GB1595582A

GB1595582A - Speed indicating system

Info

Publication number: GB1595582A
Application number: GB2746/77A
Authority: GB
Original assignee: AGA NAVIGATION AIDS Ltd
Current assignee: AGA NAVIGATION AIDS Ltd
Priority date: 1977-01-24
Filing date: 1977-01-24
Publication date: 1981-08-12
Also published as: SE7800182L; FR2378284A1; DE2802516A1

Description

(54) A SPEED INDICATING SYSTEM (71) We, AGA NAVIGATION AIDS LIMITED, a British Company, of 77 High Street, Brentford, Middlesex. TW8 OAB, do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- The present invention relates to a speed indicating system for providing indication to the pilot of a moving ship of the ships adherence to a desired speed profile as the ship travels along a predetermined path as defined by a harbour entrance channel.

In order to assist a ship in negotiating a harbour entrance and an approach channel to a wharf or jetty, it has been previously proposed to use what is known as a single station leading light. This leading light projects a narrow central beam of light, usually white, along a required fixed course, and two narrow side beams are located one on either side of the central beam. The port and starboard beams are red and green respectively, and the light is arranged so that there is a sharp change from the central white beam to either of the side beams.

When the ship is directly on course, the pilot will see the white beam, and if the ship veers slightly off course then he will see either red or green, depending on the direction of deviation from course. If the ship veers further off course, then the pilot will see nothing.

It will be appreciated that the abovementioned leading light can indicate only a straight line course, and cannot assist the pilot in determining whether or not the ship is travelling at a required low speed along the approach channel.

With many harbour installations, before a ship can berth alongside a wharf or jetty it is usually necessary for the ship to negotiate the harbour entrance and then proceed along what may be a complicated approach channel to what is called a swinging region or ground just outside the jetty. When the ship has reached the swinging region, it has to swing round and continue decelerating so as to come alongside the jetty and remain stationary. This swinging and stopping operation is a complicated manoeuvre, and is dependent upon the ship approaching the swinging region in conformity with an accurately controlled preselected ground speed profile, and then swinging round at an accurately controlled preselected rate of swing profile.

In this Specification the term "ground speed" means the speed relative to the ground. It will be appreciated that the ground speed will differ from the speed relative to the water because the water is moving due to a current or running tide.

By "speed profile" is meant the incremental values of speeds and rates of change of speeds over a chosen time period or distance. Similarly, by "rate of swing profile" is meant the incremental values of rates of swing and rates of change of swing over a chosen time period or distance.

It will be appreciated that, particularly with very large ships such as the supertankers, any deviation from a preselected value of the approach ground speed profile and rate of swing profile can cause considerable error in handling the ship, and may lead to damage of the ship and the harbour installation.

In this Specification references to the term speed is intended to refer to ground speed.

It is an aim of the invention to provide a speed indicating system for providing indication to the pilot of a moving ship of the ship's adherence to a desired speed profile as the ship travels along a predetermined path as defined by a harbour entrance channel, said system comprising: a source of electromagnetic energy, means for transmitting a central beam of said energy, means for transmitting discrete side beams of energy adjacent said central beam, said discrete beams being at frequencies different from one another and from the central beam, means for rotating said central and discrete side beams together, and on a common axis at a shore based location to cause said beams to intercept said predetermined path at substantial angles, said means for rotating said beams including an electric pulse motor of the type having an output shaft capable of rotating through an angular displacement related to the number of electrical pulses in an input pulse train to the said motor and said motor shaft rotating at a speed related to the frequency of said pulses in said pulse train, and said pulse train having a frequency which is variable to reduce the speed of rotation of the beams from a maximum at the channel entrance to a minimum at the inner end of the channel where the ship must be further manoeuvred for docking or the like.

The beam may be composed of any suitable radiation such as for example visible light, infra red or ultra violet light, radio-frequency energy or a laser beam.

One embodiment of the invention wilt now be described by way of example with reference to the accompanying illustrative drawings in which: Figure I is a chart of an approach channel to a ship's jetty and Figure 2 is a block schematic diagram of one speed indicating system of the invention.

Referring to Figure 1, a continuous line extending between the points AA and FF indicates the final three miles of an approach channel 2 to a swinging region FF to ZZ immediately outside a jetty 4.

Although two shore lines are shown, it will be appreciated that there need only be one shore line from which the jetty 4 extends.

A first speed indicating system 6 of the invention is located on shore between 1.3 and 2 nautical miles from the approach channel 2 so as to be clearly visible from a ship at all points on the approach channel between AA and FF. An identical second speed indicating system 8 of the invention is also located on shore so as to be clearly visible from the ship at all points in the swinging region between FF and ZZ.

