Electromagnetically suspended floating floor apparatus

Abstract: An electromagnetically suspended floating floor apparatus in which a floating floor (24) on which machines are set up is suspended from an installation floor with electromagnetic actuators so that the floating floor is spacially separated from the installation floor whereby no vibration is transmitted to the equipment. The floating floor apparatus comprises the floating floor suspended from the installation floor at a plurality of supporting points by electromagnetic actuators (2), a light emitting member (25) fixed to a beam or a pillar and which emits a horizontal light beam, and a photosensor (26) fixed to the installation floor and which outputs a position signal representing a position of incidence of the horizontal light beam to the electromagnetic actuators. On the basis of the position signal, the electromagnetic actuators control a vertical position of the floating floor.

Description: The present invention relates to an electromagnetically suspended floating floor apparatus, and particularly to an electromagnetically suspended structure which is spacially separated from beams and pillars of a building by magnetically suspending the floor to avoid vibration thereof. Equipment such as an electromicroscope and a semiconductor manufacturing apparatus which must be isolated from vibration are usually mounted on a vibration eliminating apparatus when installed in a factory. A vibration eliminating apparatus using a magnetic suspending system which has an excellent vibration eliminating capability has been developed replacing a conventional apparatus utilizing pneumatic springs or rubber, and details of such a vibration eliminating apparatus are given, for example, in Japanese Patent Laid-open No. 203040/92. Fig. 1 illustrates an example of a conventional vibration eliminating apparatus using a magnetic suspending system. Equipment such as an electromicroscope or a semiconductor manufacturing apparatus which must be isolated from vibration (not illustrated) is mounted on a vibration eliminating table 1 which is maintained in a suspended state by means of an electromagnetic actuator 2. Therefore, even if an installation floor (not shown), on which the electromagnetic actuator 2 is installed, is caused to vibrate by an earthquake or the like, no vibration is transmitted to the suspended vibration eliminating table 1 and therefore equipment which is installed on said table 1 is not affected by the vibration of the installation floor. Fig. 2 is an explicative diagram of an electromagnetic actuator 2 of the vibration eliminating apparatus illustrated in Fig. 1. On the vibration eliminating table 1 on which a machine may be mounted, a yoke 3 consisting of a magnetic material is fixed. Electromagnets 4 fixed to the installation floor 6 suspend the magnetic yoke 3 fixed to the vibration eliminating table 1 with a magnetic attracting force. A gap between a pole of the electromagnet 4 and the magnetic yoke 3 to be suspended as a target can be measured with a displacement sensor 5. A controller 7 comprises a compensating circuit 9 and a power amplifier 10 used to control an excitation current provided to the electromagnet 4 so that the vibration eliminating table 1 and the magnetic yoke 3 can be stably suspended in a target position on the basis of the output from the displacement sensor 5. Since such a vibration eliminating apparatus as explained above is provided for each piece of sensitive to vibration, any chance to the configuration of the said apparatuses within the installation room, entails carrying out modifications to the housing it. Moreover, in a semiconductor manufacturing factory, for example, such a problem occurs that it is difficult to make modifications to change the arrangement of vibration eliminating apparatuses since such facilities are often replaced due to rapid technical innovation. The present invention has been proposed to overcome the disadvantages of the prior art, and it is an object of the present invention to provide a floating floor apparatus on which sensitive equipment which must be isolated from any vibration can be freely arranged without any change in arrangement of a vibration eliminating apparatus. A floating floor apparatus of the present invention comprises the features of independent claim 1. The floating floor is suspended by the actuators at the supporting points and separated spacially from the installation floor. Therefore, no vibrations in the installation floor are transmitted to equipment mounted on the floating floor. In order to keep the whole part of the floating floor in a horizontal level, the photosensor means fixed to the floating floor receives a horizontal light beam and detects a vertical position of the floating floor with reference to the horizontal light beam so that the actuators can adjust a vertical position of the floating floor. Fig. 1 is a perspective view