JPH06329313A - Self-excited vibration control method in fluid floatation - Google Patents

Abstract

PURPOSE:To effectively conduct the vibration control without a special device for self-excited vibration due to compressive fluid in a static pressure generating type floating bearing using an air curtain. CONSTITUTION:In a fluid floating device including plural jet slits 1, 2 for generating static pressure in a floating clearance part, which can be selected according to the dimensions of a floating object 10 to increase the use efficiency of a fluid and attain high practicality, a bad influence on vibration stability by the internal header capacity which becomes a dummy in the case of a large floating object 10 can be prevented by forcing a small bias flow to flow out from the internal header B to largely reduce a coefficient of flow. Further, it is possible to effectively control the self-excited vibration of the floating object 10 without addition of an extra device and large energy margin of a compressive fluid supply source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a plurality of ejection ports (or slits) communicating with a supply source of a compressive fluid, and selects the ejection ports (or slits) according to the area of a floating object as a target. And eject a compressible fluid such as air or nitrogen,
Due to the curtain sealing effect of the fluid, a fluid levitation device that generates static pressure between the levitation object and the levitation device to levitate the object, for example, a fluid levitation device that levitates and conveys a strip-shaped steel plate, etc. The present invention aims to improve the stability of self-excited vibration of a fluid levitation device.

[0002]

2. Description of the Related Art With the demand for high surface quality of band-shaped products and high-speed processing, a fluid levitation device capable of carrying a band-shaped product in a non-contact manner has attracted attention and has been actively used in recent years. FIG. 5 shows that the size of the floating object changes.
From the plurality of jetting slits, the jetting slit that matches the size of the floating object is selected to jet the fluid, so that the utilization efficiency of the fluid is improved. JP-B-58-39005 and 61-86455. 1 is a cross-sectional view of a known air curtain type fluid levitation device of Japanese Patent Laid-Open Publication No. 1993-331, in which the compressible fluid sent to a header B from a compressible fluid supply source device (not shown) is shown on the left side when the width of the floating object 10 is narrow. The fluid is ejected from the nozzle slit 1 like half and collides with the levitating object 10 to change its direction. Due to this momentum change, static pressure is generated in the area A sandwiched by the nozzle slit 1 When the floating object 10 is large and wide, as shown in the right half of the figure, the fluid is jetted from the nozzle slit 2 to generate static pressure in a wider area than when it is narrow. It is adapted to obtain a large floating force.

In these levitation devices, the balance of the part where the levitation static pressure is generated is subject to disturbances such as tension fluctuations in the strip-shaped steel sheet carried by the levitation object 10 and the compressible fluid. Even in the supply source device, minute pressure fluctuations are always unavoidable, so self-excited vibrations may occur due to these disturbances, and the levitating object is heavy. This occurred remarkably when the outer ejection slits were selected and levitated by the levitation device having a structure in which the matching ejection slits were selected to eject the fluid. If this happens, normal transportation cannot be performed.Currently, as a countermeasure for this, the levitation condition and the operating condition of the line are empirically changed, or a device for vibration damping is added to the strip steel plate transportation line. Then, the actual situation is to suppress the vibration generation to the extent that it does not hinder the transportation of the strip-shaped steel sheet.

Further, as seen in Japanese Examined Patent Publication No. 3-249423 and Japanese Examined Patent Publication No. 3-249424, in a pocket type static pressure bearing, it is necessary to reduce the pocket volume while securing the area of the pressure receiving portion. In addition, there are some inventions that improve the stability of self-excited vibration and other characteristics. Furthermore, the Japan Society of Mechanical Engineers Proceedings (Part 3), Volume 32, 2
No. 44 (Sho 41.12) P. As shown in the research results of the vibration stabilizing element by Mori et al., 1877-1882,
There is a device to stabilize the vibration by providing a fluid resistance element and a stabilization chamber in the part connected to the bearing pocket, but the air curtain type fluid levitation device is structurally different from the pocket type because of its stability. The improvement method cannot be applied.

[0005]

As described above, in a device that levitates an object by generating a static pressure between the levitating object and the levitating device by supplying the compressive fluid, self-excited vibration caused by the compressible fluid. It is an important issue to suppress self-excited vibration in a wide floating object of a fluid levitation device with high practicality, which has multiple ejection slits and makes it possible to select these slits to improve fluid utilization efficiency. The suppression of is an important issue.

