supply passage 141.
[0029]
Further, the rod cover 14 is provided with a pressure regulating path 23 that branches off from the oil supply path 141 and communicates with the gas chamber 15. That is, the pressure regulation path 23 communicates the gas chamber 15 and the oil chamber 21 through the oil supply path 141.
[0030]
The pressure transmission device 3 is attached to a portion of the pressure regulating path 23 that opens to the gas chamber 15. The pressure transmission device 3 transmits the pressure in the gas chamber 15 to the oil chamber 21, and the difference between the gas pressure in the gas chamber 15 and the oil pressure in the oil chamber 21 with the first seal member 41 interposed therebetween is set to an appropriate magnitude. Play a role to keep.
[0031]
In FIG. 4, the pressure transmission device 3 includes a small cylinder tube 31 and a small piston 32 that slides on the inner peripheral surface of the small cylinder tube 31 and blocks oil and gas. The small piston 32 functions to transmit the gas pressure in the gas chamber 15 to the oil in the oil chamber 21. Since the pressure receiving areas on both sides of the small piston 32 are equal, the pressure in the gas chamber 15 is transmitted to the oil chamber 21 as it is.
[0032]
The small cylinder tube 31 is provided with a male screw on the outer periphery of one opening 34, and is screwed into a female screw provided in the opening of the pressure adjusting path 23 and attached to the rod cover 14. An opening plug 37 is provided in the other opening 35 of the small cylinder tube 31. The opening plug 37 is provided with a through hole 36 in the central portion, and gas can flow without a pressure drop.
[0033]
The small piston 32 is formed so as to easily slide on the inner peripheral surface of the small cylinder tube 31 by the differential pressure between the gas pressure in the gas chamber 15 and the oil pressure in the oil chamber 21. A spring 33 is mounted between the small piston 32 and the opening plug 37. Accordingly, the small piston 32 is biased by the spring 33 and moves to the left end of FIG. 4 in its free state.
[0034]
In addition, the spring 33 in this embodiment has a small spring constant and urging force, and is provided to make the movement of the small piston 32 smooth. The small piston 32 and the spring 33 may or may not be fixed. When it is desired to keep the oil pressure in the oil chamber 21 higher than the gas pressure in the gas chamber 15, a spring 33 having a large spring constant and urging force may be used.
[0035]
The sealing device 2 is filled with oil having lubricity. The oil is sealed in the sealing device 2 as follows.
A stop valve is attached to the oil supply port 144 as described above, and an oil supply hose or the like is connected to the port of the stop valve. At that time, a hydraulic gauge is connected. The plug 143 of the air vent path 142 is loosened, the shut-off valve is opened, and oil supply is started, and the oil path 22, the oil chamber 21, and the pressure transmission device 3 are filled with oil. When oil leaks from the stopper 143, the oil supply is stopped once and the stopper 143 is closed. Thereafter, refueling is resumed, and the refueling is stopped when the pressure of the oil pressure gauge increases. The refueling after closing the plug 143 is for moving the small piston 32 of the pressure transmission device 3 to the gas chamber 15 side. After stopping the oil supply, the shutoff valve attached to the oil supply port 144 is closed and the oil supply hose is removed. Refueling is performed with care so that no air remains in the oil chamber 21 or the like as much as possible. It is effective to slowly move the entire gas spring 1 up and down and left and right so that air remaining in the oil chamber 21 and the like is guided to the air vent path 142 in the middle of refueling.
[0036]
Filling the gas chamber 15 in the gas spring 1 with the pressurized gas is performed by connecting a gas supply pipe to the gas injection port 17. For example, nitrogen gas is used as the gas. Nitrogen gas is injected, for example, from a nitrogen cylinder by reducing the pressure to a predetermined pressure via a pressure reducing valve.
[0037]
The pressure of the oil in the oil chamber 21 is about atmospheric pressure to about 0.1 MPa before the gas chamber 15 is filled with nitrogen gas. As the pressure in the gas chamber 15 increases due to the injection of the pressurized gas into the gas chamber 15, the pressure is transmitted to the oil by the small piston 32, and the oil pressure in the oil chamber 21 increases. As a result, the oil chamber 21 has substantially the same pressure as the gas chamber 15.
