Marine Autopilot System Including Mode Engagement Features

Abstract

A marine autopilot system for ships in which the set course signal and the eading signal are supplied to a comparator which feeds a servomotor through an operational device to control the ship. In the present invention when the marine autopilot is automatically changing course, switching means change various constants and functions of the marine autopilot system and disconnect other elements which are unnecessary during course change.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automatic steering system, and more particularly to a marine autopilot system.

2. Description of the Prior Art

Generally, an automatic steering system has two principal functions. One is to hold a ship on a straight line along her set course. This function is required for long-distance navigation. The second function is to automatically change the ship's course. There are many occasions when the set course must be changed as for selecting the great circle route to a destination, for avoiding a collision with other ships, and for various other reasons. During an automatic course change, the ship should be steered to the newly set course without over-shoot, with the minimum number of steering operations and with minimum speed loss as quickly as possible.

Theoretically, holding a straight course is a steady response and a course change is a transient response.

Prior art autopilots have been designed and adjusted so as to enhance the course-keeping capability. In recent years, however, the size and speed of ships have increased and, as a result, the response of the ship to movement of the rudder exceeds the limits of manual steering operation. Therefore, in such ships it is almost impossible to employ conventional methods for changing course with manual steering operations and thus after the ship has been brought roughly to the set course, the manual steering operation is switched to automatic operation. For this reason automatic change of course has become of great interest. Further, a smaller number of operators are available due to the use of automatic navigation equipment and persons with little manual steering experience will often be utilized to do the steering operation, thus making course changes by automatic means more and more important.

Under limited conditions, in order that the transient and steady-state responses of an automatic control system be operated at optimum values, it is necessary to change the parameters of the control loop. The limited conditions herein mentioned result from the physical characteristics of the ship. For example, factors such as the rudder angle, the limit of the rudder angle and/or an upper limit of speed of the rudder movement. Also these conditions include problems of performance such as, for example, if the rudder is held at large angles very often for maintaining the ship on the set course, her sailing speed will be decreased due to drag on the ship. Also, frictional components of the steering gear would be rapidly worn out.

SUMMARY OF THE INVENTION

The performance of the marine autopilot system can be enhanced, if optimum response is obtained by the use of optimum parameters during course changes and while maintaining a fixed course.

Accordingly, one object of this invention is to provide a marine autopilot system which gives high performance.

Another object of this invention is to provide a marine autopilot system which allows the control parameters to be switched to different values which optimum for changing course or maintaining a fixed course.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram, for explaining a conventional autopilot system;

FIG. 2 is a schematic diagram showing one example of a marine autopilot system of this invention;

FIG. 3 is a schematic diagram illustrating one example of a means for driving the principal part of the system of this invention exemplified in FIG. 2;

FIG. 4A is a connection diagram showing one concrete example of the part depicted in FIG. 3;

FIG. 4B is a schematic diagram showing a modification of one part of the connection diagram depicted in FIG. 4A; and

FIGS. 5 and 6 are schematic diagrams illustrating other examples of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For a better understanding of this invention a detailed description will be given first of the construction and function of a conventional marine automatic steering system with reference to FIG. 1. A heading signal .phi. of a ship 12 or the like derived from a compass 13 mounted thereon is supplied to an adder 1 and is compared with a set course signal .phi.i fed to the adder 1. In the event that a deviation exists between the heading signal .phi. of the ship 12 and her set course signal .phi.i, the adder 1 converts the deviation into an error signal .phi.e and the resulting error signal .phi.e is supplied to a weather adjustment device or unit 2. In the illustrated example the weather adjustment device 2 is in the form of a dead-zone circuit, which may be replaced with a filter or an attenuator. The weather adjustment device 2 serves to avoid over use of the helm which results from an increase in the number of steering operations caused by yawing of the ship under the influence of external disturbances in bad weather conditions. The error signal .phi.e is applied to an integrator 3, a proportional amplifier 4 and a differentiator 5 connected in parallel and the resulting signals are combined together at an adder 6.

