Matsushita Electric Industrial Co., Ltd.

Masakazu Nakashima

Akira Takara

Tohru Nakagawa

Toru Nakagawa

In a magnetic bearing carrying a rotary shaft in the air, the rotary shaft is required to rotate substantially at the same position. In controlling the position of the rotary shaft, a first exciting current I.sub.f is supplied to a plurality of first electric magnets formed in the proximity of one end of the rotary shaft, whereas a second exciting current I.sub.r is supplied to a plurality of second electric magnets formed in the proximity of the other end of the rotary shaft. The first exciting current I.sub.f is represented by the sum of a first biasing current I.sub.f, a first control current i.sub.Hf for translation, and a first control current i.sub.Kf for rotary motion. The second exciting current I.sub.r is represented by the sum of a second biasing current I.sub.r, a second control current i.sub.Hr for translation, and a second control current i.sub.Kr for rotary motion. Under such conditions, a ratio I.sub.f /I.sub.r between the first and second biasing currents, a ratio i.sub.Hf /i.sub.Hr between the first and second control currents for the translation, and a ratio i.sub.Kf /i.sub.Kr between the first and second control currents for the rotary motion are appropriately determined so as not to cause a mutual interference between the translation and the rotary motion of the rotary shaft.

Method of controlling position of rotary shaft in magnetic bearing

A control apparatus of a magnetic bearing controls electromagnets so that both a displacement deviation of a center of gravity of a rotary shaft and an angle of twist around the center of gravity of the rotary shaft become 0, thereby supporting the rotary shaft in space by the magnetic force of the electromagnets. The apparatus includes .theta..sub.X and .theta..sub.Y control devices for controlling angles .theta..sub.X and .theta..sub.Y of twist of the two degrees of freedom of a rotational motion orthogonal to each other around the center of gravity and perpendicular to an axial direction of the rotary shaft, a cross feedback being produced so that both a feedback signal of the rotary angle .theta..sub.X and a feedback signal of the rotary angle .theta..sub.Y are respectively fed back as cross feedback signals to the .theta..sub.Y and .theta..sub.X control devices. A rotational speed detecting device for detecting a rotational number of the rotary shaft. Each of the control devices includes a break frequency and gain value varying device which has a break frequency not larger than a reply frequency of the entire control apparatus with respect to the cross feedback signal, the varying device varying the break frequency of the lowpass filter in inverse proportion to the rotational speed of the rotary shaft, and varying a gain value of the cross feedback signal in proportion to the detected rotational speed of the rotary shaft.

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Neyagawa, Japan

Masakazu Nakashima