JPS6313918A - Attitude control device for rotating shaft of magnetic bearing type turbo-molecular pump - Google Patents

Abstract

PURPOSE:To certainly control and prevent vibration on the side of a stator by removing the frequency component of the number of revolutions from a detecting signal for the radial position of a rotating shaft used for controlling the attitude of the rotating shaft rotating in its magnetically floating state. CONSTITUTION:The position of a rotor 12 is detected by an axial position sensor 30 and radial position sensors 32, 34, and the number of revolutions is detected by a sensor 36 for the number of revolutions, and thereby one pulse signal is made to occur per revolution. Detecting signals from said radial position sensors 32, 34 are supplied to the one comparison input side of a comparator 40, and a signal corresponding to the reference position of a rotating shaft is supplied from a reference position setting device 42 to the other comparison input side of said comparator 40. Therefore, the rotor 12 is moved and controlled in the direction which makes its position detected by the sensor 32 coincide with its reference position. In addition to that, since a band elimination filter 20 removes the frequency component of the number of revolutions from a signal issued by said sensor 32, vibration on the side of a stator 16 can be prevented even when the rotor 12 fluctuates in the number of revolutions.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a device for controlling the attitude of a magnetically levitated rotating shaft in a magnetic bearing type turbomolecular pump.

(Background of the Invention) In a magnetic bearing type turbomolecular pump, attitude control of a rotating shaft that rotates while being magnetically levitated is performed by moving the shaft in a direction in which the detected position in the radial direction coincides with the target position. .

However, the inertial axis and the central axis of the rotating shaft do not exactly coincide with each other, and therefore the radial position detection signal of the rotating shaft includes an imaging component of the same frequency that corresponds to the rotational speed.

Therefore, when the rotational axis is controlled to move from the inertial axis toward the central axis l\ by using the detection signal as a feedback signal, imaging occurs on the stator side at the same frequency as the above-mentioned imaging component.

Therefore, in an electron microscope using this type of pump, the measurement results are adversely affected. Therefore, in the past, the vibration component was removed from the radial direction detection signal of the rotating shaft using a notch filter whose center frequency was equal to the steady rotational speed of the rotating shaft.

However, since the center frequency of the notch filter is fixed, a conventional problem has arisen in that vibrations corresponding to the rotational speed of the rotating shaft occur on the stator side when the pump starts and stops and when the shaft load changes.

(Object of the invention) The present invention has been made in view of the above-mentioned conventional problems, and
The purpose is to provide this type of rotary shaft attitude control device that can sufficiently suppress and prevent imaging of the stator side regardless of the rotational speed of the magnetically levitated rotary shaft.

(Structure of the Invention) In order to achieve the above object, the present invention includes: a shaft radial position detection means for detecting the radial position of a magnetically levitated rotating shaft; a shaft movement control means for moving; a shaft rotation speed detection means for detecting the rotation speed of the rotating shaft; a shaft rotation speed component removal means for removing a component corresponding to the detected rotation speed from an amount corresponding to the detected position of the shaft movement control means; It is characterized by having the following.

(Description of Embodiments) Hereinafter, preferred embodiments of the apparatus according to the present invention will be described based on the drawings.

Figure 1 shows the internal structure of the outer rotor type magnetic bearing type Woobo molecular pump, with the stator 10
A rotor (rotating shaft) 12 is rotated around the center.

The rotor is housed in a cylindrical outer cylinder 16 provided with an exhaust port 14 at the bottom in the figure, and stator blades 18 provided on the outer peripheral surface of the outer cylinder 16 are provided on the opposite peripheral surface of the rotor 12. A pumping action is performed by the rotor 120.

The motor coil 22 provided in the stator 10 is excited by an inverter to rotate the rotor 12. At this time, the rotor 12 is magnetically levitated by the axial electromagnet 24, and its attitude is controlled in the radial direction. Electromagnet 2
6.28, respectively.

In order to roughly control the axial position and posture of the rotor 12, the axial position and radial position are measured by the axial position sensor 3.
0. They are detected by radial sensors 32 and 34, respectively.

Further, the rotation speed of the rotor 12 is detected by a rotation speed sensor 36, and in this embodiment, a sensor with a simple structure and stable performance that generates one pulse for each rotation of the rotor 12 is used as the rotation speed sensor 36. has been done.

Note that in this embodiment, the rotor 12 is controlled in five axes, and accordingly, a pair of radial position sensors 32 and 34 are provided.

Here, the connector 38 provided on the lower side of the pump in FIG.
A control circuit for controlling the floating position and attitude of the rotor 12 is connected to the rotor 12, and FIG. 2 shows one axis of a circuit block diagram for controlling the attitude of the rotor 12.

