Patent ID: 8805556

Claim:
An assembly comprising: a stage apparatus that includes a first stage, a second stage, a first motor that moves the first stage and the second stage along an X axis, and a second motor that moves the second stage along a Y axis that is orthogonal to the X axis; a base plate that supports the stage apparatus; a first mount, a second mount, a third mount and a fourth mount that are spaced apart and that cooperate to support the base plate in a vertical direction; and a control system that controls the first, second, third, and fourth mounts, the control system includes a thrust calculating unit that utilizes an equation as provided below to calculate at least a portion of a thrust value for the first mount: F A = W 4 - W 2 ⁢ L X ⁢ X - W Y 2 ⁢ L Y ⁢ Y + W Y L X ⁢ L Y ⁢ XY where (i) F A is a thrust value for the first mount; (ii) W is a force that the first stage and the second stage exert upon the base plate as a result of gravity; (iii) W Y is a force that the second stage alone exerts on the base plate as a result of gravity; (iv) X is a position of a center of gravity of the second stage along the X axis, (v) Y is a position of the center of gravity of the second stage along the Y axis, (vii) L X is a distance between the first mount and the second mount in an X direction, and (viii) L Y is a distance between the first mount and the third mount in a Y direction.