JPH0330735B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) The present invention relates to an air spring device used for vibration isolation tables and the like. (Technical Background of the Invention and Problems thereof) For example, in optical devices, even minute vibrations transmitted from the surroundings cause various operational troubles. Therefore, these devices are used by being placed on a so-called vibration isolating table designed to isolate external vibrations. An air spring device is used to support the table of this vibration isolation table. This air spring device has a structure as shown in FIG. 2, for example. That is, this device is composed of a load receiving plate 1 for supporting a table (not shown) to be supported, and an air chamber 3 located below the load receiving plate 1 and supporting it via a diaphragm 2. ing. This air chamber 3 is composed of a gap 4 sandwiched between the load receiving plate 1 and the diaphragm 2, and an additional tank 5 disposed below the diaphragm 2.
The gap 4 and the additional tank 5 are configured to communicate through an orifice 7. Further, the additional tank 5 is placed on the floor surface 8 with a vibration-proof rubber 9 interposed therebetween. According to the air spring device having such a configuration, the vibration of the floor surface 8 is attenuated and blocked by the vibration isolating rubber 9 and the air chamber 3, and transmission to the load receiving plate 1 is prevented. The resistance of the air sealed in the gap 4 and the additional tank 5 as it passes through the orifice 7 provides a vibration damping effect. FIG. 3 shows an example in which this orifice is taken out to the outside and the gap 4 and the additional tank 5 are connected by a pipe 11. A variable orifice valve 12 such as a speed controller is provided in the middle of this pipe 11. By adjusting the variable orifice valve 12, the damping effect described above is controlled. By the way, the performance of the air spring device for the vibration isolation table as described above is evaluated as follows. FIG. 4 shows a graph showing the relationship between the vibration frequency of the floor surface on which the air spring device is installed and the vibration transmission rate at which the vibration is transmitted to the load receiving plate of the air spring device. The unit of floor vibration frequency is Hz, and the unit of vibration transmissibility is dB. Here, if the natural frequency determined by the spring constant and supporting weight of this air spring device is ω _o , then the vibration transmissibility at this frequency is the maximum value, and the vibration transmissibility gradually decreases toward both sides. . The cross-hatched area in the figure where the vibration transmissibility is 0 dB or more is the amplification region, where vibrations from the floor are amplified and transmitted to the load receiving plate.
In addition, the hatched area in the figure where the vibration transmissibility is 0 dB or less is the vibration isolation effect area, and in this area, vibrations from the floor are attenuated and transmitted to the load receiving plate. Note that this vibration transmissibility is generally calculated as follows. That is, in a model of a one-degree-of-freedom (m-c-k) system, when the floor has a displacement amplitude of u=Asin ωt, the equation of motion of this system is as follows. mx¨+cx〓+kx〓=cu〓+ku Therefore, the vibration transmissibility of displacement Tr=x/A can be obtained by the following formula. ξ=c/c _c : Damping constant ratio C: Damping constant c _c : Critical damping constant = 2√ ω _o : Angular natural frequency of the system = (2πfn) ω: Angular frequency of the floor Now, in general, A high performance air spring device is required to have the following characteristics: (1) The natural frequency ω _o is low and the frequency at which the vibration isolation effect begins is low. This is because if ω _o is low, it is expected that vibrations can be isolated over a wider range than other existing vibrations. (2) Low resonance magnification. In other words, appropriate damping is obtained. If the dominant frequency of floor vibration (the vibration frequency unique to the floor that is most easily transmitted to the floor) and the natural frequency ω _o of the air spring device match, the resonance phenomenon will increase the floor vibration by several times to ten times. It is transmitted several times to the load receiving plate. Therefore, it is desirable to apply damping to suppress this resonance as much as possible. Here, Fig. 5 shows the actually measured values of the vibration acceleration of the load receiving plate when the air spring device with the characteristics shown in Fig. 4 is used and the predominant frequency of floor vibration is different. . In this graph, the horizontal axis represents the vibration frequency of the floor surface, and the vertical axis represents the vibration