In the figure, the detection signal of the radial position sensor 32 (34) is supplied to one comparison input of a comparator 40, and the other comparison input of the comparator 40 receives a signal corresponding to the reference position of the axis. It is supplied from the reference position setter 42.

The comparison signal of the comparator 40 is supplied to a power amplifier 48 via a preamplifier 44° and a PID compensator 46, and the power amplifier 48 supplies the radial electromagnet 26 (
28> is being energized.

As a result, the rotor 12 is connected to the radial position sensor 32 (34).
The detected position is controlled to move in a direction that matches the reference position by the reference position setter 42, and rotated in the reference posture.

Here, the detection signal of the radial position sensor 32 is supplied to one comparison input of the comparator 40 via a band elimination filter 50.

In the band-pass filter 50, the detection signal of the radial position sensor 32 (34) is supplied to one comparison input of the switched-capacitor type band 1 or pass filter 52 and the comparator 54, and the switched-capacitor type band-pass filter The filter output of 52 is fed to the other comparison input of comparator 54.

Furthermore, the comparison output of the comparator 54 is fed to one comparison input of the comparator 40 and is therefore fed to the bandstop filter 5.
At 0, the component that has passed through the switched capacitor band-pass filter 54 is eliminated from the detection signal of the radial position sensor 32 (34).

Figure 3 shows a switched capacitor type bandpass filter 5.
2, the center frequency fo of its passband shown in FIG. 4 is determined by the frequency of the external clock.

This external clock is the rotation speed sensor 3 in FIG.
This is obtained by multiplying the detection signal of No. 6 by several tens to hundreds of times using the PLL circuit 56. Note that the detection signal of the rotation speed sensor 36 is converted into a square wave by the waveform shaper 58 and then processed by the PLL.
56.

Therefore, in this embodiment, an external clock that accurately follows the rotation of the rotor 12 is applied to the switched capacitor type band pass filter 52, and the switched capacitor type band pass filter 52 is highly responsive to changes in the rotation speed of the rotor 12. The passband center frequency fo is adjusted υJtf
be ffled.

Therefore, the band pass filter 52 similarly controls the cancellation band center frequency fo of the band cancellation filter 52 having the band cancellation characteristic shown in FIG.

As a result, the rotational frequency component of the rotor 12 is removed from the detection signal of the radial position sensor 32 (34>), thereby preventing vibration on the stator 16 side.

Since the center frequency fo is adjusted and controlled by the PLL circuit 56 with high precision in response to changes in the rotor 12, vibrations on the stator 16 side can be effectively prevented regardless of the rate of change in the rotational speed of the rotor 12.

Furthermore, since the rotation speed sensor 36 has a simple structure and stable performance, it is possible to maintain the excellent performance as described above over a long period of time.

As explained above, according to this embodiment, the rotational speed component of the rotor 12 is removed from the detection signal of the radial position sensor 32 (34), and the attitude control of the rotor 12 is performed using the detection signal. Vibration on the stator 16 side can be prevented.

Therefore, in an electron microscope using this pump, highly accurate measurements are possible.

(Effects of the Invention) As explained above, according to the present invention, the rotation speed frequency component is removed from the radial position detection signal of the rotating shaft used for attitude control of the magnetically levitated rotating shaft. It becomes possible to reliably prevent and suppress vibrations.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the internal structure of the magnetic bearing type turbomolecular pump, Fig. 2 is an explanatory diagram of the rotor attitude control circuit in Fig. 1, and Fig. 3 is an explanatory diagram of the circuit configuration of the switched capacitor type pass filter in Fig. 2. 4 is a filter characteristic diagram of the switched capacitor type bandpass filter 52 in FIG. 2, and FIG. 5 is a filter characteristic diagram of the band-elimination filter 50 in FIG.
FIG. 10... Stator 12... Rotor 26.28... Radial electromagnet 32.34... Radial position sensor 36... Rotation speed sensor 40... Comparator 42... Reference position setter 44... Preamplifier/16... PID compensator/18... Power amplifier 50... Band elimination filter 52... Switched capacitor type band pass filter 54... Comparator 56... PLL Circuit 58...Waveform shaper or more Applicant: Seiko Seiki Co., Ltd. Full Huff ttb9qFrst good figure 4

Claims (1)

[Claims] (1) Shaft radial position detection means for detecting the radial position of the magnetically levitated rotary shaft; shaft movement control means for moving the rotary shaft in a direction in which the detected position coincides with a target position; and rotation of the rotary shaft. A magnetic bearing type turbomolecular pump comprising: a shaft rotation speed detection means for detecting the number of rotations; and a shaft rotation speed component removal means for removing a component corresponding to the detected rotation speed from an amount corresponding to the detected position of the shaft movement control means. Rotary axis attitude control device.