GB2034471A - Sonar berthing aid - Google Patents

Abstract

In a berthing aid underwater sonar distance detecting units TB and TS mounted on a jetty J adjacent a berthing line BL determine the bow and stern "distances off" DB and DS of a ship S during a berthing procedure, and an intermediate sonar unit Ta determines an intermediate distance off A. Signal processing means which receive the signals from the units check the validity of the signals and determine the distances off DB and DS when the signals are valid. Signal validity is determined by checking that the equation a DIVIDED b (DS-DB) = A-DB is satisfied, a and b being the distances shown in Figure 3. <IMAGE>

Description

SPECIFICATION Measuring system This invention relates to system of the type which employ spaced distance detecting units to determine the "distances off" of corresponding points on a flat surface with respect to a measuring datum.

Systems of this type are used in navigation aids which determine berthing data to assist the pilot of a ship during a berthing operation, when the "slab" side of a large ship provides said flat surface and the berthing line of a jetty is said measuring datum. The invention is of particular, but by no means exclusive, application to navigation aids of this character and will mainly be described hereinafter with reference to such navigation aids.

Navigation aids as referred to are in use to provide pilots, particularly the pilots of large ships such as super tankers and bulk ore carriers, with information as to the angle of the ship with respect to the jetty, the distance of the ship therefrom, and the speed of approach. Installations are in use which provide a visual display of this data on the jetty within sight of the pilot, one such installation being described in our Patent Specification No. 1,384,647, although alternatively the data may be transmitted by radio to the pilot on board ship. The data is derived from two distance detecting units normally employing underwater sonar transducers and spaced apart so as to detect the distance from the jetty of respective bow and stern sections of the ship, normally referred to as the "fore and aft distances off" measured in relation to bow and stern fenders on the jetty.

Although such installations in general perform very satisfactorily problems have been encountered when, due to manoeuvring of the ship with resultant turbulence at the stern region or other causes, the signal from a detecting unit is materially affected with resultant determination and display of false data.

The object of the invention is to provide a measuring system of the type referred to which automatically checks the validity of the signals from the distance detecting units.

According to the invention a measuring system comprises three distance detecting units spaced apart along a datum line and operative to provide signals indicative of the "distances off" from the datum line of corresponding portions of a flat surface, signal processing means to process the signals from the units and which are operative to check the validity of the signals and to determine said distances off at least in respect of valid signals, validity being checked by computing that the equation a/b (B-C) = A-C as hereinafter derived is satisfied.

The signal processing means may operate to produce a signal indicative of received invalid signals in the event that said equation is not satisfied.

This signal may be employed to inhibit the determi nation of corresponding distances off, orto inhibit the display of invalid determined distances off, or for any other functional purpose.

When the system is embodied in a berthing aid the signal processing means preferably determine berthing data comprising both the distances off and the velocities of nominal bow and stern sections of the ship, as defined by fenders on the jetty, with two of the units appropriately positioned for this data to be determined directly from the signals therefrom.

The determined data may be displayed on the jetty so as to be visible to a pilot on board ship during the berthing operation, for example as in the installation described ih our said Specification No. 1,384,647.

The signal processing means preferably comprise a microcomputer or microprocessor programmed appropriately to process the signals, and to check that the foregoing equation is validly satisfied and if so to drive a large visual display of the berthing data visible from on board ship. If the equation is not satisfied the display of the invalid data is inhibited, and the microcomputer may be programmed to compute and display while invalid signals are received predicted data based on immediately past data the validity of which has been accepted.

The invention will now be further described with reference to the accompanying diagrammatic drawings which illustrate, by way of example, the underlying geometrical theory and practical illustrative embodiments. In the drawings: Figure lisa geometrical diagram; Figure 2 is a block circuit diagram of a measuring system representing one embodiment; Figure 3 illustrates a ship and jetty during a typical berthing operation, showing the positioning of three distance detecting units of a berthing navigation aid representing a second embodiment; and Figure 4 is a block diagram of the second embodiment.

Referring to Figure 1, in accordance with the invention three distance detecting units are respectively positioned at points Pa, Pb and Pc and operative to produce signals indicative of the "distances off" A, B and C of correspondingly spaced sections at Oa, Ob and Oc of a flat object 0 with respect to a datum line DL. As is the case in said second embodiment this flat object 0 may be the "slab" side of a large ship. Drawing of lines parallel to DL through Oa and Oc produces, as shown, similar triangles Oa.X.Ob and Oc.Y.Ob.If the spacing of the points Pa and Pc is denoted by a, and that of the points Pb and Pc by b as shown, then as the ratios of corresponding sides of similartriangles are equal, a/b = A-C/B-C or a/b (B-C) = A-C (1) which is the equation previously referred to and which, according to the invention, is utilised to check the validity of the received signals.

