This paper deals with synthesis of structured controllers to make
fully use of information such as structures and/or characteristics
possessed by plants to be controlled and/or given by control
specifications. Such information is crucial to achieve successful
control results.

We first point out, through a speed control problem of ultrasonic
motors, that, even if robust control applied to a generalized plant
leads to a successful result, gain scheduled techniques applied to the
same generalized plant do not necessarily yield successful results.
In other words, problem formulations suitable for robust control are
not necessarily suitable for gain scheduled techniques. Based on this
fact, we propose problem formulations suitable for gain scheduled
techniques and provide the solutions. The proposed method yields a
controller which has a structure such as LPV or LFT. Moreover, the
structure is based on the information associated with control
specifications and plants. The effectiveness of the proposed method is
examined by experimental results of ultrasonic motor control.

On the other hand, structured controllers are advantageous also in
terms of implementations, since the structures are available to reduce
the complexity without any approximations such as controller order
reductions. Hence, we further propose a method to synthesize a
structured controller whose structure is led by that in the generalized
plants and yields easy implementation.