Autopilot

Fig. 1.13 Block diagram of ship autopilot control system.

A control system may have several feedback control loops. For example, with a ship autopilot, the rudder-angle control loop is termed the minor loop, whereas the heading control loop is referred to as the major loop. When analysing multiple loop systems, the minor loops are considered first, until the system is reduced to a single overall closed-loop transfer function. 

Control action In this ease, the autopilot (eontroller) is eonsidered to provide proportional eontrol only. 

Control problem For a speeifie hull, the eontrol problem is to determine the autopilot setting K ) to provide a satisfaetory transient response. In this ease, this will be when the damping ratio has a value of 0.5. Also to be determined are the rise time, settling time and pereentage overshoot. 

Fig. 4.38 Unit step response of ship autopilot control system. RiseTime (to 95%) = 23 seconds ...

From equations (3.58) and (3.59) the unit step response for the ship autopilot eontrol system is given by the expression... 

The decision on the type of performance index to be selected depends upon the nature of the control problem. Consider the design of an autopilot for a racing yacth. 

Conventionally, the autopilot is designed for course-keeping, that is to minimise the error ipeit) between that desired course ipdit) and the actual course tp (t) in the presence of disturbances (wind, waves and current). Since is fixed for most of the time, this is in essence a regulator problem. 

Using classical design techniques, the autopilot will be tuned to return the vessel on the desired course within the minimum transient period. With an optimal control strategy, a wider view is taken. The objective is to win the race, which means completing it in the shortest possible time. This in turn requires ... 

In Figure 10.30 the predietive neural network model traeks the ehanging dynamies of the plant. Following a suitable time delay, em(kT) is passed to the performanee index table. If this indieates poor performanee as a result of ehanged plant dynamies, the rulebase is adjusted aeeordingly. Riehter (2000) demonstrated that this teehnique eould improve and stabilize a SOFLC when applied to the autopilot of a small motorized surfaee vessel. 

Case study Example 4.6.3 is a ship autopilot eontrol system. The bloek diagram representation is given by Figure 4.37. Inserting system parameters gives a forward-path transfer funetion... 

Case study example 4.6.3 (Ship Autopilot Control System)... 

Polkinghorne, M.N. (1994) A Self-Organising Fuzzy Logic Autopilot for Small Vessels, PhD Thesis, School of Manufacturing, Materials and Mechanical Engineering, University of Plymouth, UK. 

Richter, R. (2000) A Predictive Fuzzy-Neural Autopilot for the Guidance of Small Motorised Marine Craft, PhD Thesis, Department of Mechanical and Marine Engineering, University of Plymouth, UK. 

Richter, R., Burns, R.S., Polkinghorne, M.N. and Nurse, P. (1997) A Predictive Ship Control using a Fuzzy-Neural Autopilot. In Eleventh Ship Control Systems Symposium, Southampton, UK, 14-18 April, 1, pp. 161-172. 

Sutton, R. and Jess, I.M. (1991) A Design Study of a Self-Organising Fuzzy Autopilot for Ship Control. In IMechE, Proc. Instn. Mech. Engrs., 205, pp. 35-47. 

Sutton, R. and Marsden, G.D. (1997) A Fuzzy Autopilot Optimized using a Genetic Algorithm, Journal of Navigation, 50(1), pp. 120-131. 

When a microscopic invader breaches the outer defenses of the body the immune system swings into action. This happens automatically. The molecular systems of the body, like the Star Wars anti-missile system that the military once planned, are robots designed to run on autopilot. Since the defense is automated, every step has to be accounted for by some mechanism. The first problem that the automated defense system has is how to recognize an invader. Bacterial cells have to be distinguished from blood cells viruses have to be distinguished from connective tissue. Unlike us, the immune system can t see, so it has to rely initially on something akin to a sense of touch. 

There is an old Chinese greeting, May you live in uninteresting times. Indeed, if life were unchanging and less challenging, we could slip into autopilot or cruise control. But the second century of chemical engineering will not be dull. We will have splendid opportunities to conquer new frontiers, but we will have to work hard to get there. See you at the frontiers ... 

Although the value of on-line constrained optimization is expUcitly identified in this passage, the concept of moving horizon is missing. That is, perhaps, due to the fact that the author was concerned with the design of autopilots for airplane landing, a task that has a finite duration T. The algorithm described above is, essentially, the mathematical equivalent of MFC for a batch chemical process. 

---