The relationship of equation (1) applies for any inclination of the object 0 relative to the datum line DL. If distance signals are received indicative of distances which do not satisfy the equation then at least one of the measured values is either in error or refers to measurement of an interposed surface, such as that presented by an inboard tug in respect of a berthing aid. Provided that three measurement signals are received fulfilling the consistency equation (1), then for practical situations there is a very high probability that a single flat surface (such as the slab side of a ship) is being measured. The validation of the equation may then be used to "accept" the measured values and they may be presented for display (as in a berthing aid, for example) with a high degree of confidence in their validity.In such an application it is preferred that the display of measured values be inhibited when they do not conform with the validity check.

It will be appreciated that more than three distance detecting units may be used, the signals therefrom being taken in selected groups of three units for the purpose of validity checking employing equation (1).

The system shown diagrammatically in Figure 2 utilises three sonar transducers Ta, Tb and Tc at the measuring points Pa, Pb and Pc. A sonar transmit/ receive unit STR connected to the transducers is triggered by strobe pulses from a clock circuit 1 which also commences counts by counters 2,3 and 4 of pulses from a pulse train generator 5. Return echo signals from the transducers produce output signals from the STR unit which respectively terminate the counts of counters 2,3 and 4. Thus the three counts, which are retained until the next strobe pulse starts a fresh counting cycle, are respectively proportional to the distances off denoted by A, B and C.It will be appreciated that the pulse frequency of the generator 5 may be so chosen relative to the sonar transit time that the counts are equal to the distances off being measured, as later discussed in detail with reference to the second embodiment.

The smallest count C is subtracted from the largest count B by a difference amplifier 6, the output (B-C) being multiplied by a set-in signal a/b in a multiplier circuit 7, to provide the lefthand term a/b (B-C) of equation (1). The count C is subtracted from A by a difference amplifier 8, providing the righthand term (A-C), and the two terms are compared using a difference amplifier 9 as a comparator. For consistency of the measured values the comparator output should be equal to zero within the tolerances of the measurements. Any discrepancy between the two terms results in a comparator output which is amplified by an amplifier 10 to provide a signal Si.

This signal, which may be positive or negative, can be used to inhibit the display of invalid measured values or their use in any other functional way.

In Figure 3 the ship is illustrated diagrammatically at Sand the berthing line of the jetty J is shown at BL, this corresponding to the datum line DL of Figure 1. Three underwater distance detecting units incorporating sonar transducers Ta, TS and TB are mounted on the jetty J, being spaced apart and positioned adjacent but a distance dslightly behind the berthing line BL. Thus they correspond to the units Ta, Tb and Tc of Figure 1, with TS and TB directly measuring the distances off Ds and D5 of stern and bow sections of the ship S.

Further relating to Figure 1, D5 and De respectively correspond to distances B and C and the corresponding distances A, a and hare marked in Figure 3. Thus for the practical berthing aid embodiment of Figures 3 and 4, equation (1) becomes a/b (DS - DB) = A- DB (2) Ds and De now being the stern and bow distances off to be determined.

Referring now to the block diagram of Figure 4, the complete berthing aid system comprises the sonar transmit/receive unit STR connected to the three transducer units Ta, TB and TS, and to a microcomputer unit MC comprising a microcomputer 11 and control panel 1 The microcomputer 11 provides a serial output to drive a remote visual display unit 12 on the jetty and a remote digital indicator 13. A separate serial output drives a cassette recorder 14, and a parallel output drives an alpha-numeric printer 15.

The software of the microcomputer 10 provides the 1 Hz strobe output on line 16 at the interface with STR, and all processing within the microcomputer is reiterative upon this 1 Hz rate. A trigger signal at TTL level is provided to fire the sonar transducers, and the microcomputer measures the duration between this transmission and the reception of reflected return signals by utilising a cyclic software count.

This count is as before interrupted by the reflected return signals and the count values, representative of the actually measured distances De and Ds to the ship S, are processed to provide a range measurement of bow and stern sections. The next transmission and return signals from the same transducers, occurring one second later, enable the microcomputes to make an initial calculation of ship velocity towards the berthing line.

The signal validation according to equaton (2) is implemented by the microcomputer 11 as part of the programming thereof. Any discrepancy inhibits display of the false measurements and while invalid signals are received the microcomputer computes and displays predicted "true" values based on the trend of the signals received immediately before the period of invalidity.

Any suitable count pulse frequency may be used, but advantageously this is such that the respective counts equal the distance concerned in length units.

In conditions of average salinity and temperature the velocity of sound in salt water is approximately 1500 metres per second. A fixed pulse frequency could result in a reduction in the accuracy of measurement unless some form of compensatory device is included. Hence the system is capable of adjusting the pulse frequency or the processing constants according to any given set of operational parameters and their expected deviation, in order to maintain the counts equal to the measured distances.

The microcomputer 11 automatically compensates for the spacing of the transducers the distance behind the berthing line BL. Thus fender deflection is represented as a determined negative range at the bow and stern measuring points, i.e. determined ship movement beyond the berthing line BL.

