JP2012032004A - Vibration isolation mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration isolation mechanism, capable of enhancing the vibration isolation performance without increasing the height of a device.SOLUTION: The vibration isolation mechanism is required upon using a precision device accompanied by vibration caused by a turbo pump or the like. The mechanism uses a bellows for vacuum sealing in which two or more dampers are arranged in series. The mechanism is configured to include: a configuration of concentrically disposing the bellows; and a configuration of disposing one of a rubber member supporting force by vacuum pressure, outside the object of vibration isolation.

Description

  The present invention relates to a vibration isolation mechanism, and more particularly to a vibration isolation mechanism suitable for use in an electron microscope or the like.

  A vacuum pump such as an oil diffusion pump (DP) or a turbo molecular pump (TMP) is used for an apparatus that requires high vacuum such as an electron microscope or a charged particle beam drawing apparatus. In recent years, oil used in DP has been released as vapor in vacuum, and contamination of inspection objects and processing objects has become a problem, and TMP has been adopted to obtain a clean vacuum. Has increased.

  Since TMP performs evacuation by rotating a wing at high speed, it generates vibration proportional to the number of rotations. On the other hand, since the above-described apparatus is used for observation and processing of a fine structure, an accurate image cannot be obtained by vibration. Therefore, it is usual to arrange a vibration isolator between the TMP and the device to suppress vibration transmission generated from the TMP.

  FIG. 8 is a diagram showing a configuration example using a conventional one-stage damper (vibrator). In the figure, 1 is a device side flange, 2 is a pair of flanges, and 3 is a bellows. 4 is a rubber disposed outside the bellows 3. The pair of flanges 2, bellows 3, and rubber 4 constitute a vibration isolator (damper). The bellows 3 is welded to the flange 2. This vibration isolator is fixed to the apparatus side flange 1 by a clamp 5. Reference numeral 6 denotes a TMP provided at the lower stage of the vibration isolator. The TMP 6 is fixed to the vibration isolator by a clamp 5.

  The vacuum is sealed by the bellows 3 and the O-ring 7. This vacuum pressure causes the bellows 3 to be shrunk upward in the figure, but the rubber 4 is compressed and generates a force against it. FIG. 9 is a diagram showing a dynamic model of the vibration isolation mechanism shown in FIG. The same components as those in FIG. 8 are denoted by the same reference numerals. Here, only the one-degree-of-freedom vibration system in the vertical direction in the figure is considered. In this model, a mass a (mass M1) composed of a TMP 6, a flange 2 and a clamp 5 is formed by a spring b (spring constant k1) composed of a bellows 3 and rubber 4 and mainly rubber 4 with respect to the apparatus side flange 1. It can be regarded as a lumped parameter system connected via the attenuation term c.

At this time, the vertical vibration transfer function from the mass a to the apparatus side flange 1 is shown in FIG. FIG. 10 is a diagram showing transfer function characteristics of the vibration isolation mechanism shown in FIG. The horizontal axis represents the logarithm frequency [Hz], and the vertical axis represents the transmission rate [dB]. The transmissibility shows 0 [dB] in the low frequency range, has a resonance peak at the break frequency f1 [Hz], and then decreases at −40 dB / decade. Here, the break frequency f1 is f1 = (1 / 2π) √ (k1 / M1)
It is represented by FT shown in FIG. 10 is the rotational speed of TMP, and indicates that vibration transmission is suppressed by G0 [dB] by the vibration isolator at this frequency.

  However, this may not be sufficient to suppress vibration transmission. In this case, as shown in FIG. 11, the vibration isolator may be connected in series in two stages. FIG. 11 is a diagram showing a configuration example using a conventional two-stage damper (vibrator). The same components as those in FIG. 8 are denoted by the same reference numerals. FIG. 12 is a diagram showing a dynamic model of the vibration isolation mechanism shown in FIG. The same components as those in FIG. 9 are denoted by the same reference numerals. The mass d (mass M2) corresponds to the mass including the two flanges 2 of the vibration isolator connection portion in series and the clamp 5.

  A spring b and a damping term c are connected to the upper and lower sides, respectively. The transfer function at this time is as shown in FIG. In FIG. 13, the first break frequency f1 'shifts to a frequency lower than f1 [Hz] in FIG. 10 because two springs b (see FIG. 12) are connected in series. Since the natural vibration in the vertical direction of the mass d occurs at f2 [Hz], a resonance peak due to this is seen, and the transfer function becomes smaller at −80 [dB / decade] at a frequency equal to or higher than f2. By making this second break frequency f2 [Hz] lower than fT [Hz], the transmission rate at fT [Hz] can be made lower as shown in the figure. At this time, the vibration transmission is suppressed by G1 [dB] by the vibration isolator. As a result, G1> G0 with respect to the suppression value G0 of FIG. 10, and the suppression value is larger when the two-stage damper is used than with the one-stage damper, and it is difficult to transmit vibration to the apparatus side. I understand.

