JPH018714Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an opening/closing control device for a leak valve of a turbo-molecular pump that evacuates an evacuated chamber in a vacuum device such as an electron microscope.

[Prior Art] In order to obtain useful results with an analytical electron microscope incorporating a non-dispersive X-ray spectrometer, an electron energy analyzer, etc., it is necessary to reduce sample contamination as much as possible. Therefore, a high vacuum and a highly clean vacuum are required inside the mirror body, and an oil-free turbo molecular pump is used as the vacuum pump.

[Problems to be solved by the invention] By the way, even when the pump power is turned off, the turbo molecular pump does not immediately stop rotating, but continues to rotate at high speed for several minutes or more.

In such turbomolecular pumps, when air is introduced (leaked) into the pump with the rotor blades stopped when the pump is stopped, the oil used in the pump bearings will leak into the high vacuum side of the pump. This causes the inconvenience of backflow.

Therefore, conventionally, the leak valve is opened at the same time as the turbo molecular pump is turned off. As a result, air is introduced while the rotor blades are rotating at high speed, which applies a large impact to the rotor blades, causing damage to the rotor blades and bearings, and shortening the lifespan of the turbomolecular pump. There is a risk of it being shortened.

Therefore, in the past, a method has been used to gradually leak the inside of the pump by making the exhaust conductance very small, such as by making the hole diameter of the leak valve very small or by narrowing the piping of the leak valve. If the change in pressure at this time is represented in a graph, it will be as shown in FIG. 4a. In the same figure, P ₀
is the pressure when the pump is turned off, Pa is the atmospheric pressure,
The rate of pressure increase (inclination) θ is determined by the exhaust conductance of the leak valve, and is set as large as possible within an allowable range.

However, this method has the disadvantage that clogging is likely to occur, and handling is very troublesome, such as disassembling and cleaning each time, and it takes a long time to prevent leaks.

In other words, in reality, once the leak has sufficiently progressed to reach a pressure P ₁ at which there is no longer any risk of damage, it is possible to rapidly introduce atmospheric air, as shown in Figure 4b, for example. Compared to Figure 4a, the time required for leakage can be reduced by _T0 . Focusing on this point, we installed two leak valves with different pore diameters, and the first leak valve with the smaller pore diameter allows leakage to occur for a certain period of time, that is, until the impact of gas molecules does not have an adverse effect, and then the first leak valve with the larger pore diameter Second
One possible method is to use a leak valve to cause a sudden leak.

However, this method does not solve the problem of clogging of the first leak valve, which has a small hole diameter, as described above, and has the disadvantage that another leak valve must be added.

In view of these points, the present invention does not cause clogging,
Moreover, the purpose is to shorten the leak time as much as possible without providing a new leak valve.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an evacuated chamber, a turbo molecular pump for evacuating the evacuated chamber,
It is characterized by comprising a leak valve for leaking the inside of the turbo-molecular pump, and configured to open and close the leak valve intermittently when leaking inside the turbo-molecular pump.

[Embodiment] FIG. 1 is a schematic diagram showing an embodiment of the present invention, and numeral 1 indicates an evacuated chamber of an electron microscope or the like. Reference numeral 2 denotes a turbo molecular pump for evacuating the inside of the chamber 1 to be evacuated via an exhaust pipe 3, and the back pressure side of this turbo molecular pump is evacuated via an exhaust pipe 4 by an oil rotary pump 5. 6 is a power source for the turbo molecular pump 2. A leak valve 7 is a solenoid valve connected to the exhaust chamber 1, and is opened and closed by a drive circuit 8. 9 is a second
This is a pulse generation circuit for supplying drive pulses as shown in FIG. C, and a stop signal is supplied from the power supply 6 to this pulse generation circuit. 10
is a vacuum gauge for measuring the pressure inside the evacuated chamber 1 (turbo molecular pump 2).

In the above configuration, the leak valve 7 used has a large hole diameter and has an exhaust conductance comparable to that of the second leak valve that performs rapid leakage after _P1 in FIG. 4b.

