SONAR SYSTEM

Abstract: A sonar system suitable for small and medium sized boats which scans ahead, to port and to starboard, preferably at a distance related to depth below. The system includes a display (40) using series of LCD segments orientated in directions representative of the directions of scanning so that the displayed information can be instantly interpreted. Signals are displayed continuously until updated. The system also includes a transducer assembly for scanning in a plurality of discrete scanning directions.

Description: "SONAR SYSTEM" The present invention relates to a sonar system which is particularly, but not solely, suited for small and medium sized vessels such as private pleasure yachts and small commercial vessels. The invention is particularly useful when cruising near coral reefs and navigating narrow channels through mud and sand banks since the invention not only measures depth, but also scans ahead and to port and starboard. BACKGROUND ART Although lateral scanning radar and sonar systems are known, such systems are complex and expensive, and as such, are only suitable for large scale vessels such as navy craft. In known lateral scanning radars and sonar, rotating cathode ray tube displays are used. In such displays, the old signals fade as new signals on the rotating arm are displayed. Moreover, the cathode ray tube is difficult to read in bright sunlight as it does not provide a high contrast display. SUMMARY OF THE INVENTION It is an object of the present invention to overcome, or substantially ameliorate, at least one of the above described disadvantages by providing an economical sonar system suitable for small and medium sized boats which provides forward, port and starboard scanning as well as depth scanning. According to the present invention, there is provided a sonar system for a boat for scanning ahead, to port and to starboard, said system comprising transducer means for transmitting scanning signals in a plurality of discreet scanning directions including ahead of the boat, to port and to starboard; electronic control means for activating said transducer means to transmit said scanning signals sequentially in said plurality of directions; receiving means for receiving the transmitted signal after reflection from objects; signal processing means connected to the output of said receiving means for determining distances of said objects from the received signals; and display means connected to said signal processing means for displaying the determined distances in their respective directions. Preferably, the sonar system has a display which utilises liquid crystal display (LCD) segments which display a measured value continuously until superceded by a newly measured signal. Preferably, the sonar system monitors depth ahead at a distance related to the depth below. The depth ahead range can be set manually, or calculated automatically from the depth below. Typically, depth ahead (as well as depth to port and depth to starboard) are measured at a distance approximately six times the depth below. If desired, the sonar system can incorporate transducer means and associated display means for measuring and displaying depth abeam, or even depth aft. Since the measured signals representing depth to port, ahead, starboard and below, are displayed continuously until updated, a simultaneous display of all signals is obtained. Moreover, by arranging the LCD segments in a suitable pattern, a quasi-analog display can be obtained. Preferably, the sonar system incorporates an alarm which is activated when the depth ahead varies more than a selected amount. This amount may be related to the depth below. Typically, the alarm volume increases and/or its pitch increases as the vessel approaches an obstacle such as a reef. In further preferred embodiments, different alarm tones are provided so that the operator is immediately able to distinguish audibly between obstacles to port, starboard and ahead. Typically, the display means is capable of displaying a number of depth ranges. If the measured signal falls outside the selected range, an alarm is activated to indicate that the range selection requires changing or the gain requires adjustment. The sonar system incorporates a transducer arrangement for transmitting and receiving signals in the required directions. In one embodiment, a transducer is provided for each scanning direction. Each transducer is connected - sequentially for a period of time sufficient to transmit and receive an echo from the maximum range selected. In another embodiment, a single transducer is physically orientated to the required scanning direction. The received echo is quantised to a number of time levels, and stored and displayed until the next echo is received for that particular scanning direction. The number of time levels is related to the number of display segments selected for the display means. The transducer arrangement is preferably mounted on a single gimballed assembly mounted inside the hull of a glass reinforced plastic vessel, or mounted externally and protected by a glass reinforced plastic or ABS plastic hydrofoil protective cover. Notwithstanding any other forms of the present invention, preferred embodiments thereof will now be described with reference to the accompanying drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic plan view of a scanning pattern of a sonar system according to one embodiment of the present invention; Fig. 2 is a side elevational view of the scanning pattern of Fig. 1; Fig. 3 is a plan view of the scanning pattern of one beam of Fig. 1; Fig. 4 illustrates one display layout for the sonar system; Fig. 5 is a schematic block circuit diagram of the sonar system according to another embodiment of the present invention; Fig. 6 is a schematic block circuit diagram of the signal processing circuit of Fig. 5; Fig. 7 is a schematic block circuit diagram of part of the circuit of Fig. 6; Fig. 8 is a schematic block circuit diagram of a clock circuit for use with the embodiment of Fig. 5; Fig. 9 illustrates timing pulses for the circuit of Figs . 