Patent ID: 7768225

Claim:
A servo control system for a steerable mirror secured on a drive shaft of a rotary actuator, said servo control system being provided with a feedback loop such that said steerable mirror is positioned in an angular position based on position command data, comprising: an input means for inputting an input signal which is said position command data; and an additional input means for inputting at least one additional input signal, which is other than said position command data, to said feedback loop, wherein said additional input means is designated to add zeros to a transfer function for a q-th initial state value x p 0 q so as to cancel out poles of said transfer function, which poles are inherent in said feedback loop, in said transfer function for said initial state value x p 0 g of said feedback loop at a time at which said position command data has been received, wherein said zeros are roots of the equation N pq (z)d q (z)+N u (z)n q (z)=0, where N pq (z) is the q-th element of the 1×m high-order polynomial matrix (1≦q≦m) of the transfer function of said feedback loop, d q (z) is the denominator of the transfer function of a digital filter for the q-th initial state value x x0q , N u (z) is the numerator of the transfer function for said additional input means, n q (z) is the numerator of the transfer function of said digital filter for the q-th initial state value X p0q , and wherein said poles are roots of the equation D(z)=0, where D(z) is the denominator of the transfer function of said feedback loop, which poles are relating to the first-order torsional vibration mode of said drive shaft.