JPS6113115B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust system using a turbo-molecular pump in an electron microscope or the like.

In order to reduce contamination of samples in electron microscopes and the like, it is necessary to keep the inside of the microscope body clean (oil-free). For this purpose, instead of the conventionally commonly used oil diffusion pump,
Turbo molecular pump (hereinafter simply referred to as molecular pump)
It is possible to use

However, since such molecular pumps in principle require a high-speed rotation mechanism, there is a risk that the resolution of the electron microscope will decrease due to the vibrations generated by the rotation mechanism, and sufficient countermeasures against vibrations are required. Become. For this purpose, it is conceivable to firmly fix the molecular pump to the floor. This method has the advantage of being able to install the molecular pump directly under the mirror, but it requires foundation work and is very difficult to handle as it requires foundation work every time the mirror is installed. This has the disadvantage of being troublesome and increasing costs. In order to prevent this drawback, it is possible to install the molecular pump at a position quite far from the mirror, but this inevitably requires the use of a long exhaust pipe, which increases the exhaust resistance and increases the exhaust time. It has some drawbacks.

By the way, recently, in order to solve this problem, the vibration of the molecular pump is damped by the bellows by supporting the molecular pump by suspending it from the main exhaust pipe fixed to the frame. A device has been proposed. in this case,
When the mirror body is evacuated (vacuumed), the molecular pump is pulled upward by back pressure and the bellows is compressed.
The result is essentially the same as fixing the molecular pump directly to the exhaust pipe, and the vibrations of the molecular pump may be transmitted to the mirror body.

Therefore, it is an object of the present invention to prevent the bellows from being compressed by such back pressure of the pump, thereby preventing the vibrations of the molecular pump from being transmitted to the mirror body.

In order to achieve the above object, the present invention includes a mirror body,
An exhaust pipe connected to the mirror body, a mount placed on the floor via a vibration isolator to hold the mirror body and the exhaust pipe, and exhaust the mirror body through the exhaust pipe and bellows. equipped with a molecular pump for
The molecular pump is substantially suspended from the pedestal by the bellows, making it non-contact with the floor side, and in order to cancel the compressive force applied to the bellows by creating a vacuum inside the mirror body, The present invention is characterized in that a sealed air spring is provided between the pedestal side and the molecular pump side.

The present invention will be explained in detail below based on the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention, and 1 is a mirror body of a transmission electron microscope. The mirror body 1 is attached to a pedestal 2. The pedestal 2 is placed on a floor 5 by four pillars 4a to 4d (4c and 4d are not shown) each having a vibration isolating device 3. A main exhaust pipe 6 is placed behind the mirror body 1 and communicates with each chamber of the mirror body through sub exhaust pipes 7a, 7b, and 7c, and the main exhaust pipe 6 is connected to the mount 2.
The lower end 6a of the main exhaust pipe protrudes from the lower surface of the pedestal 2. Reference numeral 8 denotes a molecular pump, and the suction port 9 side of the molecular pump is connected to the lower end 6a of the main exhaust pipe 6 via a bellows 10 made of stainless steel, for example. In this case, the lower end of the molecular pump 8 is suspended from the floor 5, that is, the molecular pump is suspended from the main exhaust pipe 6 via the bellows 10. Further, the discharge port 11 of the molecular pump 8 is connected to an oil rotary pump via a pipe (not shown).

12a, 12b, and 12c (12c is not shown) are cylinders fixed to the main exhaust pipe 6 (or the mount 2) via a mounting plate 13, and these cylinders are arranged equidistantly around the main exhaust pipe 6. They are arranged at intervals and parallel to the main exhaust pipe 6, and within each cylinder there are movable rods 14a, 14b, 14.
Pistons 15a, 15b, 15c (1
4c, 15b and 15c (not shown) are slidably inserted. Each of the moving rods 14a passes through each cylinder side wall, and a push plate 15 is attached to the tip thereof. The push plate 15 is formed into an annular shape and is placed on the outer periphery of the bellows 10, and a receiving plate 16 is placed below the push plate to face it. The receiving plate 16 is connected to the bellows 10.
It is fixed to the flange 17a portion of. Furthermore, the internal pressure between the push plate 15 and the receiving plate 16 is, for example, 1.
An annular sealed air spring 18 maintained at kg/cm ² is interposed.

