JP5498171B2 - High speed rotary vacuum pump - Google Patents

Abstract

A rapidly rotating vacuum pump includes: a magnet-mounted rotor driven by an electric drive motor with a predetermined constant nominal rotational frequency (fnom). The rotor and a rotor bearing are embodied in such a way that the bending-critical counter-rotational resonance frequency (fcrit) is between 3% and a maximum of 30% above the nominal rotational frequency (fnom), thereby preventing an overspeed.

Description

  In high-speed rotary vacuum pumps, in other words non-volume type, especially magnetically supported turbomolecular pumps, rotational speeds in the range of overspeed not only cause centrifugal pump failure due to centrifugal force. Since it can pose considerable danger to people, it is necessary to reliably prevent overspeed.

  In practice, the overspeed of a high-speed rotary vacuum pump can cause a complex electronic assembly that operates to monitor the rotational speed of the rotor and the electric drive motor for the rotor and determine the rotational speed limit by electronic means. It is prevented by using. In this way, the realization of safe active overspeed prevention for high speed rotary vacuum pumps is possible with high technical costs and a lot of hardware and software, but the resulting high technical costs are considerable. Causes costs.

European Patent Application No. 0333200

  An object of the present invention is to provide a high-speed rotary vacuum pump equipped with a simple and reliable overspeed prevention means.

  According to the invention, the above object is achieved by the features of claim 1.

  In the high speed rotary vacuum pump of the present invention, the rotor is designed such that the flexural critical anti-rotation resonance frequency exceeds the nominal speed between 3% and up to 30%. No active overspeed prevention means is provided, that is, no means for directly controlling and limiting the rotational speed other than the control means for the electric drive motor is provided.

  The process of setting the deflection critical anti-rotation resonance frequency to exceed the nominal rotation speed between 3% and maximum 30% can be performed in various ways. In particular, the mass, shape and support of the vacuum pump rotor can be modified and adapted so that the deflection critical anti-rotation resonance frequency exceeds the nominal rotational speed by up to 30%, thereby exceeding it inherently Prevent speed. Resonant vibration at the flexural critical anti-rotation resonance frequency consumes considerable power so that the above level of rotation can only be achieved with a large accumulation of power. The drive power of the electric drive motor needs to be set so that the drive power of the electric drive motor can be completely consumed by the resonance vibration at the rotational speed within the range of the deflection critical anti-rotation resonance frequency. Therefore, faults are effectively ruled out because an inherent overspeed prevention means is generated by the hardware. Since the cost for active overspeed prevention can be eliminated, the cost for overspeed prevention can be significantly reduced.

  In contrast to the rigid critical resonance frequency, which is relatively low, usually passed fast and with relatively little power storage, the deflection critical frequency is at a relatively high frequency level. For this reason, the deflection critical anti-rotation resonance frequency is particularly suitable for being utilized for inherent overspeed protection.

  The rotor of the vacuum pump is supported by a magnetic bearing. A magnetic bearing is to be understood here as a magnetic bearing with at least one radial degree of freedom. In practice, however, when a magnetic bearing is provided, the rotor of the high speed rotary vacuum pump is magnetically supported for all five degrees of freedom. During operation, the magnetic bearing itself generates radial vibrations of the rotor with balance control. This also excites vibrations, particularly at the flexural critical resonance frequency. Unless an appropriate magnetic support control algorithm is provided to pass the flexural critical resonance frequency, it is impossible for the pump to pass these vibrations. Such an appropriate control algorithm is not provided here. Instead, the magnetic support control algorithm is configured so that, based on the available drive energy, the pump is deflected and cannot pass the critical resonance frequency.

  The deflection critical anti-rotation resonance frequency is preferably greater than 5% to 25% of the nominal rotational speed, and more preferably within a range exceeding 20% of the nominal rotational speed. Being about 20% above the nominal speed prevents the rotor from overshooting during the process of raising the rotor from stop to nominal speed, providing sufficient safety. Accordingly, it is possible to avoid improperly causing the generation of the bending critical anti-rotation resonance frequency due to the overshoot during the climb. On the other hand, the flexural critical anti-rotation resonance frequency should be as close as possible to the nominal speed, thus eliminating the rotor design requirements that require unnecessarily high stability. .