acceleration of the load receiving plate. In the case of FIG. 5a, when the dominant frequency of the floor vibration and the natural frequency of the air spring device both match at _ωo , a large vibration acceleration is generated as shown by the broken line. In addition, in the case of Fig. 5b, the dominant frequency _ωo ' of the floor vibration is greatly different from the natural frequency _ωo of the air spring device, so the increase in vibration acceleration is suppressed as shown by the broken line. There is. In both cases, the hatched area is the area exhibiting the vibration isolation effect. FIG. 6 is an explanatory diagram showing changes in vibration acceleration when floor vibrations of a certain predominant frequency are applied to air spring devices having various characteristics. First, FIG. 6a shows the characteristics of an air spring device having a natural frequency _ωo substantially similar to that shown in FIG. For this air spring device, if the dominant frequency of floor vibration is ω _o , then as shown in d of the same figure,
A large peak as shown by the broken line can be seen in the vibration acceleration. This is as shown in Figure 5a. Next, FIG. 6b shows the air spring device shown in FIG. 6a in which the vibration transmissibility near the natural frequency ω _o is sufficiently suppressed. For an air spring device with such characteristics, the dominant frequency of floor vibration ω _o
When vibration is applied, a certain peak occurs in the vibration acceleration as shown by the broken line, as shown in figure e, but the peak value is slightly lower than that shown in figure d. FIG. 6c shows this air spring device in which the natural frequency ω _o ' is shifted to a higher value. When floor vibration with the dominant frequency ω _o is applied to such an air spring device, as shown in Figure f,
The peak of vibration acceleration is kept sufficiently low as shown by the broken line. As explained above, the vibration isolating effect of an air spring device is determined by keeping the maximum value of its vibration transmissibility sufficiently low [as shown in Figure 6b], or by reducing its natural frequency to that of the floor surface. It can be seen that it is desirable to have a design that is different from the dominant frequency. However, the design concept of making the natural frequency of the air spring device different from the predominant frequency of floor vibration of the floor surface has the following problems. (1) Before designing an air spring device, the vibration transmission characteristics of the air spring device cannot be determined unless the vibration state of the floor is measured and its dominant frequency determined. This is not realistic as it requires different designs of the device depending on the location of use. (2) Since it is technically difficult to shift the natural frequency of the air spring device to a lower frequency, for example, 1 Hz or less, it is actually shifted to a higher frequency, as shown in Figure 6c. I will let you do it. However, if this is done, the inherent vibration isolation performance of the air spring device will be lowered compared to the cases shown in FIGS. 6a and 6b. That is, the vibration isolation effect region marked with hatching in the figure shifts to the right, resulting in a decrease in performance. (3) When floor vibration has a low frequency, for example a predominant frequency of about 4 Hz, it is technically very difficult to completely include this vibration in the vibration isolation area. In other words, as mentioned earlier, it is technically difficult to bring the natural frequency as close to 0 as possible, and the lower the natural frequency, the lower the support rigidity k of the device supporting the load receiving plate. becomes smaller,
This is because the load receiving plate may sway by itself in response to external force. Therefore, as shown in FIG. 6b, it can be seen that the design concept of reducing the peak of the vibration transmissibility is more realistic. A method for damping this peak is to increase the vibration damping effect. FIG. 7 shows an example of a conventional air spring device that enhances such a damping effect. In the figure, this device employs a structure in which an additional tank 5 placed under a load receiving plate 1 is suspended within a container containing a viscous fluid 14. This container is composed of an outer wall 15, a bottom plate 16, and a top plate 17. This top plate 17 has a shaft 18
A hanging bottom 19 is suspended by. As the viscous fluid 14, for example, silicone oil is used. As the shaft 18, for example, a steel rod is used. In this way, the air spring device can be attached to the hanging bottom 1.
9, a damping effect is added to the vibration of the air spring device by the viscous fluid 14. FIG. 8 shows a graph of the damping effect of the air spring device. This graph shows the vibration frequency of the floor on the horizontal axis.