The conventional vibration suppression measures used in the air curtain type fluid levitation device require a great deal of labor to search for stable operating conditions and also cause operational restrictions. Since a large margin had to be taken, there was a lot of wasted energy, and the method of adding a device for damping vibration in the transport line to suppress the occurrence of vibration requires the provision of a special device for this purpose. ,And,
Since extra tension is applied to the operation, there is a problem that it is difficult to use it as a levitation device that conveys wide strip-shaped products. On the other hand, the vibration suppression measure in the pocket type levitation device cannot be applied to the air curtain type fluid levitation device, and its application effect is insufficient.

It is an object of the present invention to provide a method capable of effectively suppressing the occurrence of self-excited vibration in a floating object during the above-described fluid levitation.

[0008]

Therefore, the present inventor has found the following invention by analyzing the fluid balance and vibration characteristics of the fluid levitation device and experimentally clarifying the vibration characteristics. That is, the present invention relates to the floating surface area of the target floating object from the outer ejection port (or slit) or the inner ejection port (or slit) communicating with the supply source of the compressive fluid, A fluid is ejected by selecting one of the ejection ports (or slits) to form a region between a pair of ejection ports (or slits) from which the fluid is ejected, or a closed curve is formed. Select in order to generate static pressure by selecting a jet port (or slit) when a static pressure is generated between the floating object and a floating object in the area surrounded by the jet port (or slit). Spout (or slit)
It is characterized in that the compressive fluid is caused to flow also into the ejection port (or slit) located on the inner side to suppress self-excited vibration of the floating object.

[0009] It should be noted here that when the outer outlet (or slit) is selected to generate static pressure, the volume related to the inner outlet (or slit) that is not used is not vibrated. It has a great impact on stability. The present invention reduces the occurrence of self-excited vibration by biasing the flow rate of the compressive fluid against the adverse effect of this volume, stabilizes the vibration, and suppresses the vibration.
The compressible fluid here corresponds to a gas body such as air.

[0010]

When the fluid balance and vibration characteristics of the fluid levitation device are examined with a macro transfer function, the levitation height H against the fluctuation of the force F (external force or pressure ... If the area is fixed, the handling can be the same) Since we are discussing the stability, let the Laplace transfer function be Ω (Laplace operator s)

[Equation 1] The stability of the system can be analyzed by examining the property of the denominator Ω _h (s) of.

From equation (1), Ω _f (s) × force = Ω _h (s)
× Since the flying height is established, if the mass flow rate is taken as the balance amount common to the left and right sides, Ω _f (s) is composed of the mass flow rate of the numerator and the force dimension of the denominator, and Ω _h (s)
In (s), the numerator should be composed of the mass flow rate, and the denominator should be composed of the flying height.

Now, consider Ω _h (s) × flying height. Since it is a vibration problem, the force M (d ² h / d ² t) generated by the inertia M is Ms ² ·
Therefore, when the flow rate balance point Q is linearized and the representative amount of force is the pressure P, the mass flow rate fluctuation amount q is represented.

[Equation 2]

When the integral element of the flow rate exists in the diameter, the one-time integral of the mass flow rate fluctuation amount q becomes the integral element mass K _I. Therefore, letting the flow coefficient including the pressure function be C _q , K _I = C _q q dt (3) Therefore, when the relationship between the integral element K _I and the mass flow rate q is displayed in Laplace, q = K _I s. Considering this, the numerator of equation (2) has a first-order lag in the flow constant term K _Q. By adding the term K _I · s,

[Equation 3] The equation (4) is a form in which the term of the force of the transfer function of the second-order viscous damping vibration response that is often seen has a first-order lag, and the Hurwitz stability condition is shown by the following equation (5). 2ζω _n −τ ₁ · ω _n ² ≧ 0 (5) That is, the first-order lag of the force, that is,

[Outer 1] Becomes larger, τ ₁ becomes larger, which means that the negative term in Eq. (5) becomes larger, resulting in unstable vibration.

Here, considering K _I1 , since K _I1 is proportional to the volume V and the flow coefficient C _q that are the base of integration, K _I1 can be reduced by the inner ejection slit to stabilize the vibration. There are two ways to reduce the volume V involved and the flow coefficient C _q . It is ideal if the volume V related to the inner ejection slit can be made sufficiently small, but it is also important to reduce the flow coefficient C _q because there is a limit in order to make the flow uniform and secure the flow passage area. That is, since the original equation (2) that derives the stability determination equation (5) is linearized at the balance flow rate point, it is considered to reduce the first-order delay of the force at this balance point.

