JPH07103362A - Valve surging preventing device - Google Patents

Abstract

PURPOSE:To prevent fault of surging and the like without following a sacrifice by automatically suppressing a self-excitation movement phenomenon of a coil shaped spring formed a valve body. CONSTITUTION:A buffer member 8 is provided on the fluid primary side range of a coil shaped spring formed a valve body for controlling the amount of a fluid passed between coils while changing the clearance between the coils. The buffer member 8 is provided in such a constitution that a seat plate 8a part is held on the upstream side spring seat part of the coil shaped spring 7 formed the valve body, and the free end of am impeller 8b part makes flow downstream The buffer member 8 is made of a soft elastic material. The twilled line 7a of each coil for the coil shaped spring 7 formed the valve body is pushed by means of suppressing force generated by the fluid pressure difference between the surface and the back surface of the nearly flat surface part of the impeller 8b so as to suppress respective selfish sliding motions of respective coils.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surging prevention device in a valve body portion of a valve (indicating a unit) for controlling fluid such as water, and more particularly, the valve body portion is composed of a coil spring. The present invention relates to a surging prevention device for a valve.

[0002]

2. Description of the Related Art Conventionally, a valve whose valve body is formed of a coil spring is used as a constant flow valve in Japanese Patent Application Nos. 5-4838 and 5-114965 disclosed by the present applicant. In addition, as a sluice valve, there is
Further, Japanese Patent Laid-Open No. 59-103084 is known as a thermostat valve.

[0003]

The secondary side, through which the fluid has passed through the gap between the windings of the coiled spring, which is the valve body, is in a state of severe turbulence. Particularly, when the wave of the turbulent flow has a periodicity, the periodicity causes the natural frequency of the coiled spring forming the valve element (ω = a√ (k / m), where a
Is a constant, k is a spring constant, and m is the mass of the spring), the spring may cause a self-excited vibration phenomenon due to resonance in the axial direction. It is believed that this vibration causes each coil of the coil-shaped spring that forms the valve element to oscillate, and also oscillates both spring seats to strike each other to generate an abnormal noise. So-called valve surging (SURGIN
G) It is a defect. This surging problem causes noise due to abnormal noise, which not only weakens the original function of the valve but also significantly shortens its life.

In the conventional product shown in the preceding paragraph, in advancing countermeasures against the above-mentioned surging problem, the natural frequency ω described above was variously shaken, and the harmony point was searched for by experiments. Is. However, this method has the following problems.

1) Japanese Patent Application No. 5-4838 and Japanese Patent Application No. 5-1
Regarding the constant flow valve of No. 14965, in order to maintain the constant flow valve function regardless of the fluctuation of the supply pressure, the spring constant k of the coiled spring forming the valve body needs to be limited to a certain width. Therefore, there is a limit to measures against the surging problem, and the best constant flow valve cannot be provided.

2) The shut-off valve disclosed in Japanese Utility Model Laid-Open No. 48-9421 and the thermostat valve disclosed in Japanese Patent Laid-Open No. 59-103084 have only an opening / closing function of the valve, which is an obstacle for changing the natural frequency. Is smaller than that in 1) above, but from experience, the direction of countermeasures against surging problems is that the spring constant k tends to settle toward the hard side with respect to the planned value.
For this reason, it is necessary to change the surrounding parts of the valve body including the valve housing to be strong and large, which results in high cost. Especially for thermostat valves, it is necessary to increase the capacity of the wax element, which is a temperature sensitive element.
Further, the cost becomes higher.

Conventionally, as described above, in order to take measures against the surging problem, the original function is reduced, and the surrounding parts are made strong and large, which increases the cost. Then, there was some sacrifice.

Therefore, an object of the present invention is to automatically suppress the above-mentioned self-excited vibration phenomenon of the coil-shaped spring forming the valve body, thereby preventing the above-mentioned surging failure without sacrificing. Another object of the present invention is to provide a surging prevention device for the valve.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is designed to change the interval between the windings of a coiled spring forming a valve body in a fluid passage, In a valve designed to control the amount of fluid passing through
In the fluid primary side region of the coiled spring that forms the valve element, and further, the free end of the blade portion of the cushioning member whose seat plate portion is clamped by the upstream spring seat portion of this coiled spring is located on the downstream side. The buffer member is provided so as to flow toward the outside, and the buffer member is made of a flexible elastic material, and is a coil-shaped spring that forms the valve body by a restraining force generated by a fluid pressure difference between the front and back surfaces of the blade substantially flat surface portion of the member. The ridge line of each of the windings is suppressed to suppress the independent swinging of each of the windings.