Therefore, while the turbo molecular pump 2 is evacuating the evacuated chamber 1, the time as shown in FIG.
At _t0 , the pump power supply 6 is turned off to stop supplying electricity to the turbomolecular pump, and at the same time, the pump power supply 6 generates a stop signal shown in FIG. 2b and supplies it to the pulse generation circuit 9. The pulse generating circuit 9 emits the valve opening/closing signal shown in FIG. 2C based on the stop signal,
The signal is sent to the drive circuit 8. This valve opening/closing signal causes the leak valve to be opened during period T1 and closed during period T2, so that it is intermittently opened and closed four times, and then continuously opened. If the change in pressure at this time is expressed graphically, it will be as shown by the solid line A in Figure 4c.The pressure can be increased within an allowable range while using a leak valve with a large hole diameter, and the pressure P ₁ After reaching , the leak can proceed rapidly, so the leak time can be shortened without adding a leak valve. Moreover, since the hole diameter is large, there will be no clogging of the leak valve.

Note that the inside of the turbo molecular pump 2 should not be completely brought to atmospheric pressure, but at a certain pressure (for example, about 200 Torr).
When the desired pressure is reached by the vacuum gauge 10, the leak valve 7 may be closed manually or automatically as shown by the dotted line in FIG. 2C.
Furthermore, since θ and P ₁ differ depending on the volumes of the evacuated chamber 1 and the turbomolecular pump 2, it is necessary to determine T ₁ and T ₂ accordingly.

FIG. 3 is a schematic diagram showing another embodiment of the present invention, in which the same numbers as in FIG. 1 indicate the same components. In the figure, 11 is a control circuit to which a stop signal is supplied from the pump power supply 6 and a signal corresponding to the pressure measured by the vacuum gauge 10 is supplied.

In this embodiment, the function Fo that specifies the timing to open the leak valve and the function Fs that specifies the timing to close the leak valve as shown in FIG. 5a are determined in advance based on the change curve in FIG. 4b. The functions Fo and Fs are stored in the control circuit 11 in advance.

Therefore, in synchronization with turning off the pump power supply 6, the second
When the stop signal shown in FIG.
When intersects with the function Fs, the leak valve 7 is closed and the function Fo
When the leak valve 7 intersects with the leak valve 7, control is performed to open the leak valve 7.
Therefore, the leak valve 7 is opened and closed intermittently as shown in Fig. 5b, allowing the pressure to rise within an allowable range, and after the pressure exceeds _P1 , it is opened continuously, so that the leak valve 7 is opened and closed intermittently as shown in Fig. You can proceed with the leak.

Note that the inside of the turbo molecular pump 2 should not be completely brought to atmospheric pressure, but at a certain pressure (for example, about 00 Torr).
When the desired pressure is reached by the vacuum gauge, the leak valve 7 may be closed manually or automatically as shown by the dotted line in FIG. 5B.

In this embodiment, since the opening and closing of the leak valve is controlled while monitoring the pressure, even if the exhaust conductance of the leak valve changes, there will be no problem such as sudden leakage outside the allowable range.

In the above description, a leak valve attached to the evacuated chamber was used to prevent leakage from the turbo-molecular pump, but it goes without saying that a leak valve or a vacuum gauge may be attached directly to the turbo-molecular pump. In this case, a valve is provided between the evacuated chamber 1 and the turbomolecular pump 2.

[Effects of the invention] As described above, in the present invention, leaks from the turbomolecular pump are detected by intermittently opening and closing the leak valve with a relatively large hole diameter, which eliminates the need for disassembly and cleaning due to clogging, and makes handling easier. In addition, it is highly practical, as it is not necessary to provide two leak valves with different hole diameters, and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a diagram for explaining its operation, FIG. 3 is a schematic diagram of the configuration showing another embodiment of the present invention, and FIGS. FIG. 4c is a graph showing changes in pressure within the turbomolecular pump, and FIGS. 5a and 5b are diagrams for explaining the operation of another embodiment of the present invention. 1...Evacuated chamber, 2...Turbo molecular pump,
3, 4...Exhaust pipe, 5...Oil rotary pump, 6...
Pump power supply, 7... Leak valve, 8... Drive circuit,
9... Pulse generation circuit, 10... Vacuum gauge, 11...
...control circuit.

Claims (1)

[Scope of utility model registration request] It is equipped with an evacuated chamber, a turbo-molecular pump for evacuating the evacuated chamber, and a leak valve for leaking the inside of the turbo-molecular pump. 1. An opening/closing control device for a leak valve for a turbo molecular pump, characterized in that it is configured to open and close automatically.