The vertical axis shows the vibration transmissibility. As you can see from this graph, the viscosity ζ of the viscous fluid is 0.01~
As the value increases to 0.5, the vibration transmissibility gradually decreases. Further, even if the vibration transmissibility decreases due to a change in the viscosity of the viscous fluid, its natural frequency remains unchanged. In this way, by reducing the vibration transmissibility even if the natural frequency does not change, a sufficient damping effect can actually be obtained. Moreover, there is a greater advantage in design if the natural frequency is kept constant. On the other hand, the fact that such sufficient damping can be obtained means that floor vibrations are sufficiently damped and not transmitted to the load receiving plate, and it also has a good vibration damping effect when the load receiving plate itself vibrates. . Considering the region where this damping constant is smaller than 1, the greater the damping effect, the shorter the time required to stop the motor. This can be easily understood from the following equation. That is, the right side of the equation of motion for the one-degree-of-freedom system shown above is set to zero. mx¨+cx〓+kx=0 Find a general solution of this equation in the region where ξ=c/c _c <1. x=exp{−ξω _o t(Acosω _d t+Bsin ω _d t)}ω _d =ω _o √1− ^2If this general solution is schematically drawn as time domain data, it will look like Figure 9, and the damped oscillation The change in the envelope can be clearly seen. That is, FIG. 9b shows a case where the attenuation constant is smaller than FIG. 9a. Note that since the actual vibration isolation table is movably supported in the vertical and horizontal directions, it is preferable to provide sufficient damping characteristics in each direction. Returning now to FIG. 2, the air spring device shown in FIG. 2 uses an orifice 7 to provide its damping effect. In order to enhance the damping effect, the diameter of the orifice may be made smaller. However, if the diameter of the orifice is narrowed too much, the flow of air from the gap 4 to the additional tank 5 will be poor, and there is a risk that it will not work effectively for low natural frequencies. Furthermore, although this device is designed to reduce the natural frequency of vibrations in the horizontal direction by sandwiching a vibration isolating rubber 9 between it and the floor surface 8, the damping effect of the orifice 7 does not work in the horizontal direction. Therefore, if the damping of the vibration isolating rubber 9 is small, a sufficient damping effect cannot be obtained. Further, in the device shown in FIG. 7, a damping effect is obtained by using the high viscosity viscous fluid 14. However, the hanging bottom 19 is suspended by the shaft 18, and the shaft 18 only contributes to lowering the natural frequency in the horizontal direction. Therefore, the viscous fluid 14 imparts a damping effect only to vibrations in the horizontal direction. That is, with regard to the damping effect of vertical vibrations, as long as an orifice is employed, the same drawbacks as explained with reference to FIG. 2 exist. FIG. 10 shows an example of an air spring device that achieves damping in the horizontal and vertical directions using viscous fluid. In this device, a load receiving plate 1 is supported by a diaphragm 2, and this diaphragm 2 is connected to an outer ring 21.
It is supported by being sandwiched between the washer 22 and the washer 22.
This washer 22 is supported in an air chamber 25 surrounded by side walls 23 and a bottom plate 24.
Further, a support column 27 is planted in the center of the bottom surface of the load receiving plate 1, and a hanging plate 28 is fixed to the lower end of the support column 27.
This suspension plate 28 is provided with several through holes 29, and a damping plate 30 is provided on the upper surface thereof.
is fixed. A viscous fluid 26 is accommodated below the air chamber 25 . In such a device, whether the load receiving plate 1 vibrates vertically or horizontally, the viscous fluid 26
The damping plate 30 inside the viscous fluid 26
A certain damping effect is given by the force of. However, since such a device is supported by the diaphragm 2, although it is possible to reduce the natural frequency in the vertical direction, it is not possible to achieve a sufficiently low natural frequency in the horizontal direction. . In order to solve this problem, as shown in FIG. It can also be configured. The configuration of the other parts inside the air chamber 25 is as follows.
It is similar to the one shown in the figure. However, with such a configuration, the viscous fluid 26 cannot provide a sufficient damping effect to horizontal vibrations caused by the vibration isolating rubber 32. (Object of the invention) The present invention has been made focusing on the above points,
Aiming to lower the natural frequency in the vertical and horizontal directions,
Furthermore, it is an object of the present invention to provide an air spring device that provides a damping effect whose characteristics can be individually and independently adjusted in both the vertical and horizontal directions. (Summary of the Invention) The air spring device of the present invention includes a load receiving plate 41 on which an object to be supported is placed, and a flexible sealing material 61 that is placed below the load receiving plate 41 and supports the load receiving plate 41. , an air chamber 50 that elastically supports the load receiving plate 41 in a vertically movable manner;
a rod-shaped member 45 that directly or indirectly supports the load receiving plate 41 and elastically supports the load receiving plate 41 so as to be movable mainly in the horizontal direction, and a member that accommodates the viscous fluid 55 and is connected to the load receiving plate 41. a horizontal damping tank 57 that receives a part of the member and suppresses and damps its horizontal vibration; It is characterized by being equipped with a vertical damping tank 58 that suppresses and damps the vibration. (Embodiment of the invention) FIG. 1 is a longitudinal sectional view showing an embodiment of the air spring device of the invention. In the figure, this device has a rod-shaped support column 42 erected on the lower center surface of a load receiving plate 41. An internal bottom plate 43 is fixed to the lower end of this support column 42 . The internal bottom plate 43 is suspended by a rod-shaped member 45 that is inserted into a through hole of the top plate 44 and fixed. The top plate 44 and the inner washer 46 sandwich a flexible sealing material 61 between them. The top plate 44 and the inner washer 46 are connected by bolts 62.