[0010]

In the primary side region of the fluid, the flexible blades of the cushioning member are arranged toward the downstream side along the ridgeline of each winding of the coiled spring forming the valve element. When the flow velocity of the fluid acts on the substantially flat surface portion of the blade, a suppressing force acts from the differential pressure between the front and back of the substantially flat surface portion toward the ridgeline of each winding of the coiled spring. Since this restraining force works in a distributed manner on each winding of the coiled spring forming the valve body, even when each winding reaches the natural frequency region of the same spring, the self-excited vibration phenomenon occurs. Does not cause
Therefore, it is possible to prevent the surging problem accompanied by abnormal noise.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a valve surging prevention device according to the present invention will be described below with reference to FIGS.

First, the first embodiment shown in FIGS. 1 to 3 will be described. This first embodiment shows a case where the surging prevention device of the present invention is applied to the constant flow valve in the example of the conventional product. FIG. 1 shows a vertical cross-sectional side view of the constant flow valve before use. FIG. 2 is a perspective view of a propeller-shaped cushioning member.

In FIG. 1, 1 is a water supply pipe line, 2 is a valve support casing provided so as to divide the inside of the water supply pipe line 1 at a right angle, 3 is a valve support plate, 4 is a bearing cylinder, and 5 is A spring bearing plate, 6 is a guide shaft integrated with the spring bearing plate, 7 is a conical coil spring that forms a valve body, and 8 is a buffer member whose details are shown in FIG.

The valve support casing 2 has a cylindrical shape for stabilizing the inside of the water supply pipe line 1, and is in contact with a step portion 1a in the water supply pipe line 1 toward the upstream side so as to be inside the annular groove 2a of the outer peripheral surface. A sealing member 2b such as an O-ring is attached to the inside of the water supply pipe 1 so as to have an airtight relationship. The valve support plate 3 which is provided integrally with the valve support housing 2 so as to divide the inside of the water supply conduit 1 at a right angle has a plurality of through holes 3a, 3a, ...

A guide shaft 6 having a spring receiving plate 5 is slidably and rotatably assembled in the bearing cylindrical body 4, and a space between the lower surface of the spring receiving plate 5 and the outer peripheral portion of the upper surface of the valve supporting plate 3 is provided. In addition, a conical coil-shaped spring 7 forming a valve body is provided. A retaining ring 6b is fitted in an annular groove 6a at the end of the guide shaft 6 protruding downstream from the bearing cylinder 4.
In this way, the valve support housing 2 including the spring receiving plate 5 and the conical coil-shaped spring 7 forming the valve body is directly assembled in the water supply conduit 1 so as to block the passage of the fluid.

Here, the cone-shaped coiled spring 7 forming the valve element has its small diameter side abutted against the lower surface of the spring receiving plate 5 and its large diameter side abutted against the outer peripheral portion of the valve support plate 3 upper surface. Moreover, it is in a slightly compressed state. Then, the pressure of the tap water flowing into the water supply conduit 1, that is, the primary pressure is the cross section of the guide shaft 6 of the spring receiving plate 5 and the upper surface of each winding of the conical coiled spring 7 forming the valve body ( (Corresponds to the upper surface of the spring wire development length) acts uniformly.

Further, the pressure receiving area A for controlling the valve opening and closing as a constant flow valve is maximum when it corresponds to the area of the upper surface of the valve support plate 3, and the operating form of the conical coil spring 7 forming the valve body. Of the winding starts to contact from the large diameter side and sequentially shifts to the smaller diameter side as the displacement amount increases, so that the winding diameter decreases substantially in proportion to the through hole area S described later. The constant flow valve allows the change in water pressure to be controlled by the pressure receiving area A as described above.
It is designed to detect and respond with. The conical coil-shaped spring 7 forming the valve element is formed in a spiral shape toward the small diameter side so that the windings of the conical coil spring 7 sequentially contact the inside of the large diameter side. It becomes a disc shape.