As is well-known, the autopilot controls the steering gear with the use of a rate signal K.phi.e proportional to the turning speed of the ship in addition to the signal K.phi.e proportional to the deviation between the actual ship's heading and the set course so as to stabilize a control loop including the ship. In some cases, the autopilot employs an integration signal in the control loop including the ship for controlling the steering gear with an integrated signal K.intg..phi.e together with the error and error rate signals in order to maintain the ship's heading on the set course .phi.i.

The operational signal K(.intg..phi.e + .phi. e + .phi. e) thus obtained is applied as the command signal to a motor 9. This signal is first fed through a rudder angle limiting control mechanism 16, an adder 7 and an amplifier 8 before reaching motor 9. The motor 9 actuates a rudder 14 through a gear mechanism 10. A feedback signal generator 11 is controlled by rotation of the output shaft of the motor 9 and produces a signal proportional to the steering angle. This signal is fed back to the input of the amplifier 8. Thus, the rudder 14 is driven to correspond to the operational signal in a minor control loop comprising the adder 7, the amplifier 8, the motor 9, the gear mechanism 10 and the signal generator 11.

Generally, the maximum angle of the rudder is limited by its mechanical construction but some rudders are provided with a mechanism which allows the rudder movement to be limited to an angle smaller than the maximum angle during automatic steering so as to increase safety. Such rudder angle control mechanism has response so as to be insensitive to normal rudder angles selected under normal steering conditions and prevents the rudder from suddenly being turned to the maximum angle causing sudden turning of the ship when the autopilot goes out of order.

It is the practice in the art to incorporate in the autopilot an alarm device or unit 15 including a buzzer or the like which raises an alarm when the ship's heading has deviated from its set course by a predetermined value. The alarm is given upon occurrence of the predetermined deviation between the ship's heading and the set course, so that during automatic course changes the alarm device continues to raise the alarm until the ship's heading approaches the newly set course. The alarm device is provided with a switch to prevent it from sounding during course changes of this type.

The problem is to bring the ship's heading to the newly set course without over-shoot and in the shortest possible time during an automatic course change which is a transient condition of the automatic steering system. Ideally different operational parameters in the operational device should be selected during course changes and course keeping. This would assure that autopilot characteristics detrimental to course changes would be removed during automatic course changes.

FIG. 2 illustrates one example of an automatic steering system of this invention provided with switch means for changing the autopilot parameters during course changes. In FIG. 2 similar reference numerals to those in FIG. 2 indicate similar elements which are identical in construction and in operation, and hence will not be described in detail for the sake of brevity.

In the figure those portions indicated by heavy lines are added to the conventional autopilot system according to this invention. In the illustrated example switches with contacts M.sub.1 to M.sub.4 are provided for respectively short-circuiting the weather adjustment device 2, the integrator 3, the differentiator 5 and the rudder angle limiting control mechanism 16. In addition, a switch with contact B is provided between the alarm device 15 and the output side of the adder 1.

The switch contact M.sub.1 short-circuits the weather adjustment circuit 2. A slight increase in the number of steering operations is insignificant for the short time required for changing the course of the ship. Disconnecting the weather adjustment circuit 2 allows the ship to turn to the newly set course with accuracy. The contact M.sub.1 is of particular utility when used with a dead-zone type weather adjustment circuit.

The switch contact M.sub.2 resets the integrator 3. In the example of FIG. 2 the integrator 3 is made up of an operational amplifier 3.sub.1 and a feedback capacitor 3.sub.2, so that the output of the integrator 3 is reset by short-circuiting the integrated charge on the capacitor 3.sub.2 with the contact M.sub.2. When the ship has changed her course, the influence exerted upon the ship by the turning torque due to fixed external disturbances such as winds and so on sometimes will be opposite in direction to those before the course change. The switch contact M.sub.2 allows the integrated output of the former course of the ship to be reset and an integrating operation of the newly set course is carried out.

