FreshPatents Logo
newTOP 200 Companies
filing patents this week


High rotational speed vacuum pump

Abstract: A high rotational speed vacuum pump includes a compressor , a drive motor for driving said compressor , and a motor control unit for operating said drive motor at a constant nominal rotational frequency. Depending on the basic conditions, undesirably strong oscillations may occur at the compressor during compressor operation at the nominal rotational frequency. These undesirably strong oscillations cause the bearings to be excessively stressed. To reduce the oscillation stress of the compressor and/or the vacuum pump, an activatable rotational frequency correction device is associated with the motor control unit . The correction device constantly corrects the nominal frequency by a rotational frequency correction value of max. 10% of the nominal rotational frequency when the rotational frequency correction device is activated. This allows the rotational frequency of the drive motor to be changed in a simple manner when strong natural oscillations of the compressor and/or the vacuum pump occur such that resonance effects and the like can be avoided.


Browse recent patents
Inventors:

Temporary server maintenance - Text only. Please check back later for fullsize Patent Images & PDFs (currently unavailable).

The Patent Description data below is from USPTO Patent Application 20090202360 , High rotational speed vacuum pump

BACKGROUND

The invention relates to high rotational speed vacuum pumps, for example turbomolecular pumps.

SUMMARY

In the present case, the term high rotational speed vacuum pump relates to vacuum pumps with nominal speeds as from 10,000 revolutions per minute. High rotational speed vacuum pumps, for example turbolmolecular pumps, are normally operated at a constant nominal rotational speed or nominal rotational frequency. The nominal rotational frequency is determined such that the resonant frequency or the resonant frequencies of the vacuum pump are not excited. While the nominal rotational frequency at which the motor control unit operates the drive motor virtually remains unchanged and constant, the resonant frequencies of the vacuum pump may change depending on numerous basic conditions. The resonant frequency of the vacuum pump is in particular influenced by changes of the vacuum pump mass, suspension and damping. In plants comprising a plurality of high rotational speed vacuum pumps which are all mounted on a single frame and are thus mechanically interconnected, the vacuum pump oscillations having the same frequency may combine into oscillations with a large amplitude, and/or the resonant frequency of one or a plurality of vacuum pumps may change such that the respective vacuum pump is excited by a vacuum pump operating at the nominal rotational frequency. Studies have shown that wear of vacuum pump bearings used in this type of plant is to a large extent caused by the effects described above.

DETAILED DESCRIPTION

It is an object of the invention to provide a possibility of reducing the wear caused by natural oscillations of high rotational speed vacuum pumps.

According to one aspect, an activatable rotational frequency correction device is associated with the motor control unit, said correction device constantly correcting the nominal rotational frequency by a rotational frequency correction value of max. 10% of the nominal rotational frequency when the rotational frequency correction device is activated. Provision of the rotational frequency correction device allows the per se constant rotational frequency to be slightly changed. In this manner, the rotational frequency of the drive motor can be slightly adjusted preemptively or according to requirement, which normally is an adequate measure for eliminating resonance behavior of the vacuum pump at the nominal rotational frequency, or prevent the generated oscillations from summing up and building up when a plurality of vacuum pumps are mounted on a common frame. For this purpose, a rotational frequency correction value of max. 10% of the nominal rotational frequency is completely sufficient. Normally, even a rotational frequency correction value of 0.5-2% of the nominal rotational frequency suffices for preventing the occurrence of resonance and/or a build-up of oscillations. In this manner, in particular wear of the bearings is reduced.

Preferably, a rotational frequency correction activator is provided which may be connected to the rotational frequency correction device for activating the latter. The rotational frequency correction activator may be an external electronic storage element, for example, which is adapted to be electrically connected to the rotational speed correction device. Once the rotational frequency correction activator is connected to the rotational speed correction device, the nominal rotational frequency is reduced by a value stored in the rotational speed correction device or in the rotational frequency correction activator.

The external electronic storage element may be configured as a dongle, for example, which is connectable to an electric interface of the motor control unit and/or the rotational frequency correction device. Connecting the dongle to the interface causes the rotational speed to be corrected in a simple manner. Storage elements and/or dongles with different rotational speed correction values may be provided such that the value and the sign of adjustment of the nominal rotational frequency can be selected.