  This type of conventional device is a vibration isolation device including a vibration isolation mechanism that supports a vibration isolation object in a vacuum atmosphere, and the vibration isolation mechanism includes a plurality of metal bellows with a coupling member therebetween. A bellows assembly that is connected to communicate with each other in the vertical direction and has compressed gas enclosed therein, and one end is attached to a side surface of the coupling member, and the coupling member is connected to the axial direction of the bellows assembly. A vibration isolator including a spring member elastically supported in an intersecting direction is known (see, for example, Patent Document 1).

  Further, in the vibration isolation device including the vibration isolation mechanism 9 below the top plate that supports the vibration isolation object, the vibration isolation mechanism communicates a coupling member having an arbitrary mass between the upper metal bellows and the lower metal bellows. There has been known a vibration isolator including a bellows combination that is connected in series with each other (see, for example, Patent Document 2).

JP 2007-205543 A (paragraphs 0012 to 0021, FIGS. 1 to 4) JP 2006-220204 A (paragraphs 0017 to 0031, FIGS. 1 and 2)

  As described above, when the vibration isolator has two stages, the vibration isolation characteristics are improved as compared with the case of one stage. However, if the vibration isolator is connected in series as shown in FIG. 11, the height of the vibration isolator is doubled or more. Depending on the device, there may be a case where the clearance from the floor cannot be made large. In this case, a two-stage configuration cannot be taken, and there is a problem that the vibration isolation performance is lowered.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a vibration isolation mechanism capable of improving vibration isolation performance without increasing the height of the apparatus.

  The invention described in claim 1 is a vibration isolation mechanism that is required when using a precision device such as a turbo pump with vibration generation, and uses a two-stage or more damper in a series configuration. Is used, a dynamic vibration absorber is provided between the two bellows configured in series.

  According to the present invention, by providing a damper in the intermediate mass provided in the intermediate portion between the two bellows, it is possible to suppress the deterioration of the cutoff characteristic at the break frequency or to lower the resonance peak at the break frequency. , Vibration isolation characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the present invention. The same components as those in FIG. 8 are denoted by the same reference numerals. The feature of the present invention is that the bellows are arranged concentrically twice as shown in the figure. Reference numeral 13 denotes a bellows arranged outside, and 14 denotes a bellows arranged inside. FIG. 2 is a diagram showing details of the connecting portion of the bellows. The outer bellows 13 and the inner bellows 14 are connected by a flange 18.

  The outer bellows 13 has one end connected to the flange 17 and the other end connected to the flange 18. On the other hand, the inner bellows 14 has one end connected to the flange 18 and the other end connected to the flange 28. As is clear from the above description, it can be seen that the bellows 13 and the bellows 14 are connected in series. Reference numeral 1 denotes a device side flange. The flange 17, the bellows 13, the flange 18, the bellows 14, and the flange 28 are connected by welding. A rubber 15 that supports the vacuum pressure is disposed outside the bellows 13.

  A flange 29 is connected to the flange 28 by a bolt, and a rubber 16 is disposed between the flange 29 and the flange 18 so as to support a vacuum pressure applied to the bellows 14. The TMP 6 is fixed to the flange 28 with a clamp 30. A mass 27 is disposed outside the flange 18 via a viscoelastic material 19.

  The viscoelastic material 19 and the mass 27 form a damping mechanism for the vibration of the flange 18. According to this embodiment, since the rubber 16 is disposed outside the TMP 6, the whole can be shortened in the height direction. In this embodiment, the height direction is slightly extended (for example, 9 mm) as compared with the case where a single-stage vibration isolator is used. Therefore, since the clearance between the floor 8 and the apparatus-side flange 1 is small, it is possible to apply a two-stage vibration isolator even to an apparatus that can only use one-stage vibration isolator. The operation of the apparatus configured as described above will be described below.

  FIG. 3 is a diagram showing a dynamic model according to the first embodiment of the present invention. A mass d corresponding to the flange 18 is supported by the device side flange 1 by a bellows 13 and a spring e corresponding to the rubber 15 and a damping term f. The lower part (mass M3) of the mass d is connected to the mass a (mass M1) corresponding to the TMP 6 and the flanges 28 and 29 by the spring b corresponding to the bellows 14 and the rubber 16 and the damping term c. The mass d is connected to a spring g corresponding to the viscoelastic material 19 and a damping mechanism including a damping term h and a mass i.

  The transfer function in this dynamic model is shown in FIG. The first corner frequency f1 '' is a value smaller than the corner frequency f1 shown in FIG. Note that the corner frequency f1 ′ and the corner frequency f ″ shown in FIG. 7 do not necessarily match. Here, the mass M3 of the mass d is made larger than the mass b of FIG. 12 (M2 <M3), and the upper and lower spring constants k1 ′ and k2 are set to the same level as in FIG. The point frequency f2 ′ can be made lower than f2 in FIG. As a result, the transmission rate at fT is lower, and vibration transmission at the TMP rotational speed can be further suppressed. That is, the attenuation amount at fT in FIG. 4 is G2, and G2> G1.

  Next, with respect to the resonance peak occurring at f2 ′, the damping mechanism by M4, k3, and c3 in FIG. 3 is adjusted so as to suppress the natural vibration (f2 ′ [Hz]) of M3, and the transfer function The peak can be reduced. Accordingly, it is possible to suppress the deterioration of the transmission rate due to the resonance of f2 ′ [Hz].