The switch contact M.sub.3 is employed for changing the rate time constant of the differentiator 5. In the example of FIG. 2 a differentiating capacitor 5.sub.2 of the differentiator 5 is connected in parallel with a conventional differentiating capacitor 5.sub.4 when the contact M.sub.3 is closed during course change. The differentiating capacitor 5.sub.2 is inserted into the differentiator 5 to increase the rate time constant. Reference numeral 5.sub.1 indicates an operational amplifier of the differentiator 5. During an automatic course change it is necessary that sufficient meeting rudder be applied for cancelling the great turning inertia of the ship and this is provided by a longer rate time than that for usual course keeping. This diminishes the amount of over-shoot and enables the ship to conform with a newly set course in the shortest time.

The switch contact M.sub.4 short-circuits the rudder angle control circuit 16 for removing the small rudder angle limit. For changing the course a large rudder angle is required, as compared with the rudder angle for usual maintenance of the course and the control function of the rudder must be used fully for bring the ship to the newly set course within a short time. The rudder angle limiting control mechanism must be removed to obtain rapid course changes.

The switch contact B serves to disconnect of the alarm device 15 temporarily. Since the alarm device 15 operates from the heading deviation signal .phi.e during course changes, it would raise an alarm for every change of the course if not disconnected. It is desired to automatically reset the alarm device 15 while the course is being changed.

Further, the function of the autopilot can be enhanced by the provision of a contact device for holding various accessory circuits of the autopilot inoperative during the course change, though not shown in the example of FIG. 2.

Referring now to FIG. 3, a description will be given of one example of a device for controlling the switch contacts M.sub.1 to M.sub.4 and B of FIG. 2.

In FIG. 3 reference numeral 21 indicates a heading signal generating synchro incorporated in gyrocompass mounted on the ship. The output of the synchro 21 is supplied to a receiving synchro 22 in an autopilot. The synchro 22 is supplied with the heading signal .phi. of the ship. A deviation between the heading signal .phi. and a set course signal .phi.i occurs in differential gear 28 and is converted by a synchro 23 into a deviation signal .phi.e'. The resulting deviation signal .phi.e' is converted by a differential modulator 25 into a DC signal .phi.e, which is fed to an electric circuit 30 of the autopilot.

A course setting knob 24 of the autopilot is usually constructed so that it supplies an input through a clutch so as to avoid accidental changes which might occur if the operator should touch the knob. If a course is desired, the knob 24 is pressed to couple clutch members 27 and turned to rotate the differential gear 28. The knob 24 is always pressed upwardly by a spring 29 mounted between a stand 31 and the knob so that when the knob 24 is released after setting the course, the clutch members 27 disengage. At this time a contact of a micro switch 26 produces a pulse which represents that the ship has completed her course change. Since the time for closing the micro switch 26 for the course change may vary, the pulse signal derived from the micro switch 26 is applied through a memory circuit 32 to a timer 33 to actuate it. After a predetermined set time the timer 33 produces a reset signal to reset the memory circuit 32. The output of the memory circuit 32 is applied to a relay or a semiconductor switch 34 to drive it. The signal .phi.e is supplied through an amplifier 35 to a time setting variable resistor 33.sub.1 of the timer 33. This circuit is optional to this invention but performs the following operation to enhance the effect of the present system.

Within a range where the output .phi.e' of the synchro 23 remains unsaturated, the deviation signal .phi.e is proportional to the course changing angle. The time required for changing the course of the ship also increases with an increase in the course changing angle. Accordingly, by automatically changing the set time of the timer 33 in accordance with the signal .phi.e, the relay can be held operative for a certain period of time required for changing the ship's course.