are tightened and integrated. This flexible sealing material 61 is constituted by, for example, a diaphragm or a velophram. Further, the outer peripheral portion of this flexible sealing material 61 is sandwiched between an outer ring 47 and an outer washer 48. Outer ring 47 and outer washer 48
are integrally tightened with bolts 63. An air chamber 50 surrounded by an outer wall 51 and an outer bottom plate 52 is arranged below the outer washer 48. Also, inner washers 4
A horizontal damping tank 57 surrounded by an inner wall 53 and an intermediate bottom plate 54 is provided on the lower side of the tank 6 . Note that a vertical damping tank 58 is provided below the air chamber 50. The horizontal damping tank 57 and the vertical damping tank 58 include
Both contain a predetermined amount of viscous fluid 55. The viscous fluid 55 is made of, for example, silicone oil. The internal bottom plate 43 is a disc-shaped plate, and a damping plate 6 is provided on the outer peripheral surface of the internal bottom plate 43.
4 is fixed. The damping plate 64 is provided with a through hole 65 of an appropriate size. Here, the load receiving plate 41 is a plate for supporting a table of a vibration isolating table and the like. Further, the support column 42 is a rod-shaped member with sufficient rigidity, and the inner bottom plate 43
is hanging. Furthermore, the rod-shaped members 45 are made of steel shafts, etc., and a total of three rod-shaped members 45 are inserted into the through holes of the top plate 44.
It is screwed so that the internal bottom plate 43 is suspended. The air chamber 50 surrounded by the external bottom plate 52 and the outer wall 51 is hermetically sealed above by a flexible sealing material 61. In the air spring device of the present invention having the above configuration, the flexible sealing material 61 achieves a sufficiently low natural frequency in the vertical direction. Moreover, since the rod-shaped member 45 supports the support column 42 via the internal bottom plate 43, the horizontal natural frequency of the load receiving plate 41 is thereby reduced. The low natural frequency in the vertical direction is due to the flexible encapsulant 6
It is adjusted by selecting the diameter and rigidity of 1. Further, the natural frequency in the horizontal direction is adjusted by selecting the length, thickness, etc. of the rod-shaped member 45. On the other hand, a horizontal damping tank 57 surrounded by an intermediate bottom plate 54 and an inner wall 53 is suspended in a vertical damping tank 58, as shown in the figure. Here, when the intermediate bottom plate 54 vibrates in the viscous fluid 55, the vibration direction is mainly vertical, so the vertical damping tank 58 applies an damping effect to the load receiving plate 41 in the vertical direction. Ru. In addition, the internal bottom plate 43 and the damping plate 64 are suspended in the horizontal damping tank 57.
The viscous fluid 55 provides a damping effect to vibrations in the horizontal direction. In this case, since the rod-shaped member 45 has extremely high rigidity in the vertical direction, the internal bottom plate 45 is placed inside the horizontal damping tank 57.
