Servo controller design based on frequency-dependent error

Variables to be controlled are usually taken from measured outputs. They may be filtered and the regulation of frequency-dependent error has been considered in the design of robust controllers. Anderson considered the frequency-dependent linear-quadratic (LQ) problem. The frequency-dependent weight he considered is restricted to the phase lag and lead type. This paper considers not only regulation of general frequency-dependent errors but also a servo controller tracking to a given reference signal in the presence of disturbances. The control law is determined either on the basis of the quadratic criterion function or by pole assignment in a region. The control law to assign poles in a region is derived from one designed for the corresponding discrete-time system obtained by bilinear transformation.