In the above constant flow rate valve, in the stable state of the flow rate control, the windings on the small diameter side of the conical coiled spring 7 forming the valve body are not in contact with each other, and a gap is maintained therebetween. . The total circumference of this gap becomes the passage hole area S that controls the fluid in this stable state. In addition, at the contact portion of each winding, the leakage of fluid from the contact surface is required to ensure the function as a constant flow valve. Further, the valve support plate 3 has a backup function of the conical coiled spring 7 that forms the valve body during the displacement as described above.

A conical coiled spring 7 forming this valve body
At the boundary, the fluid pressure changes from the primary pressure P1 to the secondary pressure P2. Then, with the differential pressure as ΔP and the fluid flow rate as Q, the conditions for controlling the constant flow rate are searched (for details, refer to Japanese Patent Application No. 5-4838 related to the proposal by the present applicant). It is Q∝S√ΔP. That is, the condition that the flow rate Q is constant is that the passage hole area S and the coiled spring 7 forming the valve body are
That is, the product of the square roots of the differential pressure (√ΔP) with respect to is constant. Therefore, the spring load characteristic of the coil spring 7 is set to a non-linear characteristic so as to satisfy this condition.

Next, the operation of the above constant flow valve will be described.
When the use of a hot water heater (not shown) is started and there is a fluid flow on the inlet side, the pressure receiving area A formed by the spring receiving plate 5 and the upper surface of the conical coil spring 7 forming the valve body
The supply pressure of the tap water acts on. As a result, the coiled spring 7 is pushed and its state changes.

That is, the coil-shaped spring 7 starts contacting from the large diameter side of the conical shape, and this contact progresses to the small diameter side and becomes a state close to full closure once. The reaction force generated by the displacement causes the valve to be pushed back toward the valve opening side. Then, the operation of pushing back to the valve closing side by the action of the pressure receiving area A is repeated, and the flow rate becomes stable at the set flow rate value. In reality, the repetition of this operation is completed instantly. In such a stable state, the above-mentioned formula is established, and the actual fluid is controlled and used according to the formula of its flow rate.

Here, the supply pressure of tap water is actually
There is 0.3~7.0kg / cm ² and variations, considering the state of the constant flow valve in the low-pressure side (0.3kg / cm ²⁾ as a problem, that the pressure acting on the pressure receiving area A is small ,
The amount of displacement of the conical coiled spring 7 forming the valve body is small, and it is predicted that this state is exactly close to the state shown in FIG. As is clear from FIG. 1, the winding gap of the coiled spring 7 is sufficient over each winding, and therefore the passage hole area S of the valve portion is the product of each winding gap and its circumferential length. Therefore, the number of valves is so large that it cannot be compared with the conventional constant flow valve. Therefore, in such a state on the low pressure side, the passage resistance of the fluid is small and the pressure loss is very small.

In addition, Japanese Patent Application No. 5-1 related to the applicant's proposal
In No. 14965, the conical coiled spring 7 forming the valve element is replaced by a shape memory alloy (SMA; Shape M).
It is made of the Emory Alloy) and its shape is memorized as the shape which is heat-treated on the elongation side. Thereby, there is an advantage that the hot water supply temperature can be always stabilized regardless of the time.

In the above constant flow valve, the buffer member 8
As shown in FIG. 2, a disc-shaped seat plate 8a having a propeller shape and a through hole 8c in the center, and the seat plate 8
The blades 8b and 8b extend in the radial direction from the periphery of a (in the illustrated example, two blades facing each other in the diametrical direction of the seat plate 8a). The vane 8b has a form that hangs toward the downstream side so as to follow the conical shape which is the ridge line 7a on the outer peripheral side of each winding of the conical coil spring 7.
When there is a flow velocity of the fluid, it is in a situation where it is easy to adapt to the ridge line 7a immediately.