  The high-speed rotary vacuum pump is preferably a non-volumetric vacuum pump, such as a turbomolecular vacuum pump. For turbomolecular vacuum pumps, the rotational speed is usually in the range of 10,000 to 100,000 r / min. In such a high range of rotation speed and speed, it is particularly desirable to use a magnetic bearing to support the rotor.

  The invention is explained in more detail below with reference to the drawings.

A so-called Campbell diagram of a high-speed rotary vacuum pump is shown.

In the Campbell diagram shown in FIG. 1, the resonance frequency f _res of the rotor is shown with respect to the rotation speed f _{rot of the} rotor.

The high-speed rotary vacuum pump in this embodiment is a turbo molecular vacuum pump, and the rotor of this vacuum pump is completely supported by a magnetic bearing in a five-axis configuration. The rotor is driven by an electric drive motor and is operated at a preset constant nominal speed f _nom .

In FIG. 1, first, two rigid body critical resonance frequency curves 12 and 14 are respectively shown in a lower rotational speed range. These resonance frequencies change only to a relatively small extent with the rotational speed f _rot of the rotor. Furthermore, a curve 16 representing the deflection critical anti-rotation resonance frequency and a curve 18 representing the deflection critical co-rotation resonance frequency are shown in the higher rotation speed range. Furthermore, a so-called position vector 20 is indicated by a broken line. At the point where the position vector 20 intersects the deflection critical anti-rotation resonance frequency curve 20, the deflection critical anti-rotation resonance frequency f _crit for the vacuum pump of the present invention can be read.

In this example, the deflection critical anti-rotation resonance frequency f _crit for the vacuum pump rotor is approximately 970 Hz. The nominal speed f _nom of the vacuum pump, the electric drive motor for the vacuum pump, the controller of the electric drive motor and the rotor is approximately 800 Hz. Therefore, the deflection critical anti-rotation resonance frequency f _crit exceeds the nominal rotation speed f _nom of the vacuum pump by approximately 21%.

The drive power of the electric drive motor is limited so that the drive power is completely consumed by the anti-rotation resonance frequency when the rotational speed of the rotor is bent and accidentally reaches the critical anti-rotation resonance frequency _fcrit .

  The vacuum pump is not provided with further active overspeed prevention means, that is, the vacuum pump is not provided with a second rotational speed control loop in addition to the motor-controlled rotational speed control loop.

  The curve 16 representing the deflection critical anti-rotation resonance frequency cannot be affected by the corresponding setting of the control parameters of the vacuum pump magnetic bearing. However, the control parameters of the magnetic bearing are set so that the deflection critical resonance frequency is excited sufficiently strongly in order to exclude the possibility of the pump bending and passing the critical resonance frequency by operation with available drive energy. For this, the control parameters for the magnetic bearing need to be relatively fluid.

Claims (4)

In a high-speed rotary vacuum pump with a rotor driven by an electric drive motor and having a preset constant nominal rotational speed,
The rotor is supported by a magnetic bearing ;
The rotational direction before Symbol rotor resonant frequency of the whirling motion in the opposite direction, and beyond the nominal rotational speed of 3% to between up to 30 percent,
There is no active overspeed prevention means,
A high-speed rotary vacuum pump characterized in that the drive power of the electric drive motor is set so that it can be consumed by resonance vibration at a rotation speed within the range of the resonance frequency.   The high-speed rotary vacuum pump according to claim 1, which is designed as a non-volumetric vacuum pump.   The high-speed rotary vacuum pump according to claim 2, wherein the high-speed rotary vacuum pump is a turbo molecular pump.   The high-speed rotary vacuum pump according to any one of claims 1 to 3, wherein the resonance frequency exceeds the nominal rotational speed by between 5% and 25%.

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