FIG. 4A shows one example of the circuit construction of the system exemplified in FIG. 3. In FIG. 4 elements similar to those in FIG. 3 are identified by similar reference numerals for convenience of illustration. When the ship has changed her course, the micro switch 26 is closed to trigger the memory circuit 32 which may be a flip-flop circuit or a bistable multivibrator circuit. The output of the memory circuit 32 is supplied to the relay device 34 to actuate it. Respective contacts 34.sub.1, 34.sub.2, 34.sub.3, . . . . . of the relay device 34 constitute switching units for the respective circuits in such a manner that the autopilot will respond well during the course change. One portion of the output of the memory circuit 32 is applied through a variable resistor R.sub.3 and a resistor R.sub.4 to an integrating amplifier 36.sub.1 of the integrator 36. A diode D.sub.5 having a breakover point and a resistor R.sub.5 are connected as the load of integrator 36. The diode D.sub.5 may be a Shockley diode, SCR, SVS, UJT, or the like which permits the passage therethrough of a current when a voltage fed to it exceeds its breakover voltage. When the output voltage of the integrator 36 goes above the breakover voltage of the diode D.sub.5, a voltage is produced across the resistor R.sub.5 which is connected between the diode D.sub.5 and ground and this voltage is applied as a reset signal to the memory circuit 32 to reset it. The variable resistor R.sub.3 connected between the output end of the memory circuit 32 and the input end of the integrator 36 controls the integrator by altering its integrating time constant, thereby adjusting the operating time of the relay device 34. This allows adjustment to comply with the turning time which depends on the size and type of the ship and this adjustment is made depending on the size and type of the ship in which the equipment is mounted.

A transistor Q.sub.2 is operated by the signal .phi.e from an input terminal 37. The input signal to the integrator 36 is adjusted by a change in the internal impedance of the transistor Q.sub.2 between its collector C.sub.2 and emitter E.sub.2. Since the signal .phi.e is a bipolar signal whose polarity varies with the direction of the deviation, the input signal .phi.e is converted to one polarity by an inverter circuit 38 having a diode D.sub.2 and connected between the input terminal 37 and the base B.sub.2 of the transistor Q.sub.2. Thus, when the signal .phi.e is positive it flows into the base B.sub.2 of the transistor Q.sub.2 through a resistor R.sub.1 and a diode D.sub.1 which are inserted between the input terminal 37 and the base B.sub.2 of the transistor Q.sub.2 to lower the impedance of the transistor Q.sub.2 between the collector C.sub.2 and the emitter E.sub.2. At the same time one portion of the input to the integrator 36 from the memory circuit 32 is by-passed to ground through a diode D.sub.4 and the collector C.sub.2 and the emitter E.sub.2 of the transistor Q.sub.2. When the signal .phi.e is negative it is supplied through the resistor R.sub.1 to the inverter circuit 38 and is thereby reversed in polarity becomes a positive signal, which is applied through the diode D.sub.2 to the base B.sub.2 of the transistor Q.sub.2 to alter its impedance between its emitter E.sub.2 and collector C.sub.2, thereby changing the input to the integrator 36.