schematically illustrating the structure of an existing vibration eliminating apparatus; Fig. 2 shows a section of an existing electromagnetic actuator and a block diagram of a control unit for the actuator; Fig. 3 is a sectional view schematically illustrating the structure of a preferred embodiment of an electromagnetically suspended floating floor apparatus to which the present invention is applied; Fig. 4 shows a section of the electromagnetic actuator shown in Fig. 3 and a control unit for the actuator; and Fig. 5 is a diagram indicating a positional relationship between a light emitting member and a photosensor in the electromagnetic floating floor shown in Fig. 3. Fig. 3 illustrates a concept of a preferred embodiment of an electromagnetically suspended floating floor apparatus according to the present invention. An electromagnetically suspended floating floor 24 on which a plurality of machines such as electromicroscopes or semiconductor manufacturing apparatuses which must be isolated from vibration can be mounted is provided within a chamber 21 divided by pillars 22 and a beam 23. Such an electromagnetically suspended floating floor structure is suspended by the electromagnetic actuators 2 at a plurality of supporting points 31 resulting in being separated spacially from a building. Fig. 4 is a diagram for explaining details of a preferred embodiment of an electromagnetically suspended floating floor apparatus of the present invention. The structure of the electromagnetic actuator 2 supporting the floating floor 24 at one of the supporting points 31 is similar to that of the electromagnetically controlled actuator of the existing vibration eliminating apparatus shown in Fig. 2. Specifically, the magnetic yoke 3 is fixed to the floating floor 24 at the supporting point 31 and the magnetic yoke 3 is suspended by virtue of the magnetic attracting force of the electromagnet 4 fixed to the installation floor 6. One of the pillars 22 of the building adjacent to the actuator 2 is provided with a light emitting member 25 consisting of a laser light emitting element which can emit a light beam in the horizontal direction. A photosensor 26 which outputs a position signal representing a vertical position of the yoke 3 in accordance with a position irradiated with the light beam emitted from the light emitting member 25 is fixed to the magnetic yoke 3 suspended by the electromagnetic actuator 2. A position signal outputted from the photosensor 26 indicates a displacement of the yoke 3 from the horizontal light beam serving as a reference position of the floating floor 24 at the supporting point 31. Such a position signal is amplified by an amplifier 28 and then inputted to a compensation circuit 9. The amplified position signal undergoes phase and gain adjustment in the compensation circuit 9, is then amplified by the power amplifier 10 and changes an exciting current to the electromagnet 4. The position of the floating floor 24 can be adjusted to return to the reference position with a magnetic attracting force generated by the electromagnet 4 depending on a level of exciting current applied thereto. The pillar opposing to the light emitting member 25 is provided with a light receiving element 27 to confirm if the light beam emitted from the light emitting member 25 is in the horizontal direction. The electromagnetic actuator 2 which suspends the floating floor 24 at each supporting point 31 operates such as explained hereunder. Since the electromagnet 4 suspends the magnetic yoke 3 with a magnetic attracting force, the floating floor 24 is suspended by the electromagnetic actuator 2 at the supporting point 31 and is spacially separated from the building. For example, if a position of a part of the installation floor 6 is changed in a vertical direction, the position where the horizontal light beam from the light emitting member 25 impinges the photosensor 26 also changes. As a result, the photosensor 26 outputs a voltage corresponding to the position at which the light beam is incident. The exciting current fed to the electromagnet 4 is controlled through the compensation circuit 9 and the power amplifier 10 based on an output voltage of the photosensor 26, namely, a position signal which indicates a detected displacement of the yoke 3 in the vertical direction, thereby forcing the magnetic yoke 3, namely the floating floor 24, to move up or move down to the reference position at the supporting point 31. Therefore, even if a relative position of the floating floor 24 changes due to a positional change in the installation floor 6 or other reasons, the floating floor 24 is controlled to return to the reference position, maintaining the entire floating floor in a horizontal position. The floating floor 24 is also provided with a first acceleration sensor 29, while the installation floor 6 is provided with a second acceleration sensor 30. Signals detected by these acceleration sensors 29, 