Supports – With condition responsive control means
Reexamination Certificate
1998-07-23
2001-02-27
King, Anita M. (Department: 3632)
Supports
With condition responsive control means
C267S136000, C188S378000
Reexamination Certificate
active
06193206
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an active vibration isolator which is suitable for cut-off and suppression of microvibrations of precision instruments, e.g., in a factory for manufacturing semiconductor or a factory for manufacturing products using laser.
DESCRIPTION OF THE PRIOR ART
Japanese Unexamined Patent Publication No. 5-149379 discloses an active vibration isolator which employs a piezoelectric element. The active vibration isolator has a basic configuration of a feedback control loop, which comprises a spring-mass system of one degree of freedom employing spring means having thin elastic bodies and metal plates laminated alternately and having a high rigidity for compression and a low shear rigidity and comprises an actuator employing the piezoelectric element.
In addition, an active vibration isolator having an intermediate mass element interposed in a spring-mass system has been proposed. The active vibration isolator has a basic configuration of a feedback control loop, in which a detection value of vibratory state of the intermediate mass element is employed as a feedback signal such that a piezoelectric element coupled directly to the intermediate mass element is driven on the basis of this feedback signal.
The vibration isolating performance of the above-mentioned active vibration isolators in a high-frequency region depends on the passive vibration isolating characteristic, and therefore problems which will be described below arise in the cut-off and suppression of the microvibrations of precision instruments or the like, in the case that vibration isolation, e.g., of about −60 dB (transmissibility of vibration of −60 dB) is required at a frequency, e.g., in the vicinity of 300 Hz.
In order to achieve vibration isolation of about −60 dB at a frequency in the vicinity of 300 Hz, a resonance point of the vibration system including the active vibration isolator and an object to be isolated from vibration should be set at in the vicinity of 3 to 4 Hz, as shown by a curve II (dashed line) in FIG.
8
. For this purpose, the amplitude of the piezoelectric element has to be increased and the spring constant of the spring means has to be decreased. However, the stroke of the piezoelectric element is limited and therefore it is practically impossible to make the above vibration system compatible with the resonance point in a low-frequency area not more than 10 Hz by the piezoelectric element. On the other hand, decreasing the spring constant disadvantageously increases the amplitudes of the vibrations of the object.
In a spring-mass system of one degree of freedom, accordingly, the limit of the setting of the resonance point is in the vicinity of 15 Hz (this value depends on the amplitude of the actuator) at best, as shown by a curve III (chain line) in
FIG. 8
, and thus a sufficient vibration isolating performance in the high-frequency region cannot be obtained.
In a spring-mass system of two degrees of freedom, as shown by a curve IV (two-dot chain line) in
FIG. 8
, the vibration isolating performance in the high-frequency region is improved, while there occur two resonance points.
SUMMARY OF THE INVENTION
The invention, which has been done in order to eliminate such problems of the prior arts, is intended to provide an active vibration isolator which prevents any resonance points from appearing in the low-frequency region and provides a sufficient vibration isolating performance in the high-frequency region.
In order to achieve the above-mentioned object, in accordance with a first aspect of the invention, an active vibration isolator comprises an intermediate mass element placed in the space between an object to be isolated from vibration and a supporting surface; a first elastic member having one end fixed to the intermediate mass element and the other end fixed to the object and exerting spring action on the intermediate mass element and the object; a solid element or a fluid element placed between the intermediate mass element and the supporting surface and, with respect to an acting direction along its length that varies with a variation in voltage, magnetic field generated in the solid element, or air pressure generated in the solid element, having one end fixed to the supporting surface or having the other end fixed to the intermediate mass element; a second elastic member placed between the intermediate mass element and the solid element or between the solid element and the supporting surface and exerting spring action on the intermediate mass element, directly or indirectly through the solid element; a power input portion for causing the variation in voltage, magnetic field in the solid element, or air pressure in the fluid element; a first sensor for detecting the vibratory state of the object with respect to the acting direction; a second sensor for detecting the vibratory state of the intermediate mass element with respect to the acting direction; and a controller for receiving signal input from the first sensor and from the second sensor, and for outputting to the power input portion a signal which causes the variation in voltage, magnetic field, or air pressure such that the intermediate mass element vibrates to cancel out the vibrations of the object in the acting direction.
In accordance with a second aspect of the invention, an active vibration isolator comprises an intermediate mass element placed in the space between an object to be isolated from vibration and a supporting surface; a first elastic member having one end fixed to the intermediate mass element and the other end fixed to the object and exerting spring action on the intermediate mass element and the object; a linear motor placed between the intermediate mass element and the supporting surface and, with respect to an acting direction along its length that varies with a variation in magnetic field, having one end fixed to the supporting surface and the other end fixed to the intermediate mass element, and having spring action; a power input portion for causing the variation in magnetic field in the linear motor; a first sensor for detecting the vibratory state of the object with respect to the acting direction; a second sensor for detecting the vibratory state of the intermediate mass element with respect to the acting direction; and a controller for receiving signal input from the first sensor and from the second sensor, and for outputting to the power input portion a signal which causes the variation in magnetic field such that the intermediate mass element vibrates to cancel out the vibrations of the object in the acting direction.
In accordance with a third aspect of the invention, an active vibration isolator comprises an intermediate mass element placed in the space between an object to be isolated from vibration and a supporting surface; a first elastic member having one end fixed to the intermediate mass element and the other end fixed to the object and exerting spring action on the intermediate mass element and the object; a pneumatic actuator placed between the intermediate mass element and the supporting surface and, with respect to an acting direction along its length that varies with a variation in air pressure generated inside thereof, having one end fixed to the supporting surface and the other end fixed to the intermediate mass element, and having spring action; a power input portion for causing the variation in air pressure in the pneumatic actuator; a first sensor for detecting the vibratory state of the object with respect to the acting direction; a second sensor for detecting the vibratory state of the intermediate mass element with respect to the acting direction; and a controller for receiving signal input from the first sensor and from the second sensor, and for outputting to the power input portion a signal which causes the variation in air pressure such that the intermediate mass element vibrates to cancel out the vibrations of the object in the acting direction.
In accordance with a fourth aspect of the invention, the c
Itojima Fumiaki
Tsuchiya Masaki
Yasuda Masashi
King Anita M.
Ostrolenk Faber Gerb & Soffen, LLP
Tokkyokiki Corporation
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