In operation, the system 6 picks up the approaching ship at the commencement of the approach channel 2 at the point AA.

The pilot has previously decelerated the ship so that it is steaming at approximately five knots when it reaches AA. The system 6 then operates in accordance with a preselected speed programme in a manner to be hereafter described to enable the pilot progressively to decelerate the ship so that it is travelling at four knots, three knots, two knots, and one knot respectively when it reaches the points BB, CC, DD and EE, and has slowed down to 0.25 knots when it reaches the start of the swinging region at the point FF.

The second system 8 then takes over to swing the ship through the positions 10,12, 14, 16, 18 and 20. As seen from the chart, the fore and aft axis of the ship rotates approximately 140 between the position 10 and 20, and the time taken to travel between these two positions is approximately thirty minutes. The system 8 is controlled so that in addition to swinging, the ship also continues decelerating to arrive at the position 20 substantially stationary so that the shore dopplers can take over when the ship is approximately 200 metres from the jetty 4. While the ship travels through the swinging region, the pilot is located at the stern of the ship and uses his gyro heading in combination with the system 8.In order to obtain an accurate rate of swing control of the ship it is necessary for the system 8 to be closer than the system 6 to the jetty area.

Referring to Figure 2, each speed indicating system 6 and 8, includes an optical projector 22 mounted on a turntable 24 which is rotatably driven by a pulse motor 26 via a gear train 28. The gear train 28 has a gear ratio of 9600:1 and in order to take up any backlash in the gears, the turntable 24 is spring loaded towards the starting or lockon position.

At the starting position there is a mechanical and/or electrical stop so that the projector beam is always pointing in precisely the same direction when the guidance system is ready to be operated; i.e.

the positions AA and FF of the systems 6 and 8.

The projector 22 projects a narrow central beam of white light, and two narrow side beans on either side of the central beam. The side beams on the port and starboard side are red and green respectively, and there is a sharp change from the central white beam to either of the side beams. The composite beam is formed by projecting the image of a slide divided vertically into three segments coloured red, white and green respectively. The composite beam is oscillated sideways at a constant speed either by moving the slide with respect to the projection optical system, or by moving the entire projection system relatively to the slowly rotating turntable 24. The slide or projection system is moved to oscillate the beam by means of a motor which is independent of the pulse motor 26. One example of a suitable projection beam is as follows:- Red sector 4" White sector 5 Green sector 40 Oscillation angle + and -2" Oscillation rate 1 per second.

The pulse motor 26 of the speed control system includes a permanent magnet rotor having twenty four poles. A pair of windings in quadrature coact with the rotor and if one winding is energised (the other winding being de-energised), then the rotor will advance one pole i.e. 1/24th of a revolution.

If the two windings are then switched over, the rotor will advance one further pole, and it will be seen that the rotor rotates in steps of one twenty fourth of a revolution by this switching over of the two windings.

If a train of pulses is supplied to the winding, the rotor will rotate in a series of steps, and speeds from zero up to several hundred revolutions per minute can be achieved. Provided that the rotor is not mechanically overloaded its speed of rotation will follow precisely the frequency of the applied pulses. For example, if a total of 2,400 pulses are applied in sequence to the motor, then the motor shaft will rotate exactly one hundred turns.

If the ship is travelling along the correct portion of the approach channel 2 at precisely the preselected desired speed, then the pilot will see the white beam only.

If the ship is slightly too fast or too slow, then the pilot will see either red and white flashes or green and white flashes. If the ship is further from its correct speed schedule then the pilot will see the red or green flashes, and if the ship's speed is even further from the required value then the pilot will not see the beam at all.

With the above example of a suitable projection system, the fixed white beam will be observed over a scanning range of plus or minus QO from the correct position, which means that the ship is at plus or minus 0.01 nautical miles from its correct position on the approach channel 2. A progressively changing red and white or green and white signal will be received for error angles between plus and minus 9" which corresponds to errors in the vessel's position of approximately plus and minus 0.25 nautical miles.

Referring to the chart of Figure 1, the required rotational speed of the projector 22 of the system 6 is calculated to ensure that the beam traverses the approach channel 2 in order to decelerate the ship to a speed of 0.25 knots at the point FF. Similarly, the rotational speed of the beam of the identical system 8 is calculated in order to swing the ship correctly between the positions FF and ZZ. These rotational speeds are dependent upon the speed profile for a particular sized ship, the location of the systems 6 and 8 in relation to the approach channel 2 and the jetty 4, and possibly also the preferences of different pilots. The rotational speed of each beam is calculated for progressively increasing time intervals from the start of the guiding operation when the ship reaches the point AA or FF respectively.