The jetting of the compressive fluid from the slit is an isentropic jet, and the flow rate change with respect to the pressure change is S _Q1 = {1- (P _o / P _i ) ^{(1-1 / K)} } ^1/2

[Equation 4]

The expression (6) means the tangent line of the pressure difference-flow rate curve shown in FIG. 4, but since it is a non-linear function, as can be seen from the figure, it shows a very large slope at the balance point a where there is almost no pressure difference ( The flow rate coefficient _Cq is large), the pressure difference increases, and the balance point b at which the flow rate corresponding to the pressure difference flows is small (the flow rate coefficient _Cq is small). That is, in the right half of FIG. 2, when the outer jet slit 2 is selected according to the area of the floating object 10, the volume V1 of the inner header B1 related to the inner jet slit 1 becomes the volume of K _I1 and therefore the vibration is not generated. This is a factor of stability, but at this time, when the flow control valve 31 is completely closed, the pressure in the internal header volume V1 becomes almost the same as the levitation static pressure P _A, and there is almost no pressure difference across the slit. Therefore, the state is close to the balance point a shown in FIG. 4, and there is a very large primary delay. On the other hand, when a certain amount of flow rate is flown without completely closing the flow rate control valve 31, a pressure difference commensurate with the flow rate is generated, so that the balance point b shown in FIG. 4 is reached and the flow rate coefficient C _q can be reduced. As a result, the primary delay of the force at the balance point is reduced, and vibration can be stabilized. In consideration of operability, the bias flow rate is preferably set so that the differential pressure from the floating static pressure is equal to or higher than 2 mmAq.

As described above, in the self-excited vibration suppressing method for the fluid levitation device according to the present invention, the bias flow rate is made to flow when the outer ejection slit is selected from the plurality of ejection slits in order to levitate a floating object having a large area. Inner header volume V
Since the flow rate coefficient of 1, that is, the first-order lag of the force can be reduced to reduce the vibration instability influence coefficient (τ _{1 in} equation (5)), a plurality of ejection slits are provided in order to increase the fluid utilization efficiency. A highly practical fluid levitation device has a great effect on suppressing its self-excited vibration, and even if the levitation amount of a floating object fluctuates due to some disturbance, it is easy to suppress self-excited vibration and perform stable fluid levitation device operation. be able to.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed description will be given below with reference to the drawings. FIG. 1 is a flow rate control flow chart for suppressing vibration of the fluid levitation apparatus of the present invention. First, a narrow or wide ejection slit is selected according to the size of the floating object. In the case of a narrow width, the flow rate control valve 31 controls the flow rate according to the floating condition, and the flow rate control valve 32 of the outer ejection slit 2 is closed because it wastes energy even if ejected, and in this case, it is conventionally performed. Perform exactly the same operation as the fluid levitation device.
If a wide width is selected, the flow rate control valve 32 of the outer ejection slit 2 controls the flow rate in accordance with the floating condition, and the flow control valve 31 of the inner ejection slit 1 is not completely closed. If the vibration of the levitating object 10 is confirmed by opening so that the flow rate is biased slightly, and if this vibration suppression is further required, the flow control valve 31 is opened a little further and the vibration of the levitating object 10 is within the target value. Adjust this until suppressed.

FIG. 2 is a sectional view of an embodiment of the fluid levitation device of the present invention, showing a state in which a narrow floating object 10 is levitated in the left half and a wide floating object 10 is levitated in the right half. It shows in the state. First, the description will be given in the left half of the ascending state of the narrow width. In this state, the ejection slit 1 corresponding to the narrow width is
Is selected, the valve 31 connected to a compressible fluid supply source (not shown) is opened to an appropriate amount necessary for floating, and the sent fluid enters the header chamber B1 and is ejected from the ejection slit 1 to A static pressure is generated in the portion and flows out from the floating gap portion, but the valve 3 corresponding to the wide ejection slit 2
2 is closed and there is no levitation control flow in the wide header chamber B2. In this state, the outer header volume V2 exists as a dummy volume, but since the levitation static pressure is generated in the portion A, it has almost no relation to the pressure, and the first-order lag of the force is zero, so this volume V2 is unstable in vibration. Not a factor.