FIG. 4B is identical in construction with FIG. 4A except it uses a semiconductor switch as a substitute for the relay device 34. In the case where the respective contacts of the relay device 34 are required to be insulated from one another, a circuit such as shown in FIG. 4B is preferred. In the example of FIG. 4B the switch contacts M.sub.1 and M.sub.2 for short-circuiting the weather adjustment device 2 and the integrator 3 are respectively replaced by insulated-gate field effect transistors MOS.sub.1 and MOS.sub.2 and the output of the memory circuit 32 is applied to the gates MOS.sub.1G and MOS.sub.2G of the transistors MOS.sub.1 and MOS.sub.2 respectively. The weather adjustment device 2 and the integrating capacitor 3.sub.2 of the integrator 3 are respectively respectively interposed between the source MOS.sub.1S and drain MOS.sub.1D of the transistor MOS.sub.1 and between the source MOS.sub.2S and drain MOS.sub.2D of the transistor MOS.sub.2. With such an arrangement, when the output of the memory circuit 32 is applied to the gates MOS.sub.1G and MOS.sub.2G of the transistors MOS.sub.1 and MOS.sub.2, the weather adjustment device 2 and the integrator 3 are respectively short-circuited by the transistors MOS.sub.1 and MOS.sub.2 which are rendered conductive and when the input to their gates is removed the shorting circuits are cut off. Accordingly, these transistors MOS.sub.1 and MOS.sub.2 perform exactly the same function as the relay device 34 of FIG. 4A. Although the example of FIG. 4B has been described in connection with the case where only the switch contacts M.sub.1 and M.sub.2 of the relay device 34 of FIG. 4A depicted in FIG. 2 are replaced with the insulated-gate field effect transistors, it will be understood that the switch contacts M.sub.3, M.sub.4 and B may have insulated-gate field effect transistors substituted for them.

In the event that the circuits such as the weather adjustment device and so on to be short-circuited need not be insulated from one another, conventional transistor switching circuits may be used.

FIG. 5 illustrates a modified form of this invention, in which reference numerals similar to those in FIG. 3 indicate similar elements. In the present example the deviation signal .phi.e is used as a trigger signal representing a course change. The output .phi.e' of the synchro 23 is applied to a demodulator 25, whose output signal .phi.e is fed to a comparator 45. The comparator 45 produces an output when the input signal .phi.e exceeds a certain set value. The output of the comparator 45 is applied to the memory circuit 32 to trigger it, causing the circuit 32 to start the timer 33 and driving the semiconductor switching device or the relay device 34. Also, the output of the timer 33 is fed back to the memory circuit 32 as a reset signal. The system shown in FIG. 5 is advantageous in that it can be triggerred in a pure electronic manner.

FIG. 6 shows another modification of this invention, in which reference numerals similar to those in FIG. 5 designate similar elements. This example is simpler in construction than that of FIG. 5 in that the signal .phi.e from the demodulator 25 is applied to the comparator 45 to control its set level only and the relay device 34 is directly driven by the output of the comparator 45.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.

Claims

We claim as our invention:

1. A marine autopilot system for a ship for operating in a fixed course holding mode and a turn to a new course mode comprising:

a servo motor connected to the rudder of said ship to control it;

a course setting knob;

means for producing an error signal corresponding to the deviation between a set course and the ship's heading and set course setting knob connected thereto;

an operational means connected between said servo motor and said means for producing an error signal and including a weather adjustment device;

an integrator, a differentiator and a rudder angle limit means;

a first switch mounted adjacent said course setting knob and actuated thereby when said course setting knob is operated to set a new course;

a memory device connected to said first switch and producing an output each time said first switch is actuated for a time period until said memory is reset;

a variable timer receiving an input from said memory and supplying a delayed output to said memory to reset it, said means for producing an error signal supplying an input to said variable timer to control the delay between the timer's input and output;

a second switch connected in parallel with said weather adjusting device;

a third switch connected to said integrator for disconnecting it;

a fourth switch connected to said differentiator for changing the response; and

switch actuating means receiving an input from said memory and connected to actuate said second through fourth switches such that during a turn to new course mode said weather adjusting device and integrator are disconnected, and said differentiator has a different response than during said course holding mode.

2. A marine autopilot according to claim 1 further including:

a fifth switch with one side connected to said means for producing an error signal; and

an alarm connected to the other side of said fifth switch, and said switch actuating means connected to open said switch during turn to new course mode.

3. A marine autopilot according to claim 2 further including:

a rudder angle limiting means forming a part of said operational means; and

a sixth switch connected in parallel with said rudder angle limiting means and said switch actuating means connected to close said sixth switch during turn to new course mode.

4. A marine autopilot according to claim 1 wherein said second and third switches are field effect transistors.