5 to 8 ; Fig. 10 is a cross-sectional plan view of a transducer arrangement of one embodiment; Fig. 11 is a cross-sectional plan view of a transducer arrangement of another embodiment; Fig. 12 is a side elevational view of part of the transducer arrangement of Fig. 11; and Fig. 13 is a cross-sectional side elevational view of the transducer arrangement of Fig. 11. DESCRIPTION OF PREFERRED EMBODIMENT As shown in Figs. 1 to 3, the sonar system of one embodiment of the present invention is designed to scan ahead and to port and starboard, as well as measuring depth (not shown). The beams typically have a horizontal beamwidth between 15° and 30°, and a vertical beamwidth of 7 to 10 . The transducer assembly is gimballed so that the beams are tilted almost straight ahead to provide maximum range in shallow water. Although five scanning directions are shown in Fig. 1, any reasonable number of scanning directions can be obtained by suitable design of the transducer means. The design of the transducer means will be described below. For the sake of simplicity, the following description relates to a scanning pattern having three beams: port (P), ahead (A) and starboard (S) as well as depth measurement. The circuit diagram for the sonar system is shown in Figs. 5 to 8. A first clock 50 generates a pulse train as shown in Fig. 9. The period of the first clock is greater than the maximum time required for a signal to be transmitted and received from the maximum desired range. An output of the clock 50 drives a 1 to 5 and restart decade counter 53 which provides sequential outputs MD, P, A, S and D as shown in Fig. 9. The output of the counter 53 is connected to a transducer multiplexer/driver 55 which sequentially activates the respective transducer for the port, ahead, starboard and depth beams, or orientates a single transducer in either the port, ahead, starboard or depth direction. The latter system will be described in more detail below. Each pulse from the first clock 50 also passes to a delay circuit 51 where it is delayed, typically by 10ms. A narrow pulse (typically 2ms) is generated for every pulse from the clock pulse 50 as shown in wave form T in Fig. 9. The narrow pulses T activate a transmitter 52 having an oscillator therein, and also reset a counter 61 in a signal processing circuit 60. The 10ms delay is provided in order to allow reed switches which connect the transducers to operate before the transmitter pulse is fired. This prevents sparking across the contacts and radio frequency interference. On receipt of each narrow pulse, the transmitter 52 will transmit a signal through the transducer 54 selected by the transducer multiplexer/driver 55. The signal is of suitable frequency e.g. 160KHz. The signal is transmitted in the direction in which the transducer 54 is orientated, and received by receiver 56 after reflection from obstacles such as reefs, sandbanks, etc. The received signal is amplified in a tuned amplifier stage 57 with manual gain control and/or automatic gain compensation in which the signal level is multiplied by a ramp voltage proportional to the time delay between the transmitted and received pulse. This time varying gain (TVG) compensates for normal attenuation of the signal through the water. An additional gain control stage can be included to reduce the gain for distances between zero and five times the depth below. This gain stage would be controlled by the period of the received echo from the bottom. Such gain controllers can be provided on the front panel of the sonar display 40 (Fig. 4) to enable the operator to adjust the gain of signals close to the vessel, and those further away from the vessel which in turn, permits the operator to choose between the detection of fish nearby or the distant detection of reefs and other obstacles. The amplified received pulse is then envelope detected in detector stage 58 and thereafter passed through a filter stage 59 to remove short radio frequency interference spikes. The signal output from the filter stage 59 is then input to a signal processing stage 60 shown in more detail in Fig. 6. As shown in Fig. 6, the signal is passed through circuit 62 if it represents a longer, higher level echo or through circuit 63 if it represents a shorter, small echo such as would be caused by fish. A discriminator circuit can be used to distinguish between the two types of echoes. A three position switch 65 allows the operator to choose whether to display long or short echoes, or both. An external control (not