[Ushiba, Miyamoto, Hasegawa, Enomoto, Nagano, Okutomi (remote)]

We tried to return main beam to the BS but we couldn't.

**********Method**********
We set the small slit (~10mm in diameter) 0.5m away from the HR surface of the ETMY.
We tried to return the beam that came through this slit to the same slit for rough alignment of the ETMY.
Pitch control is performed by the stepper motor on the Marionette stage.
Yaw ontrol is done by the picomotor on the Bottom Filter stage.

**********Problem**********
Yaw motion cannot be controled precisely by the picomotor.
If we move the picomotor for a short time (less than ~20 second), there is almost no change of the yaw angle.
If we move the picomotor for a long time (over ~20 seconds), we can change the angle.
But onece the mirror moves, mirror angle changes over 5mrad (too big!!).
So, we cannot control the mirror angle precisely and return the beam back to the slit.

**********trial and error**********
We tried to  control the yaw angle by using the BF LVDT first.
But since the dinamic range of the LVDT is small (less than 1mrad), we couldn't conpensate the yaw misalign (~ several mrad).

We consider that this uncontrolable actuator motion is caused by the friction between suspension point and bearings.
So, we tried to give a shock to the Bottom Filter by using the actuators on the BF and release the stress of the bearings.
But this trial was not succeeded and the angle didn't change after giving the shocks.