Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1986-01-10
1987-08-11
Skudy, R.
Electrical generator or motor structure
Dynamoelectric
Rotary
74 56D, 318629, F16C 3906
Patent
active
046864040
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic bearing device, and particularly to a controlled radial magnetic bearing device.
Magnetic bearings of a controlled type have recently been used for spindles of machine tools, turbo-molecular pumps, etc. which are driven at a high speed e.g. 30,000-40,000 r.p.m. or higher. As one of such magnetic bearings, a controlled radial magnetic bearing is known.
The bearing of this type generally includes an electromagnet for the X-axis and an electromagnet for the Y-axis provided in X- and Y-axis directions perpendicular to each other in a plane normal to the axis of the rotary shaft to magnetically support the rotary shaft; position sensors for X-axis and Y-axis are disposed on the X-axis and Y-axis, respectively, to detect any displacement of the rotary shaft in the X-axis and Y-axis directions from a reference position, and control circuits are provided for the X-axis and Y-axis for feeding the outputs of the position sensors back to the electromagnets and thereby controlling the outputs of the electromagnets.
With such a magnetic bearing device, the electromagnetic forces of the electromagnets for the X-axis and Y-axis are controlled by detecting any displacement of the rotary shaft in the X-axis and Y-axis directions by means of the position sensors, and then amplifying any differences from reference values preset in the control circuits, and then phase-compensating them, and then amplifying the outputs.
In case such a conventional controlled magnetic bearing device is used with a spindle of a turbo-molecular pump, for example, a fin rotor mounted on the spindle increases the inertia moment, so that as the speed of rotation increases, the gyroscopic moment sometimes generates a reverse precession in a direction reverse to the rotation of the spindle (as shown in FIG. 2).
Such a precession can be restrained by increasing the gain of the control system and the dynamic rigidity. However, the increase of gain has a disadvantage of requiring a higher voltage for control and causing increased vibration during rotation.
SUMMARY OF THE INVENTION
An object of the present is to provide a controlled radial magnetic bearing device which can effectively suppress the precession of a rotary shaft without increasing the gain of the control system or dynamic rigidity.
Another object of the present invention is to provide a magnetic bearing device which has a control circuit for controlling the position of the axis of a rotary shaft, the control circuit comprising correction circuits for adjusting the outputs of the position sensors for the X-axis and Y-axis so that one of the outputs will lead in phase by 90 degrees with respect to the other output, thereby attenuating the precession of the rotary shaft electrically.
In accordance with the present invention, there is provided a controlled radial magnetic bearing device having an electromagnet for the X-axis and an electromagnet for the Y-axis provided on the X-axis and Y-axis perpendicular to each other in a plane normal to the axis of a rotary shaft for magnetically supporting the rotary shaft, position sensors for the X-axis and Y-axis provided on the X-axis and Y-axis for detecting any displacement of the rotary shaft from its reference position in the X-axis and Y-axis directions, respectively, and control circuits for the X-axis and Y-axis for feeding the outputs of said position sensors back to said electromagnets and thereby controlling the outputs of said electromagnets, characterised in that it further comprises a speed detecting means for each of said control circuits for detecting the speed of rotation of the rotary shaft, a correction circuit for the X-axis comprising a band-pass filter for taking extracting the frequency component of the reverse precession from the output of the position sensor for of phase by 90 degrees, to control the position of the rotary shaft in the X-axis direction, a changing means for changing the output of said band-pass filter according to the output of said spee
REFERENCES:
patent: 3787100 (1974-01-01), Habermann
patent: 4121143 (1978-10-01), Habermann
patent: 4417772 (1983-11-01), Robinson
patent: 4473259 (1984-09-01), Goldowsky
Nakazeki Tsugito
Nanami Shoji
Okada Koichi
NTN Toyo Bearing Co. Ltd.
Skudy R.
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