30 are inputted to the compensation circuit 9 to generate a compensation signal which is in turn power-amplified by the power amplifier 10 and then applied to the electromagnet 4 as a portion of the exciting current. The compensation circuit 9 operates to control the floating floor 24 to damp (attenuate) vibration thereof in accordance with acceleration detected by the acceleration sensors 29, 30. Specifically, if any external force is applied to the supporting point 31 where the electromagnetic actuator 2 suspends the floating floor 24, the first acceleration sensor 29 detects acceleration caused by the external force and the compensation circuit 9 and the power amplifier 10 cause the electromagnet 4 to generate a magnetic attracting force whereby the external force applied to the floating floor 24 is cancelled and the floating floor 21 is maintained at the predetermined reference position. Similarly, if an external force is applied to the installation floor 6, acceleration caused by the external force applied to the installation floor 6 is detected by the second acceleration sensor 30. The output of the second acceleration sensor 30 is fed back to the electromagnet 4 as the exciting current through the compensation circuit 9 and the power amplifier 10. Accordingly, the floating floor 24 is controlled to quickly attenuate the vibration. Fig. 5 is a plan view of a preferred embodiment of an electromagnetically suspended floating floor apparatus to which the present invention is applied. A multiplicity of electromagnetic actuators 2 are arranged in the chamber 21 and the floating floor 24 is suspended at the supporting points by the electromagnetic actuators 2. The pillar 22 of the chamber is provided with the light emitting members 25 which emit horizontal light beams propagating through the chamber 21. Half-mirrors 32 are respectively provided in the vicinity of the supporting points of the floating floor 24 suspended by the electromagnetic actuators 2. Accordingly, the light beam emitted from each light emitting member 25 irradiates a corresponding half-mirror 32 and a part of the light beam is reflected thereby and received by the photosensor 26 of a corresponding electromagnetic actuator 2. Such being the case, horizontal light beams indicating a reference position are incident on the actuators 2 which suspend the floating floor 24 and positions of respective points on the floating floor 24 are detected relative to the reference position. As described heretofore, an electromagnetically suspended floating floor apparatus of the present invention maintains the floating floor 24 in a horizontal position with reference to horizontal light beams by controlling electromagnetic actuators. Therefore, the floating floor 24 is kept without fail in a horizontal position and is spacially separated from beams and pillars of a building whereby no vibration of the building is transmitted to the floor 24. Vibration generated at any part of the floating floor can be quickly attenuated by a control system. Accordingly, equipment to which no vibration is to be transmitted can be arranged freely on the floating floor and rearrangement of such equipment may be conducted easily.

Claims: An electromagnetically suspended floating floor apparatus having a floating floor (24) which is suspended from an installation floor (6) at a plurality of supporting points (31) by electromagnetic actuators (2), said floating floor (24) apparatus characterized by a combination of: light emitting means (25) provided at a member associated with said installation floor (6) to emit a horizontal light beam; photosensor means (26) fixed to said floating floor (24) to receive the horizontal light beam from said light emitting means (25) so as to supply to said electromagnetic actuators (2) a position signal representing a change in position of said floating floor (24); and means (9,10) for controlling a drive current flowing through said electromagnetic actuators (2), in accordance with the position signal in order to compensate the change in position of said floating floor (24). The floating floor apparatus according to claim 1, wherein a half-mirror (32) is provided in the vicinity of said supporting point such that the light beam emitted from said light emitting means (25) is directed to said photosensor means (26) by said half-mirrors. The floating floor apparatus according to claim 1, wherein said floating floor (24) and said installation floor (6) are respectively provided with acceleration sensors (29,30) output signals of which are applied to said actuators whereby partial vibration generated at said floating floor may be suppressed by said actuators.

Inventors: KANEMITSU YOICHI, WATANABE KATSUHIDE, YANO KENICHI, KANEMITSU, YOICHI, WATANABE, KATSUHIDE, YANO, KENICHI
Applicants: EBARA CORP, KAJIMA CORP, EBARA CORPORATION, KAJIMA CORPORATION
Application year: 1993
Main classification: F16F15
IPC codes: F16F15, E04F15