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

• Current Assignee: Ebara Corporation
• Original Assignee: Ebara Corporation
• Inventors: Haga, Takahide, Watanabe, Katsuhide
• Primary Examiner(s): Ramirez, Ramon O.
• Assistant Examiner(s): LIPCSIK, ROBERT N
• Application Number:
  US08/880,640
• Time in Patent Office: 617 Days
• Field of Search: 248/550, 248/636, 248/638, 248/562, 188/267, 188/378, 188/136
• US Class Current: 248/550
• CPC Class Codes: F16F 15/02 Suppression of vibrations of non-rotating, e.g. reciprocating systems; Suppression of vibrations of rotating systems by use of members not moving with the rotating systems F16F15/005 takes precedence ; layered products B32B; suppression of vibration in ships B63; relieving load on bearings, using magnetic means F16C39/06
• CPC Class Codes: F16F 15/0275 Control of stiffness

Abstract

A compact vibration cancellation apparatus based on a combination of air springs and electromagnetic actuators with smaller power capacity enables an anti-vibration table to be maintained in a level position even when the center of gravity of the anti-vibration table moves a large distance because of a movement of objective equipment on the table. The vibration cancellation apparatus is operable for isolating floor vibration or for canceling vibration of the objective equipment on the anti-vibration table. The apparatus includes displacement sensors, acceleration sensors, a levitation position control device, a vibration canceling control device, and air spring actuators for supporting four corners of the anti-vibration table by air pressure. The air pressure in each air spring actuator is controlled in response to a change of load which corresponds to a movement of the center of gravity caused by movement of the objective equipment on the anti-vibration table.

Claims

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.

2. A vibration cancellation apparatus as claimed in claim 1, wherein said acceleration sensors are each installed at a different location than said electromagnetic actuators, said vibration cancellation apparatus further comprising:

an acceleration point transformation device for converting the acceleration signals from said acceleration sensors indicative of the vertical accelerations at the respective acceleration sensors into equivalent action-point signals indicative of vertical accelerations at the electromagnetic actuators.

3. A vibration cancellation apparatus as claimed in claim 1, wherein said first compensation circuit is operable for producing output signals so as to keep the anti-vibration table to be levitated at a target value.

4. A vibration cancellation apparatus as claimed in claim 1, wherein said second compensation circuit is operable for producing output signals so as to reduce vibrations of the anti-vibration table.

5. 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 at the respective electromagnetic actuator and to output a displacement signal indicative of the vertical position of the anti-vibration table at the respective electromagnetic actuator, wherein the vertical position in each of the displacement sensors changes in response to a change in the load of the objective equipment at the respective electromagnetic actuator 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 signals 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 the anti-vibration table by air pressure in said air springs;

a location controller for controlling movement of the objective equipment and for outputting location signals indicative of the movement of the objective equipment controlled by said location controller;

a feedforward controller for converting the location signals from said location controller to equivalent air pressure signals; and

air pressure control means for receiving the air pressure signals from said feedforward controller and for controlling the air pressure in each of said air springs independently based on the air pressure signals.

6. A vibration cancellation apparatus as claimed in claim 5, wherein said acceleration sensors are each installed at a different location than said electromagnetic actuators, said vibration cancellation apparatus further comprising:

an acceleration point transformation device for converting the acceleration signals from said acceleration sensors indicative of the vertical accelerations at the respective acceleration sensors into equivalent action-point signals indicative of vertical accelerations at the electromagnetic actuators.

7. A vibration cancellation apparatus as claimed in claim 5, wherein said first compensation circuit is operable for producing output signals so as to keep the anti-vibration table to be levitated at a target value.

8. A vibration cancellation apparatus as claimed in claim 5, wherein said second compensation circuit is operable for producing output signals so as to reduce vibrations of the anti-vibration table.