[0038]
As described above, the pressure transmission device 3 functions to transmit the pressure of the gas in the gas chamber 15 to the oil in the oil chamber 21 when the gas spring 1 is operated. By this function, there is almost no pressure difference between the oil in the oil chamber 21 and the gas in the gas chamber 15, and the gas in the gas chamber 15 is less likely to leak from the seal portion of the first seal member 41 to the oil chamber 21. Further, since there is almost no pressure difference between the oil in the oil chamber 21 and the gas in the gas chamber 15, the wear of the first seal member 41 that slides on the outer peripheral surface of the rod 12 is reduced.
[0039]
That is, the sealing device 2 in the present embodiment can enhance the durability of the seal portion while maintaining high sealing performance of the portion where the rod 12 slides.
In the gas spring 1 described above, the requirements for the first seal member 41 in order to maintain the sealed state are greatly relaxed compared to what is expected from the magnitude of the gas pressure in the gas chamber 15. It will be a thing. Therefore, various types of seals can be used for the first seal member 41, and for example, an O-ring can be used alone.
[0040]
When the pressure of either the gas in the gas chamber 15 or the oil in the oil chamber 21 is set higher than the other, a lip packing such as U packing, V packing, or L packing is used for the first seal member 41. Is preferred. At this time, the lip of the packing is provided so as to face the higher pressure side of the gas chamber 15 and the oil chamber 21.
[0041]
The second seal member 42 is for sealing the outside of the gas spring 1 and the oil chamber 21 at the sliding portion between the outer peripheral surface 121 of the rod 12 and the inner peripheral surface 133 of the rod bush 13. Therefore, the second seal member 42 is a type of packing that exhibits a sufficient sealing performance even when used for a sliding portion having a large pressure difference. For example, it is preferable to use a lip packing such as a U packing, a V packing and an L packing suitable for sealing a reciprocating shaft of a hydraulic device. The lip of the packing is arranged so as to face the oil chamber 21 side.
[0042]
FIG. 5 is a diagram illustrating a pressure transmission device 3B according to another embodiment.
The pressure transmission device 3B includes a container 31B and a bellows 32B inside the container 31B. The container 31B has two openings 34B and 35B, and the two openings 34B and 35B are completely blocked by the bellows 32B inside the container 31B. The pressure transmission device 3 </ b> B is connected to the pressure adjusting path 23 so that one opening 34 </ b> B communicates with the oil chamber 21 and the other opening 35 </ b> B communicates with the gas chamber 15. The bellows 32B expands and contracts inside the container 31B due to a change in the gas pressure in the gas chamber 15, and transmits the pressure in the gas chamber 15 to the oil inside the bellows 32B. The pressure of the oil inside the bellows 32 </ b> B is transmitted to the oil chamber 21 through the pressure adjusting path 23. You may connect to the pressure regulation path 23 so that the opening part 34B may be connected to the gas chamber 15, and the opening part 35B may be connected to the oil chamber 21.
[0043]
In addition to the embodiment described above, the pressure transmission device may be provided with a metal diaphragm in place of the bellows 32B in the pressure transmission device 3B. Further, instead of the pressure transmission device 3, a simple structure may be adopted in which the opening to the gas chamber 15 of the pressure adjusting path 23 is closed with a transmission member having elasticity such as a bellows, a metal diaphragm, or a non-metallic elastic film. However, when a metal diaphragm is used for the transmission member, since the tolerance for deformation is smaller than when the bellows 32B is used, management is performed to maintain the amount of oil in the oil chamber 21 in order to maintain the sealing performance. Is preferred.
[0044]
When there is no space for providing a transmission device inside a fluid pressure device such as a gas spring, the pressure transmission device 3B can be provided outside the fluid pressure device. For example, a port that communicates from the gas chamber and opens to the outer periphery of the cylinder tube is provided, and a pressure regulation path that communicates this port and the oil supply port is provided outside the fluid pressure device, and the pressure transmission device 3B is provided in the middle of the pressure regulation path. It only has to be attached.
[0045]
The cylinder tube 11, the rod 12, the rod bush 13, the rod cover 14, the head cover 16 and the pressure transmission device 3 are all made of a carbon steel material for machine structure. The container 31B of the pressure transmission device 3B is also made of a carbon steel material for machine structure. The bellows 32B is made of stainless steel.
