A consistent approach to the development of tuning rules for course-keeping and path-tracking PID controllers for a ship autopilot are presented. The consistency comes from the observation that for each of the controllers the controlled plant can be modelled by an integrator with inertia. In the case of the course controller, it is the well-known Nomoto model. The PID controller may be implemented in series or parallel form, the consequence of which is a 2^nd or 3^rd order of the system, specified by a double or triple closed-loop time constant. The new tuning rules may be an alternative to the standard ones given in [1,2]. It is shown that, whereas the reference responses for the standard and new rules are almost the same, the new rules provide better suppression of disturbances such as wind, waves or current. The parallel controller is particularly advantageous. The path-tracking PID controller can provide better tracking accuracy than the conventional PI. Simulated path-tracking trajectories generated by a cascade control system are presented. The novelty of this research is in the theory, specifically in the development of new tuning rules for the two PID autopilot controllers that improve disturbance suppression.

An extremum "on-off" controller whose detailed description is given here is designed to continuously operate an industrial process at the extreme value of the process output. The process investigated consists of the following in cascade: a pure time delay, a parabolic function, and a first-order lag. A simple method is presented for selection of the three controller parameters, a gain, a velocity constant, and a dead time. The gain and the velocity constant are chosen so as to obtain a desired average output for the oscillation cycle. The main advantages of the controller designed are speed in reaching the extremum and low sensitivity to disturbances (because of low value of gain). A step-by-step procedure for the control system design is given.