  As described above, the vibration isolation mechanism having a good transfer function can be realized by moving the second break frequency to the lower frequency side and suppressing the resonance magnification at this frequency.

  FIG. 5 is a block diagram showing a second embodiment of the present invention. This embodiment differs from the embodiment shown in FIG. 1 in that the dampers are not arranged concentrically but are connected in series in the vertical direction, and between the first-stage vibration isolator and the second-stage vibration isolator. A damper is provided. In the figure, 40 is a first-stage vibration isolator, and 41 is a second-stage vibration isolator. Reference numeral 42 denotes a damper attached between the first-stage vibration isolator 40 and the second-stage vibration isolator 41. In the damper 42, 53 is a mass, 54 is a viscoelastic material, and 55 is a flange. The first-stage vibration isolator 40 and the second-stage vibration isolator 41 are coupled by a damper 42.

  The operation of the embodiment thus configured will be described. FIG. 6 is a diagram showing a dynamic model according to the second embodiment of the present invention. a is a mass (mass M1), b is a spring, and c is a damping term. d is a mass (mass M3), and the constant of the spring and the damping term connected between the mass d and the apparatus side flange 1 is the same as the constant of the spring and the damping term connected between the mass a and the mass d. . The mass (mass M4) i connected to the mass d, the spring g, and the damping term h constitute a dynamic vibration absorber, and this portion corresponds to the dynamic model of the damper 42 in FIG.

  FIG. 7 is a diagram showing the transfer function characteristics of the second embodiment of the present invention. The first corner frequency f1 ′ moves to the lower frequency side than the corner frequency f1 shown in FIG. 10, and the second corner frequency f2 ′ is also lower than the corner frequency f2 shown in FIG. Has moved. As a result, the attenuation G2 at the TMP rotation frequency fT becomes a sufficiently large value, and the vibration of the TMP can be prevented from being transmitted to the apparatus side flange 1.

  According to this embodiment, by providing the damper in the intermediate mass provided in the intermediate portion between the two bellows, the break frequency can be lowered, and the vibration cutoff characteristic can be improved.

  In the above-described embodiment, the vibration in the vertical direction has been discussed. However, the vibration in the horizontal direction can be considered in the same manner. In this case, the transfer function is determined not by the spring and the damping term in the compression direction but by the spring and the damping term in the horizontal shear direction. In this case as well, the horizontal vibration mode of the intermediate mass sandwiched between the bellows determines the second break frequency. Increasing this mass has the effect of lowering the second break frequency as in the case of the vertical direction.

  Further, the viscoelastic material 19 (see FIG. 1) and the mass 27 can suppress the vibration absorption peak of this frequency even with respect to horizontal vibration, and similarly prevent deterioration of the transfer function due to resonance. it can. Therefore, the characteristic of the vibration transfer function in the horizontal direction is good as in the vertical direction.

As described above in detail, the present invention has the following effects.
1) By arranging double bellows concentrically and making effective use of the space outside the TMP, a two-stage vibration isolator can be used at almost the same height as that of the first stage. Higher vibration isolation performance can be provided even for a device that does not take up much space.
2) By increasing the intermediate mass between the bellows, the second break frequency of the transfer function can be lowered, and the vibration isolation performance in the high frequency region including the TMP rotation frequency can be improved.
3) By providing the intermediate mass with a damping function, it is possible to prevent deterioration of the transmission rate due to resonance at the break frequency.

  Thus, according to the present invention, it is possible to provide a vibration isolation mechanism that has a good transfer function and is space-saving in the height direction.

It is a block diagram which shows the 1st Embodiment of this invention. It is a figure which shows the detail of the connection part of a bellows. It is a figure which shows the dynamic model of the 1st Embodiment of this invention. It is a figure which shows the transfer function characteristic of the 1st Embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of this invention. It is a figure which shows the dynamic model of the 2nd Embodiment of this invention. It is a figure which shows the transfer function characteristic of the 2nd Embodiment of this invention. It is a figure which shows the structural example using the conventional 1 step | paragraph damper. FIG. 9 is a diagram illustrating a dynamic model of the vibration isolation mechanism illustrated in FIG. 8. It is a figure which shows the transfer function characteristic of the vibration isolation mechanism shown in FIG. It is a figure which shows the structural example using the conventional 2 step | paragraph damper. It is a figure which shows the dynamic model of the vibration isolation mechanism shown in FIG. It is a figure which shows the transfer function characteristic of the vibration isolation mechanism shown in FIG.

1 Equipment side flange 6 TMP (turbo molecular pump)
7 O-ring 13 Bellows 14 Bellows 15 Rubber 16 Rubber 17 Flange 18 Flange 19 Viscoelastic material 27 Mass 28 Flange 29 Flange 30 Clamp

Claims (1)

In a precision device, a vibration isolation mechanism required when using a device with vibration generation such as a turbo pump, which uses a vacuum seal bellows that uses a two-stage damper in a series configuration,
A vibration isolator provided with a dynamic vibration absorber between the two bellows configured in series.

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