In operation, the system 6 is switched on automatically by remote control from an operations room as the vessel approaches the starting point AA of the approach channel 2. At this point, the projector 22 will be stationary, and the pilot informs the operation room by radio when the ship is in the centre of the white beam. The system 6 than commences to rotate the projector 22 in accordance with the pre-selected speed programme, and the pilot steers the ship along the approach channel 2 and maintains station with the white beam. In this way the ship is steadily decelerated until it reaches the point FF at a speed of 0.25 knots, at which point the system 6 is returned to its initial position with the beam directed at the point AA.The pilot master then informs the operations room when he can see the white beam from the system 8, whereupon the system 8 is rotated at the calculated speed from the position FF to the position ZZ.

The pilot positions himself in the rear of the vessel, and maintains station with the white beam in order to swing the vessel between the positions 10 and 20 and to bring the vessel to rest at position 20. When the vessel is in this position 20 the shore dopplers take over about 200 metres from the jetty 4. It takes approximately thirty minutes to swing the vessel between the positions 10 and 20, and the rate of swing is greatest through the positions 14 and 16.

In operation of each speed control system, the pulse motor 26 is actuated by a tape on which is recorded a pulse train corresponding to the desired speed profile of a particular ship and the approach channel 2.

In order to obtain the correct pulse train for the approach channel 2, a table is drawn up plotting the required rotational speed of the projector beam against the time period which has elapsed since the beam started rotating from the start position AA.

There is used a pulse generator in the form of a stable audio frequency oscillator which feeds 9 pulse shaping circuit to provide substantially square wave pulses for the windings of the pulse motor 26. The oscillator has a variable frequency output in the range from 1.9 HZ to 39 HZ corresponding to pulse motor speeds of 4.75 revolutions per minute to 97.5 revolutions per minute. With the aforementioned reduction of the gear system 28, this pulse frequency provides rotation speeds of the turntable 24 in the range of 0.178 to 3.650 per minute. The frequency of this oscillator is controlled by a precision potentiometer calibrated in degrees per minute. The playing time of the tape recorder is monitored by a stop watch which is preferably electronic with a digital read-out.

To record a pulse programme, a programmer starts the tape recorder and the stop watch and ten adjust the potentiometer continuously so that the indicated speed in degrees per minute corresponds exactly to the required degrees per minute reading on the chart corresponding to the time shown on the stop watch. The programmer periodically checks that the cumulative angle of rotation from the start position AA corresponds to the elapsed time from the commencement of rotation. This check is carried out by means of an electronic circuit which counts the pulses emitted by the pulse generator and divides by 26. This enables the circuit to provide a read out of the cumulative angle of rotation for every 0.1 rotation of the projector 22.When the pulse train for the complete approach channel 2 has been recorded, the tape recorded is switched off.

On using the tape to drive the pulse motor 26, the centre of the projector beam will follow precisely the required speed profile of a particular ship travelling along the approach channel 2.

In addition to the above described methods of obtaining a pulse programme, it is possible to use other programming methods using digital computer techniques.

One method using digital computer techniques involves using a programme store and a processor. The programme store consists of a set of pre-wired sockets into which individual programme units can be plugged. These programme units are conventional Electrically Programmable Read Only Memories which will be referred to as E-PROMS. Each E-PROM will contain several programmes, and can be programmed by the manufacturer in response to appropriate supplied data. It is proposed to provide sufficient space for storing 100 programmes.

The processor contains instructions for providing an output in response to the information fed to it from the programme store. The output from the processor is a series of pulses which is fed to the pulse motor 26 so as to rotate the projector 22 in accordance with the selected programme.

WHAT WE CLAIM IS: 1. A speed indicating system for providing indication to the pilot of a moving ship of the ship's adherence to a desired speed profile as the ship travels along a predetermined path as defined by a harbour entrance channel, said system comprising: a source of electromagnetic energy, means for transmitting a central beam of said energy, means for transmitting discrete side beams of energy adjacent said central beam, said discrete beams being at frequencies different from one another and from the central beam, means for rotating said central and discrete side beams together, and on a common axis at a shore based location to cause said beams to intercept said predetermined path at substantiai angles, said means for rotating said beams including an electric pulse motor of the type having an output shaft capable of rotating through an angular displacement related to the number of electrical pulses in an input pulse train to the said motor and said motor shaft rotating at a speed related to the frequency of said pulses in said pulse train, and said pulse traip having a frequency which is variable to reduce the speed of rotation of the beams from a maximum at the channel entrance to a minimum at the inner end of the channel where the ship must be further manoeuvred for docking or the like.