[0046]
In the above-described embodiment, a method other than the method described above can be used as the method of forming the gap 132. The rod bush 13 and the rod cover 14 may be integrally formed as a rod cover, and the oil passage 22 that directly communicates the oil chamber 21 and the oil supply port 144 without providing the gap 132 may be provided.
[0047]
The position, size, shape, and the like of the oil chamber are not limited to those shown in the above-described embodiment. The number of first seal members and second seal members is not limited to one each, and a plurality of first seal members and a plurality of second seal members can be provided according to the scale, application, operating conditions, etc. of the fluid pressure device. In addition to the first seal member and the second seal member, for example, a dust seal or the like can be provided on the inner peripheral surface of the rod bush.
[0048]
In the pressure transmission device 3, another elastic body can be used instead of the spring 33. In addition, when the inner surface of the small cylinder tube 31 can be processed so that the small piston 31 slides satisfactorily, the spring 33 may not be provided.
[0049]
The shape, structure, and the like of the pressure transmission device are not limited to those shown in FIGS. 4 and 5 and may be configured to transmit the pressure of the gas on one side blocked by the transmission member to the oil on the other side. That's fine. The material of the transmission device is not limited to the carbon steel material for machine structure, and other materials can be used.
[0050]
In the above-described embodiment, the shape, structure, material, and the like of each part can be changed as appropriate within the spirit of the present invention. The present invention can be applied to various devices having a rod-like force transmission mechanism that has a pressurized gas inside a cylinder and reciprocates inside and outside the cylinder.
[0051]
【The invention's effect】
According to the present invention, in a fluid pressure device, a seal that improves the sealing performance between the inner peripheral surface of the through hole of the rod cover and the outer peripheral surface of the rod that slides on the inner peripheral surface and increases the durability of the seal member. An apparatus can be provided.
[Brief description of the drawings]
FIG. 1 is a front sectional view of a gas spring provided with a sealing device according to an embodiment of the present invention.
2 is an enlarged partial front sectional view showing a seal portion in FIG. 1; FIG.
3 is a cross-sectional view taken along the line AA in FIG.
4 is a front sectional view of a pressure transmission device that constitutes the sealing device of FIG. 1;
FIG. 5 is a front sectional view of another embodiment of the pressure transmission device.
FIG. 6 is a partial front sectional view of a gas spring provided with a conventional sealing device.
[Explanation of symbols]
1 Gas spring (fluid pressure equipment)
2 Sealing device 3, 3B Pressure transmission device 11 Cylinder tube 12 Rod 13 Cover (rod bush)
14 Cover (rod cover)
15 Gas chamber 21 Oil chamber 22 Oil passage 23 Pressure regulation passage 32 Small piston (transmission member)
32B Bellows (Transmission member)
133 Inner peripheral surface of through hole

Claims (4)

Fluid pressure in which a rod is movably inserted into a through hole of a cover that closes one end of the cylinder tube, and pressurized gas is sealed in a gas chamber formed inside the cylinder tube or pressurized gas is introduced. A sealing device for sealing the gas in the gas chamber in the through hole of the device,
An annular oil chamber provided on the inner peripheral surface of the through hole, a seal member provided on the inner peripheral surface of the through hole and sealing between the gas chamber and the oil chamber, and provided on the cover An oil passage communicating the outside of the cover and the oil chamber, a pressure regulating passage formed to communicate the oil chamber and the gas chamber, and the cover from the cover so as to block the pressure regulating passage. A pressure transmission device provided protruding from the gas chamber ,
The pressure transmission device includes a transmission member that is movable or deformable according to a differential pressure on both sides of the pressure regulating path that is blocked and blocked.
Oil is sealed in a side of the oil chamber, the oil passage, and the pressure adjusting passage that communicates with the oil chamber, and the gas pressure of the gas chamber is supplied to the oil chamber via the pressure transmission device. Configured to transmit to oil,
A sealing device for a fluid pressure device. The transmission member is
A piston that slides on a cylindrical inner peripheral surface,
The sealing device for a fluid pressure device according to claim 1. The transmission member is
A diaphragm or bellows,
The sealing device for a fluid pressure device according to claim 1. A fluid pressure device provided with the sealing device according to claim 1.

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