The seat plate 8a of the buffer member 8 is sandwiched between the spring receiving plate 5 and the upstream (small diameter portion side) seat surface of the conical coil spring 7 forming the valve body, and Since the guide shaft 6 has a structure that penetrates the seat plate 8a (see the through hole 8c), the blades 8b, 8b do not shift even when subjected to a violent operation, and exhibit a stable function. Is provided. Since the cushioning member 8 is made of an elastic body such as a soft synthetic rubber and a synthetic resin, the cushioning member 8 is more easily fitted to the ridge line 7a on the outer peripheral side of the coiled spring 7.

FIG. 3 is a vertical sectional side view showing a stable state of the flow rate control. That is, since the fluid is flowing toward the downstream side, the blades 8b, 8 of the buffer member 8 are
b is a ridge line on the outer peripheral side of each winding of the coiled spring 7 under the pressure difference between the front side (which means the upstream side of the fluid) and the back side (which means the coiled spring side) of the substantially flat surface portion of the same blade. The suppressing force acts toward 7a, and is appropriately dispersed in each winding contacting each blade 8b, 8b.

The restraining force is a force by which each winding of the conical coiled spring 7 forming the valve body is allowed to freely swing when the natural frequency region of the spring is reached. It must have the ability to control.
There are the following three methods for adjusting the suppressing force.

1) Adjust the substantially flat surface area (length * width) of the blade 8b of the buffer member 8.

2) The number of blades 8b of the buffer member 8 is adjusted.

3) The above methods 1) and 2) are simultaneously adjusted.

By the above method, etc., the restraining force is
It is possible to select an appropriate one, and therefore, the suppression control of the natural frequency is easy.

Next, a second embodiment shown in FIGS. 4 and 5 will be described. The second embodiment shows a case where the surging prevention device of the present invention is applied to the sluice valve in the conventional example. FIG. 4 is a vertical sectional side view of the gate valve before use. FIG. 5 is a perspective view of a cushioning member having a round chair shape.

In FIGS. 4 and 5, 30 is a substrate, 50 is a sealing plate, and 70 is a coiled spring which forms a valve body.
70a is the ridgeline of each winding of the spring. Reference numeral 80 denotes a round chair-shaped cushioning member, 80a is an annular seat plate, and 80b is a blade.

The substrate 30 has a through hole 30a in the center thereof, and a sealing plate 50 is provided on the lower surface of the substrate 30 via a cylindrical coil spring 70 forming a valve body. When the primary side pressure of the fluid is less than a predetermined value, the windings of the cylindrical coiled spring 70 forming the valve body are in contact with each other and are held in the valve closed state, and the primary side pressure of the fluid reaches the predetermined value. When it exceeds this, the windings are separated from each other, and as shown in FIG. 4, the valve is opened to allow fluid to pass from the gap to the outer peripheral side.

In the above gate valve, the buffer member 80
As shown in FIG. 5, the circular seat plate 80a has a circular chair shape and has a through hole 80c in the center, and the seat plate 80a.
The blades 80b and 80b extend from the inner periphery of a in the radial direction (in the illustrated example, two blades facing each other in the diametrical direction of the seat plate 80a). The blade 80b has a shape that hangs toward the downstream side along the ridgeline 70a on the inner peripheral side of each winding of the coiled spring 70, and immediately when the flow velocity of the fluid is present, The ridgeline 70a is in a familiar state.

The seat plate 80a of the cushioning member 80 is sandwiched between the base plate 30 and the upstream seat face of the coil spring 70 forming the valve body, and is formed on the lower surface side of the base plate 30. Since the seat plate 80a is fitted in the recess 30b, the blades 80b, 80b are provided so as to exhibit a stable function without being displaced even when subjected to a violent operation. Similar to the first embodiment, the buffer member 80 is also made of an elastic body such as soft synthetic rubber and synthetic resin, so that it is easier to fit the inner peripheral side ridge line 70a of the coiled spring 70. It has become a thing.

In FIG. 4, since the fluid is flowing toward the downstream side, the blades 80b of the buffer member 80,
80b receives the differential pressure between the front and back of the substantially flat surface portion of the blade,
The restraining force acts toward the ridgeline 70a on the inner peripheral side of each winding of the coiled spring 70, and is appropriately dispersed in each winding in contact with each blade 80b, 80b.

