Figure 1 and figure 2 bellow show the VAAV response displacement and rotation vibration of the board, caused by a stage movement.

• Fig.1 A sample of rotation displacement response
• Fig.2 A sample of rotation vibration response

There are two types of actions caused by stage load movements.

The first is the revolving moment which is proportional to the product of stage mass and stage displacement.
And the second is the driving force which is proportional to the product of stage mass and stage acceleration.

If the mass, the displacement, and the acceleration are big, they generate large response.
In the case of soft passive support control, the response displacement sometimes becomes too large to exceed the tolerable level of air spring. Feed-back control, (FB control) using active anti-vibration makes the vibration amplitude small and settle in short time. For this reason, precise positioning and reduction of settling time can be realized with active anti-vibration control. (Fig. 1 and Fig. 2)

Moreover, SFF (stage feed forward) control can be executed by connecting analogue signal of stage displacement data to VAAV controller.

Figure 1 shows how response displacement caused by a stage movement cancelled by SFF control becomes small (refer Fig. 1).

VAAV SFF control is theoretically simple and reasonable. So, big effect can be easily achieved (PAT). SFF control up to two axes can be executed.

Samples of the stage displacement and stage acceleration real time signal are shown in figure 3 and 4.

Please prepare analogue signal having ±10V range. It is necessary that the earth voltage of your signal generator is equal to that of VAAV controller.

Fig. 3: A sample of stage displacement signal

Fig. 4: A sample of stage acceleration signal