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Vibration cancellation apparatus

  • US 5,876,012 A
  • Filed: 06/23/1997
  • Issued: 03/02/1999
  • Est. Priority Date: 06/21/1996
  • Status: Expired due to Fees
First Claim
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1. A vibration cancellation apparatus for isolating an anti-vibration table from floor vibration and for canceling vibration of an objective equipment on the anti-vibration table which produces a load on the anti-vibration table, said apparatus comprising:

  • at least three electromagnetic actuators operable to support and move the anti-vibration table;

    at least three displacement sensors, each in a respective electromagnetic actuator, each operable to detect a vertical position of the anti-vibration table to output a displacement signal indicative of the vertical position of the anti-vibration table, wherein the vertical position in each of the displacement sensors changes in response to a change in the load of the objective equipment which corresponds to a movement of a center of gravity of the anti-vibration table caused by movement of the objective equipment on the anti-vibration table;

    at least three acceleration sensors, to be connected to the anti-vibration table, each operable to detect vertical accelerations of the anti-vibration table at the respective acceleration sensor and to output an acceleration signal indicative of the vertical accelerations at the respective acceleration sensor;

    a first compensation circuit for generating first compensation signals corresponding to the displacement signals from said displacement sensors, respectively;

    a second compensation circuit for generating corresponding second compensation signals based on the acceleration signal from said acceleration sensors, respectively;

    levitation position control means for controlling said electromagnetic actuators based on the first compensation signals;

    vibration canceling control means for controlling said electromagnetic actuators based on the second compensation signals;

    air spring actuators to be placed in contact with the anti-vibration table and operable to support and move the anti-vibration table by air pressure in said air springs, said air spring actuators operable for supporting four corners of said anti-vibration table by air pressure, said air pressure of each air spring actuator being independently adjustable by air pressure control means respectively, said air in each of said air spring actuator being controlled in response to a change of load weight which corresponds to a movement of gravity caused by movement of said objective equipment on said anti-vibration table; and

    a control output distributor for receiving the first compensation signals from said first compensation circuit and for converting the first compensation signals to respective air pressure signals;

    whereby said movement of said objective equipment on said anti-vibration table causes output signals from said first compensation circuit based on said movement of said objective equipment, and said output signals from said first compensation circuit are supplied to control output distributor and converted to air pressure signals to each of said air spring pressure control means therein.

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