According to a preferred aspect, an oscillation sensor connected to the rotational frequency correction device is associated with the compressor, wherein the rotational frequency correction device is activated when the oscillation sensor detects that a predetermined oscillation amplitude of the compressor has been exceeded. Provision of an oscillation sensor and evaluation of the oscillation signal provided by said oscillation sensor allow the vacuum pump to be permanently monitored. Thus the vacuum pump is virtually maintenance-free with regard to prevention of strong natural oscillations. Further, it is thus ensured that a rotational frequency correction is performed when the resonant frequency of the vacuum pump changes in a critical manner only after startup of the vacuum pump.

Preferably, at least two different rotational frequency correction values are stored in the rotational frequency correction device. In this manner, a second rotational frequency correction can be performed, in particular in plants comprising a plurality of vacuum pumps mounted on a common frame, if the first rotational frequency correction turns out to be inadequate.

According to a preferred aspect, a control device is associated with the rotational frequency correction device, said control device receiving the controlled variable from the oscillation sensor. The rotational frequency is the manipulated variable. The control device ensures, in particular in complex systems comprising a plurality of vacuum pumps, that a rotational frequency correction is performed even under temporarily changing basic conditions, said rotational frequency correction ensuring the smallest possible oscillation of the vacuum pump and/or the compressor.

Generally, the control device may be provided both in the vacuum pump itself and, in particular in plants comprising a plurality of vacuum pumps, centrally in a control unit common to all vacuum pumps.

A method according to the invention for operating a high rotational speed vacuum pump having a compressor, a drive motor for driving the compressor, and a motor control unit for operating the drive motor at a constant nominal rotational frequency, comprises the following method steps:

The method according to the invention allows the natural oscillations of the compressor to be automatically monitored and the frequency of the oscillations generated by the drive motor to be corrected, if necessary.

The vacuum pump ; comprises a turbomolecular compressor driven by a drive motor . The drive motor may be a direct current or an alternating current motor.

The drive motor is driven by a motor control unit which supplies current to the motor windings. The motor control unit operates the drive motor at a constant rotational frequency.

The vacuum pump shown in further comprises a rotational frequency correction device adapted to be activated by a rotational frequency correction activator . The activated rotational frequency correction device causes the motor control unit to adjust the nominal rotational frequency, e.g. to adjust the rotational frequency by a rotational frequency correction value of 10 Hz.

The rotational frequency correction activator is an electronic storage element configured as a so-called dongle. The dongle is connected to a parallel or serial interface , when necessary, said interface being connected to the rotational frequency correction device . In the rotational frequency correction activator the rotational frequency correction value is electronically stored.

When the rotational frequency correction activator is not connected to the interface , the rotational frequency correction device is not activated such that the motor control unit operates the drive motor at the nominal rotational frequency. Once the rotational frequency correction activator is connected to the interface of the rotational frequency correction device , the rotational frequency is reduced by the stored value.

In the embodiment shown in of a vacuum pump , the oscillation behavior of the vacuum pump is controlled by controlling the rotational frequency of the drive motor . For this purpose, an oscillation sensor is fixed to the compressor , said sensor sensing the frequency and the amplitude of the natural oscillations of the compressor . The oscillation sensor may also be arranged at a housing portion of the vacuum pump .

The oscillation sensor is connected to the rotational frequency correction device which evaluates the oscillation information supplied by the oscillation sensor and causes the rotational frequency to be corrected when the oscillation sensor detects that a predetermined oscillation amplitude of the compressor has been exceeded. If the oscillation sensor detects too strong oscillations, the rotational frequency correction device performs an upward or downward correction of the nominal rotational frequency by a rotational frequency correction value of 10 Hz to obtain a new motor rotational frequency. If the oscillation sensor detects inadmissibly high oscillations when the drive motor is operated at the new motor rotational frequency, the nominal rotational frequency is changed by a second rotational frequency correction value, and the drive motor is operated at the second new motor rotational frequency.

In the rotational frequency correction device a control device may be provided which receives the controlled variable from the oscillation sensor . The motor rotational frequency may also be infinitely variable such that the motor rotational frequency always lies as close to the nominal rotational frequency as possible.

The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.