3 is mainly vibrated in the horizontal direction. In addition, since the lateral rigidity of the flexible sealing material 61, which is generally made of a bellows, diaphragm, etc., is more than 20 times higher than the rigidity of the rod-shaped member 45, this overall stiffness in the direction parallel to the horizontal direction is The natural frequency of the device substantially depends on that of the rod-shaped member 45. Therefore, the damping effect that the vertical damping tank 58 contributes to the horizontal vibration is about 1/20 of that of the horizontal damping tank 57, and can be ignored. As a result of the above, in the device according to the present invention, the horizontal damping tank 57 and the vertical damping tank 58
However, they substantially independently contribute to damping in the horizontal and vertical directions, and do not interfere with each other. Therefore, for example, if it is desired to double or decrease only the damping effects in the vertical and horizontal directions, the adjustment can be easily carried out individually. The present invention is not limited to the above embodiments. In the above embodiment, the rod-shaped member 45 is arranged inside the diameter of the top plate 44 supported by the flexible sealing material 61 to achieve a small space. For example, the structure may be such that it is exposed outside the diameter of the top plate 44. Further, the internal bottom plate 43 and damping plate 64 provided in the horizontal damping tank 57 or the intermediate bottom plate 5 accommodated in the vertical damping tank 58
The shape of 4 may be changed in various ways depending on the required damping characteristics and the like. Further, the configuration may be modified so that the horizontal damping tank 57 is placed on the outside and the vertical damping tank 58 is placed on the inside. Note that although inert silicone oil is normally used as the viscous fluid 55, liquid rubber may also be used, for example. This liquid rubber is
Examples include inert polyisobutylene, liquid butyl rubber, and liquid polyisoprene. In particular, polyisobutylene has different viscosity depending on its molecular weight, and can be expected to have effects similar to those of silicone oil. In addition, in the embodiment shown in Fig. 1, all the components, including the horizontal spring element, the vertical damping element, and the horizontal damping element, can be housed within the vertical spring element, realizing a small space type. can do. By the way, when heavy and tall equipment is placed on the vibration isolation table, the system may not float stably and hunting may occur. This can be avoided by increasing damping in the vertical direction, but if the orifice is narrowed when adding damping, vibration isolation performance will also deteriorate. Since the present invention does not use orifice damping, the range in which the natural frequency changes when the damping effect is adjusted is narrow, and there is an advantage that vibration isolation performance can be maintained. That is, even if the damping is strengthened, the rate at which the natural frequency changes is small. In an air spring device like the one shown in Fig. 3, when the opening degree of the variable orifice valve (spicon) is changed, the first
As shown in the table, the natural frequency in the vertical direction changes.

【table】

[Table] On the other hand, when a viscous fluid is used, the change in its natural frequency is small as shown in FIG. Table 2 shows the difference between the undamped natural frequency ω _o and the damped natural frequency ω _d (viscous damping).

[Table] ω _o : Undamped natural frequency ξ: Damping constant ratio As described above, according to the device of the present invention, the rate of change in the natural frequency is very small, so deterioration of vibration isolation performance can be prevented. can be easily done. (Effects of the Invention) The air spring device of the present invention configured as described above elastically supports the load receiving plate movably in the vertical direction by the flexible sealing material and the air chamber, and has low natural vibration in the vertical direction. On the one hand, it is possible to reduce the natural frequency in the horizontal direction by elastically supporting the structure so as to be movable in the horizontal direction by a vertically erected rod-like member. Moreover, since the vertical damping tank and the horizontal damping tank are provided, damping effects can be applied to vibrations in each direction separately and independently, which has the advantage of increasing the degree of freedom in design.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the air spring device of the present invention, and FIGS. 2, 3, 7, 10, and 11 are separate examples of conventional air spring devices. FIG. 4 is a graph showing the relationship between vibration frequency and vibration transmissibility of the floor surface on which the air spring device is placed, and FIG. 5 is a graph showing the relationship between the vibration frequency and vibration transmissibility of the floor surface on which the air spring device is placed. FIG. 6 is a graph showing the relationship between vibration frequency and vibration acceleration, and FIG. 6 is a graph showing changes in vibration acceleration for air spring devices with various characteristics.
FIG. 8 is a graph showing the relationship between the vibration frequency of the floor surface and the vibration transmissibility using the damping constant ratio as a parameter, and FIG. 9 is an explanatory diagram showing the vibration damping effect when the damping constant ratio is changed. 41...Load receiving plate, 42...Support column, 43...
Internal bottom plate, 44... Top plate, 45... Rod-shaped member, 5
0... Air chamber, 55... Viscous fluid, 57... Horizontal damping tank, 58... Vertical damping tank.

Claims (1)

[Claims] 1 A load receiving plate 41 on which an object to be supported is placed; a flexible sealing material 61 is provided below the load receiving plate 41 to support the load receiving plate 41; and the load receiving plate 41 is movable primarily in the vertical direction. An air chamber 50 that elastically supports
and is erected substantially perpendicularly to the load receiving plate 41 to directly or indirectly support the load receiving plate 41, and elastically supports the load receiving plate 41 so as to be movable mainly in the horizontal direction. A rod-shaped member 45,
A horizontal damping tank 57 that accommodates the viscous fluid 55 and receives a part of the member connected to the load receiving plate 41 to suppress and damp horizontal vibration thereof.
and a vertical damping tank 58 that accommodates a viscous fluid, receives a part of the member connected to the load receiving plate, and suppresses and damps vibrations in the vertical direction. .