The control panel 11 has an ON/OFF switch 17, a multi-position swich 18 which enables the system to be switched to any one of a number of jetties with which it is alternatively used, a keyboard 19 positioned behind a lockable flap, and a digital LED display 20. The keyboard 19 is used to preset inputs into the microcomputer memory, these largely being jetty configuration dependent but also enabling test routines to be established. The keyboard 19 also provides a facility for system clock adjustment, and typical preset inputs are the distances a and b between the transducers, the average datum temperature value appropriate to the geographical site, which affects the sound velocity, and control parameters for the jetty display 12 which is of a scale such that it is visible to a pilot on board the ship.The switch 18 selects the correct microcomputer memory inputs for the preset parameters of the jetty selected in conjunction with the appropriate transducer set.

The panel display 20 has four LED numeric displays, distance off and velocity for the bow section and distance off and velocity for the stern section of the ship. The jetty display 12 is generally as described in our said Specification No. 384,647 and well known as "The IDASAT" (Integrated Distance and Speed and Tilt) Berthing Display, and hence it is not illustrated in detail in the drawings. It is an integrated symmetrical visual display with an illuminated Jetty Datum line at the top and an illuminated Distant Datum (for example 100 metres) at the bottom. Two vertical columns of distance bars respectively representative of bow and stern section ranges extend between the Jetty and Distant Datum lines and they are progressively illuminated (intense white) as the ship approaches the jetty.

At each side of the display there is a vertical row of three (respectively green, amber and red) indicator lights, one row for the bow section and one for the stern section, and these are illuminated according to the computer programming to indicate velocity ranges. A steady green indicator light indicates that the ship is within a programmed safe speed range; a flashing amber indicator light indicates a marginally safe speed range; and a flashing red indicator light indicates a dangerous speed range.

Claims (13)

1. A measuring system comprising three distance detecting units spaced apart along a datum line and operative to provide signals indicative of the "distances off" from the datum line of corresponding portions of a generally flat surface, signal processing means to process the signals from the units and which are operative to check the validity of the signals and to determine said distances off at least in respect of valid signals, validity being checked by computing that the equation a/b (B-C) = A-C is satisfied, where A, B & C are the determined distances off with respect to the three units taken in order along the datum line, a is the distance between the second and third units when considered in that order, and b is the distance betwen the first and third units when considered in the same order.

2. A system according to claim 1, wherein the signal processing means are operative to produce a signal indicative of the reception of invalid signals in the event that said equation is not satisfied.

3. A system according to claim 2, wherein said signal indicative of the reception of an invalid signal is employed to inhibit the determination of corresponding distances off.

4. A system according to claim 2 or 3, wherein said signal indicative of the reception of invalid signals is employed to inhibit the display of corresponding distances off.

5. A system according to any one onf claims 2 to 4, wherein said signals from the distance detecting units comprise trains of electrical pulses and the signal processing means comprise first, second and third counters to which said signals are respectively fed, the counts of said counters thereby being indicative of the measured distances off, a first difference amplifier the two inputs of which are the counts of the first and third counters to provide a first amplifier output representing (B-C), a second difference amplifier the inputs of which are the counts of the second and third counters to provide a second amplifier output representing (A-C), a multiplier circuit with two inputs provided by the first amplifier output and a set-in signal a/b to provide a multiplier circuit output representing a/b (B-C), and a third difference amplifier operating as a comparator and the two inputs of which are provided by the outputs of the second difference amplifier and of the multiplier circuit, said signal indicative of the reception of an invalid signal being an output signal of the third difference amplifier.

6. A system according to claim 1, wherein the signal processing means comprise a microcomputer or microprocessor programmed to process the signals provided by said distance detecting units and to check that said equation is validly satisfied.

7. A system according to any one of the preceding claims, embodied in a ship berthing aid and operative to determine berthing data comprising both the distances off and the velocities of nominal bow and stern sections of the ship, as defined by the position offenders on a jetty.

8. A system according to claim 7, wherein said first and third units are so positioned and fixed relative to the jetty that the berthing data relating to said bow and stern sections can be determined directly from the signals from these two units.

9. A system according to claim 6 and either one of claims 7 and 8, wherein the system is associated with a large visual display of the berthing data which is positioned on the jetty so as to be visible to a pilot on board ship during the berthing operation, said microcomputer or microprocessor being programmed to drive the display in the event said equation is validly satisfied with the display of invalid data being inhibited in the event the equation is not so satisfied.

10. A system according to claim 9, wherein the microcomputer or microprocessor is programmed to compute and display, while invalid signals are received which do not satisfy said equation, predicted data based on immediately past data the validity of which has been accepted.

11. A system according to any one of claims 7 to 10, wherein the distance detecting units are underwater sonar units positioned adjacent the berthing line on the jetty.

12. A berthing aid embodying a measuring system according to any one of the preceding claims.

13. A berthing aid constructed and arranged substantially as herein particularly described with reference to Figure 2, or Figures 3 and 4, of the accompanying drawings.