JPS6318794Y2 - - Google Patents

Description

[Detailed Description of the Invention] <<Industrial Application Field>> This invention relates to a magnetically levitated rotating shaft support device used for example in a turbo-molecular pump, and in particular,
This invention relates to an improvement in mounting a sensor for detecting the levitation state.

<Prior Art> One of the structures of a turbomolecular pump is a cylindrical housing 1 with an open top and a bottom, as shown in Fig. 1.
A rotor case 2 is installed inside the rotor case 2, rotor blades 4 having multistage blades are attached to a rotor shaft 3 protruding from the upper part of the rotor case 2, and a stator is fixed to the inner periphery of the housing 1 between each blade. Some are equipped with wings 5.

A high frequency motor 6 is disposed within the rotor case 2 to rotate the rotor shaft 3 at high speed.

When rotating the rotor blades 4 at such high speeds, supporting the rotor shaft with ordinary bearings is undesirable due to wear and tear, and lubricating oil from the bearings evaporates. The rotor shaft 3 is supported by a magnetic support method.

In other words, in order to deal with the horizontal vibration of the rotor shaft 3, a radial electromagnet 7 is arranged at the periphery of the rotor shaft 3, and a sensor 8 is arranged to detect this vibration. By controlling the attractive force of each electromagnet 7, the axial center of the rotor shaft 3 is kept constant.

Further, to support the rotor shaft 3 in the axial direction, a shaft end case 9 is fixed to the bottom opening of the rotor case 2 at the lower end of the rotor shaft 3, and a separation distance from the shaft end of the rotor shaft 3 is set at the center of the inner bottom surface of the shaft end case 9. A sensor 10 for detection is arranged, and a ring-shaped permanent magnet 11 is embedded in the inner bottom surface of the shaft end case a around the sensor 10, while a permanent magnet 11 of different polarity is embedded in the lower part of the rotor shaft 3. The rotor shaft 3 is always pulled downward by the attractive force of the permanent magnets 11, and the electromagnet 13 is installed around the rotor shaft 3 in the upper part of the shaft end case 9. Furthermore, a yoke 14 is fixed to the rotor shaft 3 facing the electromagnet 13.

By energizing the electromagnet 13 to produce an attractive force corresponding to the detection output of the sensor 10, the rotor shaft 3 is supported in a floating state against the attractive force of the permanent magnet 11.

Note that reference numerals 15 and 16 in the figure are dry bearings for protection, and when the rotor shaft 3 loses its buoyancy force when stopped, its own weight and the attractive force of the permanent magnet 11 cause the dry bearings 15 and 16 to
The structure is such that it is supported by a bearing.

In the rotor shaft support device configured as described above, the shaft end cover 9 is integrally formed by turning or the like, and therefore, the distance between the lower end of the rotor shaft 3 and the sensor 10 depends on the machining accuracy, and the initial setting is due to assembly accuracy.

However, the sensor 10 uses a magnetic coil, and therefore, the sensitivity of the sensor 10 to the sensor target 3a becomes non-linear depending on the interval.

Therefore, if the distance between the sensor target 3a and the sensor 10 increases significantly within the range of processing and assembly tolerances, conventional methods have been used to compensate for the low sensor sensitivity by increasing the circuit gain. I have to. However, sensor 10
Since the sensitivity of the circuit is nonlinear, increasing the circuit gain tends to cause oscillation, making adjustment difficult.

<<Purpose of the invention>> The object of this invention is to enable the initial adjustment of the sensor gain to be easily performed in the magnetically levitated rotating shaft support device as described above.

<<Structure of the invention>> In order to achieve the above object, the present invention includes a case on the shaft end side that is attached to a sleeve that surrounds the outer periphery of the rotating shaft, and that is screwed onto the sleeve.
The rotating shaft is characterized in that it is divided into two parts, including a cover that covers the shaft end, and the distance between the sensor and the shaft end can be adjusted according to the screwing amount of the shaft end cover.

<<Example>> Fig. 2 shows the main parts of a case where this invention is applied to a turbo molecular pump.

It should be noted that other parts than the main parts are completely the same as those shown in FIG. 1, so a description thereof will be omitted, and the same parts as in the prior art will be described using the same reference numerals.

In the figure, the shaft end case consists of a sleeve fitted into the bottom opening of the rotor case 2, and a shaft end cover 21 fitted into the inner circumference of the sleeve.

A female threaded portion 22 is cut on the inner periphery of the sleeve 20, and a male threaded portion 23 is cut on the outer periphery of the shaft end cover 21 opposite to this.
The distance between the sensor 10 and the sensor target 3a can be adjusted according to the pitch of the threaded portion by adjusting the amount by which the cover 21 is screwed in relative to 0.

<<Effect of the invention>> Since this invention is constructed as described above, when this invention is applied to a support device for the rotor shaft of a turbo molecular pump, for example, after assembling the rotor shaft 3 and each part in the rotor case, Even the sensitivity of the sensor can be easily adjusted to be located in the linear region. Therefore, in the present invention, gain adjustment is performed in a linear region, compared to conventional circuits in which adjustment is performed only, so that adjustment is easy and there are no phenomena such as oscillation.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the structure of a turbomolecular pump having a magnetically levitated rotary shaft support device, and FIG. 2 is a partially enlarged sectional view showing the main parts of this invention. 3... Rotor shaft, 10... Sensor, 11... Permanent magnet, 13... Electromagnet, 20... Sleeve, 2
1... Shaft end cover, 22... Female threaded part, 23...
Male thread part.

Claims (1)

[Scope of utility model registration request] A sensor is installed on the inner bottom surface of the case that covers the lower end of the rotating shaft to detect the distance from the shaft end.
A permanent magnet that attracts the rotating shaft is placed around the sensor, and an electromagnet that attracts the rotating shaft is placed on the case so as to face the rotating shaft in a direction opposite to the attracting direction of the permanent magnet. A rotating shaft support device that supports a rotating shaft in a floating state by exciting an electromagnet to generate an attractive force, the case including a sleeve surrounding the outer periphery of the rotating shaft;
The rotary shaft support is divided into two parts, including a shaft end cover that is screwed into the sleeve, and the distance between the sensor and the shaft end can be adjusted according to the screwing amount of the shaft end cover. Device.