Next, a third embodiment shown in FIGS. 6 and 7 will be described. This third embodiment shows a case where the surging prevention device of the present invention is applied to the thermostat valve in the conventional example. FIG. 6 is a vertical cross-sectional side view of the thermostat valve before the start of use. FIG. 7 is a partial cross-sectional perspective view of a round lid-shaped cushioning member.

In FIGS. 6 and 7, 200 is a valve support housing, 700 is a conical coiled spring that forms a valve body, and 700a is the ridge of each winding of the spring. 800 denotes a round lid-shaped cushioning member, 800a denotes an annular seat plate, 8
00b is a blade. A shaft-shaped member 900 shown in the center of FIG. 6 indicates a wax element which is a temperature sensitive element.

The valve support casing 200 is provided with a wax element 900 in the center and a plurality of through holes 200 around the wax element 900.
a, 200a, ...
The large diameter side of the conical coiled spring 700 forming the valve element is locked on the upper part of the. In addition, this coiled spring 700
The small diameter side of the piston 90 of the wax element 900
It is locked to 0a. As a result, the central portion of the coiled spring 700 is connected to the piston 900a of the wax element 900.
The coil-shaped spring 700 has the windings closely contacting each other when there is no load.

In this thermostat valve, when the temperature is low, the coiled spring 700 forming the valve body has a shallow conical shape, and the windings thereof are in close contact with each other to be in a closed state. When the temperature rises, the piston 900a projects from the wax element 900 and pushes up the central portion of the coil spring 700 to deform it into a deep conical shape. As a result, as shown in FIG. 6, a gap is formed between the windings, the fluid flows through the gap, and the valve is closed. The coil spring 700 may be made of shape memory alloy (SMA).

In the thermostat valve described above, as shown in FIG. 7, the cushioning member 800 has a circular lid shape and an annular seat plate 800a having a through hole 800c in the center.
And blades 800b and 800b extending from the inner circumference of the seat plate 800a in the radial direction (two in the illustrated example, which face each other in the diametrical direction of the seat plate 800a). The vane 800b has a shape that hangs toward the downstream side along the inner peripheral side ridge line 700a of each winding of the coiled spring 700, and when there is a fluid flow velocity,
Immediately, the ridge 700a is easily familiar with the ridge 700a.

The seat plate 800a of the cushioning member 800 is
Coil-shaped spring 7 that forms the valve body with the valve support housing 200.
No. 00 and the upstream side seating surface, and the seating plate 800 is inserted into the storage annular groove portion 200b formed in the valve support housing 200.
The blade 8 has a structure in which a is fitted.
00b and 800b are provided so as to exhibit stable functions without being displaced even when subjected to intense motion. The cushioning member 800 is also made of an elastic body such as soft synthetic rubber and synthetic resin, as in the first embodiment.
Familiarity with the ridge line 700a on the inner peripheral side of the coil-shaped spring 700 is further facilitated.

In FIG. 6, since the fluid is flowing toward the downstream side, the blades 800 of the buffer member 800 are
The blades 800b and 800b receive a differential pressure between the front and back surfaces of the substantially flat surface portion of the blade, and exert a restraining force toward the ridge line 700a on the inner peripheral side of each winding of the coiled spring 700, and the blades 800b and 800b.
It is properly dispersed in each winding in contact with 00b.

By the way, the cross-sectional shapes of the blades 8b, 80b, 800b of the cushioning members 8, 80, 800 of the above-described embodiment are those shown in FIGS. 8A to 8F. FIG. 8 (A) shows a standard shape, and FIG. 8 (B).
(F) is for improving the fluid resistance against the blades 8b, 80b, 800b, and shows a typical example in which the surface on the upstream side is projected. That is, in FIG. 8, (A) has a uniform thickness, (B) has a convex shape projecting to the front surface side, (C) has a substantially semicircular shape projecting to the front surface side, (D) Is a substantially mountain-shaped one that protrudes to the surface side,
In (E), the front side projects in an arc shape and the back side of the coiled spring side is recessed in an arc shape, and (F) is the front side projects in a substantially mountain shape and the back side is recessed in an arc shape.

Further, the shapes shown in FIGS. 8B to 8F are useful because they serve as reinforcements for the blades 8b, 80b, 800b when the cushioning members 8, 80, 800 are enlarged. Becomes The shapes shown in FIGS. 8 (E) and 8 (F) are coil-shaped springs 7, 70, which form a valve body that contacts the back surface.
The 700 side is arcuate so that the outer diameter or the inner diameter of the spring can be easily grasped, and the effect of the above-mentioned restraining force is further improved.