Pipes 19a and 19b are connected to an upper chamber 20a and a lower chamber 20b, respectively, which are partitioned by a piston 15a in the cylinder 12a, and the other ends of both pipes are connected to a compressor 22 via a switching valve 21. There is. Therefore, by arbitrarily switching the switching valve 21, compressed air can be introduced into the upper chamber 20a or the lower chamber 20b within the cylinder 12a. 23 is a pressure regulating valve attached to the pipe 19a. Although not shown, the other two cylinders 12b are also provided with pipes connected to the compressor 22 in the same way as 12a.

In such a device, three cylinders 12a
By introducing a predetermined pressure of compressed air from the compressor 22 into the upper chamber 20a side and pressing the push plate 15 downward, the back pressure exerted on the molecular pump 8 due to the exhaust of the interior of the mirror body 1 can be reduced. Therefore, the bellows 10 can be used in a substantially free length state without being compressed.

Here, 24 and 25 in the figure move downward due to the pressing force of the push plate 15 when the inside of the mirror body 1 leaks and the back pressure to the molecular pump 8 is released, and the bellows 1
One wire 24 is bent into a U-shape and fixed to the flange 17a of the bellows, and the other wire 25 is passed through one wire 24 and attached to the bellows. It is fixed to the flange 17b portion of. When the back pressure applied to the molecular pump 8 and the pressing force of the push plate 15 are balanced, the two wires are separated from each other as shown in the figure, and when the back pressure applied to the molecular pump disappears, both wires are latched. It is structured as follows.

As described above, the present invention has a structure in which the back pressure applied to the molecular pump via the annular closed air spring is canceled out, so that the bellows is not compressed by the back pressure applied to the molecular pump and is in a substantially free length state. It can be used in As a result, the vibration of the molecular pump can be attenuated by the bellows or sealed air spring, thereby preventing a decrease in resolution. Further, as shown in FIG. 2, the damping effect is increased by providing a large number of protrusions 26 and 27 on the whole or part of the contact surface of the sealed air spring 18 with the push plate 15 and the receiving plate 16. , it can have an even stronger damping effect, and has a great practical effect.

In the above-described embodiment, an air cylinder mechanism was used as a means for generating a pressing force to cancel the back pressure applied to the molecular pump, but other known means such as a screw mechanism may also be used.

Furthermore, although the case where the method is applied to a transmission electron microscope has been described, it can be similarly applied to a scanning electron microscope or the like.

[Brief explanation of the drawing]

FIG. 1 is a schematic structural diagram showing one embodiment of the present invention, and FIG. 2 is a sectional view showing another embodiment of the present invention. 1: Mirror body, 2: Frame, 3: Vibration isolator, 4a and 4b: Support column, 5: Floor, 6: Main exhaust pipe, 8: Molecular pump, 10: Bellows, 12a and 12b: Cylinder, 13: Mounting plate , 14a and 14b: moving rod, 15: push plate, 16: receiving plate, 17a and 17
b: flange, 18: sealed air spring, 19a and 19b: pipe, 21: switching valve, 22: compressor, 24 and 25: wire.

Claims (1)

[Claims] 1. A mirror body, an exhaust pipe connected to the mirror body, a pedestal mounted on the floor via a vibration isolator to hold these mirror bodies and the exhaust pipe, and and a molecular pump for evacuating the mirror body, the molecular pump being substantially suspended from the pedestal by the bellows so as not to contact the floor side, and creating a vacuum inside the mirror body. An exhaust system for an electron microscope or the like, characterized in that a sealed air spring is provided between the mount side and the molecular pump side in order to cancel the compressive force applied to the bellows.