2. The system as claimed in Claim 1 wherein said input pulse train is selected from a collection of pulse trains of various predetermined frequency distributions each of which predetermined pulse trains represents a desired relationship between the angular rotation of displacement (0) of the beam with reference to an initial or "lock-on" position and the desired speed of the ship at several angular positions (AA BB, CC, DD, EE, FF), said speeds being reduced at said positions in proportion to stepped decreases in frequency for the pulses in the pulse train, and means for biassing said beam toward said initial angular position.

3. The system as claimed in Claim 1 or Claim 2 further characterised by said means for transmitting said beam of energy comprising a light projector with at least three distinct colours to permit visual distinctions between the central beam and the discrete side beams adjacent thereto, said means for rotating said three light beams comprising a turntable and gear reduction means between said pulse motor and said turntable.

4. The system as claimed in Claim 3 further characterised by means for laterally oscillating at least one of said light beams at a frequency such that said at least one beam is cyclically interrupted with respect to an observer on the ship, to create flashes of light rather than a steady beam.

5. A system as claimed in Claim 3 or Claim 4, including a slide to form said central and side beams.

6. A system as claimed in any preceding Claim, in which the beam transmitting means is mounted on a turntable.

7. A system as claimed in Claim 6, in which the turntable is biased towards a starting position.

8. A system as claimed in Claim 6 or Claim 7, in which the electric pulse motor is operable to drive the turntable.

9. A system as claimed in Claim 8, in which the pulse motor includes a permanent

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. potentiometer continuously so that the indicated speed in degrees per minute corresponds exactly to the required degrees per minute reading on the chart corresponding to the time shown on the stop watch. The programmer periodically checks that the cumulative angle of rotation from the start position AA corresponds to the elapsed time from the commencement of rotation. This check is carried out by means of an electronic circuit which counts the pulses emitted by the pulse generator and divides by 26. This enables the circuit to provide a read out of the cumulative angle of rotation for every 0.1 rotation of the projector 22. When the pulse train for the complete approach channel 2 has been recorded, the tape recorded is switched off. On using the tape to drive the pulse motor 26, the centre of the projector beam will follow precisely the required speed profile of a particular ship travelling along the approach channel 2. In addition to the above described methods of obtaining a pulse programme, it is possible to use other programming methods using digital computer techniques. One method using digital computer techniques involves using a programme store and a processor. The programme store consists of a set of pre-wired sockets into which individual programme units can be plugged. These programme units are conventional Electrically Programmable Read Only Memories which will be referred to as E-PROMS. Each E-PROM will contain several programmes, and can be programmed by the manufacturer in response to appropriate supplied data. It is proposed to provide sufficient space for storing 100 programmes. The processor contains instructions for providing an output in response to the information fed to it from the programme store. The output from the processor is a series of pulses which is fed to the pulse motor 26 so as to rotate the projector 22 in accordance with the selected programme. WHAT WE CLAIM IS:

1. A speed indicating system for providing indication to the pilot of a moving ship of the ship's adherence to a desired speed profile as the ship travels along a predetermined path as defined by a harbour entrance channel, said system comprising: a source of electromagnetic energy, means for transmitting a central beam of said energy, means for transmitting discrete side beams of energy adjacent said central beam, said discrete beams being at frequencies different from one another and from the central beam, means for rotating said central and discrete side beams together, and on a common axis at a shore based location to cause said beams to intercept said predetermined path at substantiai angles, said means for rotating said beams including an electric pulse motor of the type having an output shaft capable of rotating through an angular displacement related to the number of electrical pulses in an input pulse train to the said motor and said motor shaft rotating at a speed related to the frequency of said pulses in said pulse train, and said pulse traip having a frequency which is variable to reduce the speed of rotation of the beams from a maximum at the channel entrance to a minimum at the inner end of the channel where the ship must be further manoeuvred for docking or the like.

magnet rotor and a pair of windings in quadrature which coact with the rotor.

10. A system as claimed in Claim 9, in which the rotor hays 24 poles.

11. A system as claimed in any one of Claims 8 to 10, in which the pulse motor is actuated by a programme stored on tape.

12. A system as claimed in any one of Claims 8 to 10, in which the pulse motor is actuated by a programme stored in a solid state memory.

13. A system as claimed in any one of Claims 6 to 12, in which the drive is applied to the turntable through a gear train.

14. A system as claimed in Claim 13, in which the gear train has a gear ratio of 9,600: 1.

15. A speed indicating system substantially as herein described and shown in the accompanying drawings.