The method of arranging the valves to which the surging prevention device according to the present invention is applied, the kind of fluid for which the flow rate is to be controlled, etc. are arbitrary, and the number of blades of the buffer member is one or three. It is needless to say that the specific detailed structure such as one or more may be appropriately changed.

[0048]

As described above, according to the surging prevention device for a valve of the present invention, an inexpensive cushioning member made of a flexible elastic material is provided on the fluid primary side of the coiled spring forming the valve body of the valve. Since it is possible to prevent surging just by providing it, for example, in the case of a constant flow valve, it is possible to design with the best function as a constant flow valve without worrying about the natural frequency. Further, in the case of a sluice valve and a thermostat valve, the parts around the valve body including the valve housing can be designed rationally, and the cost can be reduced. Therefore, it is possible to provide a low-cost valve having the best function as a result.

[Brief description of drawings]

FIG. 1 shows a valve as an example to which the present invention is applied, and is a vertical cross-sectional side view of a constant flow valve according to a first embodiment in which a surging prevention device of the present invention is implemented, before use.

FIG. 2 is a perspective view showing a propeller-shaped cushioning member of the first embodiment.

FIG. 3 is a vertical sectional side view similar to FIG. 1, showing a stable state of the fluid control according to the present invention.

FIG. 4 is a vertical cross-sectional side view of a sluice valve according to a second embodiment in which a surging prevention device of the present invention is implemented, before use.

FIG. 5 is a perspective view showing a cushioning member having a round chair shape according to a second embodiment.

FIG. 6 is a vertical cross-sectional side view showing a thermostat valve according to a third embodiment in which the surging prevention device of the present invention is implemented, before use.

FIG. 7 is a partial sectional perspective view showing a round lid-shaped cushioning member of a third embodiment.

FIG. 8 shows a cross-sectional shape of the blade of each cushioning member of the above-described embodiment, (A) is a cross-sectional view of a standard shape,
(B), (C), (D), (E), (F) are cross-sectional views of a typical example in which the improvement of the fluid resistance against the blade is measured.

[Explanation of symbols]

 1 Water Supply Pipeline 2,200 Valve Support Housing 3 Valve Support Plate 4 Bearing Cylindrical Body 5 Spring Catch Plate 6 Guide Shaft 7,70,700 Coil Spring 7a, 70a, 700a Forming Valve Body Ridge Line 8, 80,800 Cushion Member 8a, 80a, 800a Seat plate 8b, 80b, 800b Blade 30 Substrate 50 Sealing plate 900 Wax element

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeyuki Fujiyama 1-6-8 Fukamihigashi, Yamato-shi, Kanagawa Within Fuji Seiko Co., Ltd. (72) Takachi Tamiya 1-6-8 Fukamihigashi, Yamato-shi, Kanagawa Prefecture Issue Fuji Seiko Co., Ltd. (72) Inventor Hidenao Nagahama 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu City, Fukuoka Prefecture Totou Equipment Co., Ltd. (72) Inventor Akihiko Kiba 2 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka 1-2-1 Totoki Equipment Co., Ltd. (72) Inventor Katsuhiro Kawahara 2-1-1 1-1 Nakajima, Kokurakita-ku, Kitakyushu City, Fukuoka Prefecture Totoki Equipment Co., Ltd.

Claims (1)

[Claims] 1. A valve which is installed in a fluid passage and which controls the amount of fluid passing between the windings of a coiled spring forming a valve body by changing the spacing between the windings, In the fluid primary side region of the coiled spring that forms the valve body, a seat plate portion that is sandwiched by the upstream spring seat portion of this coiled spring,
A cushioning member having a vane portion whose free end extends toward the downstream side from the seat plate portion is arranged, and the cushioning member is formed of a flexible elastic material, and the vane portion has a substantially flat plane. A restraining force generated by the fluid pressure difference between the front and back sides of the part holds down the ridgeline of each winding of the coiled spring forming the valve body to suppress the swinging of each winding. Surging prevention device.