Next, in the state where the size of the floating object is changed and the wide floating object 10 is levitated, that is, in the right half of FIG. 2, the jet slit 2 corresponding to the wide width is selected and not shown. Valve 32 connected to a source of compressive fluid
Is opened by an appropriate amount necessary for floating, and the sent fluid enters the header chamber B2 and is ejected from the ejection slit 2,
Although a static pressure is generated in the portion A and flows out from the floating gap portion, an inner header volume V1 corresponding to the ejection slit 1 corresponding to the narrow width exists as a dummy volume, and this inner header volume V1 functions as K _I1 . Therefore, the volume V1 may cause a vibration instability, but since the flow rate control valve 31 is opened so as to allow a slight flow rate 1 ', the flow rate coefficient when the flow rate control valve 31 is completely closed. It is much smaller, and the first-order lag of the force related to the inner header volume V1 is small, and vibration instability is prevented.

Further, the larger the bias flow rate flowing from the inner slit 1, the more effective is vibration stabilization. However, since the energy required to flow the fluid also increases, the oblique line shown in FIG. Area of
It is practically effective that the pressure difference from the levitation static pressure P _A is not more than the flow rate corresponding to 10 mmAq. The flow control valve 3
The flow rate control system considering the selection algorithms of 1, 32 and the various conditions of the floating object 10 is not related to the essence of the present invention, and therefore the description thereof is omitted.

The results of an experimental investigation on the effects of the present invention are shown in FIG. This is an experimental result of a strip steel sheet having a strip width of 1 m and a load of 60 kg loaded in a 1.2 m radius on a levitation device that turns 180 degrees shown in the bird's-eye view, but 0.3 m without the method of the present invention. compared to FIG inside header volume of ³ led the floating static pressure generator with closed flow control valve 31 3 (a), was flushed with bias flow corresponds 5mmAq the inner header in the present invention FIG. 3 (b) It can be seen that, except for a slight pressure fluctuation caused by the air flow, almost no vibration is generated, and even if a small amount of vibration is generated, it is immediately attenuated. Even in a fluid levitation device in which the number of jetting slits is set to four or more, and two or more slits are simultaneously selected to accommodate the width, the method of the present invention can reduce the volume of the inner header portion connected to the static pressure generating portion. It goes without saying that it exerts the effect of alleviating the adverse effects of vibration.

[0023]

As described above, according to the present invention, a highly practical air curtain type fluid levitation device having a plurality of ejection slits, which can be selected to improve the fluid utilization efficiency. In addition, the addition of extra equipment,
Without the energy margin of a large compressible fluid source,
Self-excited vibration due to compressible fluid can be easily suppressed, and its application effect is very large.

[Brief description of drawings]

FIG. 1 is an operation selection flowchart of the present invention.

FIG. 2 is a sectional view of a floating header for explaining the application of the present invention.

FIG. 3 is a comparison diagram of measurement results of vibration waveforms with and without the present invention.

FIG. 4 is a relationship diagram between a pressure difference and a flow rate.

FIG. 5 is a cross-sectional view of a conventional fluid levitation device.

FIG. 6 is a diagram showing a relationship between a pressure difference and a flow coefficient change rate.

FIG. 7 is a bird's-eye view showing a fluid floating state in the case of 180-degree turn.

[Explanation of symbols]

 A Static pressure generation part B1, B2 Header chamber 1 Narrow jet slit 2 Wide jet slit 10 Levitating object 11 180 degree turn Fluid levitation device header 31, 32 Flow control valve

Claims (1)

[Claims] 1. A jetting device according to a floating surface area of a target floating object from an outer jetting port (or slit) or an inner jetting port (or slit) communicating with a supply source of a compressive fluid. A region between a pair of jet ports (or slits) from which fluid is jetted, or a jet that forms a closed curve, by selecting one of the jet ports (or slits) to jet the fluid In the area surrounded by the outlet (or slit), when the static pressure is generated between the floating object and the object to levitate, the jet port (or slit) is selected to generate the static pressure. A method for suppressing self-excited vibration in fluid levitation, characterized in that a self-excited vibration of a levitating object is suppressed by causing a compressive fluid to flow also into the spout (or slit) inside the spout (or slit).