shown) can be provided on the front panel of the display so that it is possible to adjust the threshold level of the small echoes. An additional "white line" stage as used in chart recorders can be included to display fish close to the bottom which would not normally be displayed separately from the bottom signal. Signals which have been recognised by circuit 62 as being long echoes are used to trigger monostable 64 which has sufficient pulse length to trip all levels of the display. If both short and long echoes are chosen by switch 65, the short echoes (e.g. fish echoes) are displayed by the illumination of extra LCD bars above the depth reading. The signal processing circuit 60 comprises a cyclic counter 61 which provides 21 sequential pulse outputs and then resets. The counter 61 is reset by every narrow pulse derived from the clock 50 and is used to measure the time difference between the transmitted " and received pulses. Connected to outputs 5 to 21 of the counter 61 are 16 sub-circuits Al, A2 A16. The number of sub-circuits corresponds to the number of LCD segments in each beam display (see Fig. 4); this number can be varied as desired by appropriate modification of the counter 61. One sub-circuit is illustrated in more detail in Fig. 7. The echo signal selected by switch 65, the (reset) narrow pulses from clock 50 and an output (timing) pulse from the appropriate output of counter 61 are input to an AND gate 71, the output of which is connected to monoβtable 70. Hence, the monostable which is tripped corresponds to the elapsed time of the received echo. The time period of the monostables 70 is greater than the period of the first clock 50. The output of each monostable 70 is switched by switch/multiplexer 72 to one of four flip-flops (FFP, FFA, FFS, FFD) according to the signal from a corresponding output (P, A, S, D) from counter 53. The control signals P_ K, A_Λ, S_K, D_tt which operate the flip-flops are derived from the output 21 of counter 61 via circuit 69. The outputs of the flip-flops FFP, FFA, FFS, FFD for sub-circuit A(N) are connected to the Nth segments of the port, ahead, starboard, depth displays respectively. Changing the range of the display can be accomplished by changing the frequency of the "range clock" input of counter 61. The range clo:ck frequency can be set manually to a predetermined fraction of the clock 50 frequency, or it may be set automatically by using an automatic range selection circuit such as that shown in Fig. 8. In the automatic range selection circuit, the full scale range of the port, ahead and starboard channels is made nominally ten times the distance of the depth below. In the automatic range selection circuit, a second clock 80 drives a decade counter 82 via a divider ( 20) stage 81. The decade counter 19 is reset by each MD pulse generated by the counter 53. In addition the counter 19 is stopped by the echo signal at the output of monostable 64. The value of the counter (between 1 to 200) at the time when the "stop" signal is received is stored by the counter 82 until the next MD pulse from counter 53. This value represents the depth of water below the boat and is used to set the divider stage 83 so that the output of the divider stage 83 is the frequency of the clock 80 divided by the currently stored count in counter 82. An additional divider ( 10) stage 84 is switched in on the P, A, S cycles of counter 53. The stored count of the counter 82 is displayed in a digital display 85 on the display panel 40. Alarm circuits are provided to warn of any decrease in depth to port, ahead or starboard in advance without travelling directly over that spot. In addition, the alarm circuits perform this function without requiring constant manual adjustment of the minimum depth to be alarmed as in conventional depth founders. The use of an automatic range selection circuit, as illustrated in Fig. 8, allows the alarm circuit to be simplified. As shown in Fig. 7, the output of each flip-flop (FFP, FFA, FFS) on the port, ahead and starboard display outputs is taken to a resistor adder circuit 68 so that the more display levels illuminated, the greater the alarm volume and/or the higher the alarm pitch. In the long echo pulse threshold mode, the closer the boat gets to an obstacle such as a reef, the more flip-flops are switched on and hence, the louder the alarm and/or the higher its pitch. An additional alarm circuit can be included to warn of minimum depth below. This can be adjustable to select a depth, typically between one and twenty metres. Furthermore, another alarm can be added to the depth below circuit to alarm if the depth exceeds a selected value, thereby acting as an anchor watch alarm. A typical display panel 40 is illustrated in Fig. 4. Five scanning directions are illustrated on the panel: two to port, two to starboard and one ahead, as well as a digital depth measurement. Each LCD segment of the display forms an arcuate band of the displayed scanning beam. Such an arrangement of the LCD segments creates a quasi-analog display thereby allowing the operator to tell at a glance whether any obstacles lie ahead, to port, or to starboard. The flip-flops driving the LCD segments are held on or off during each cycle, rather than flashed on and off rapidly as in multiplex display systems which appear constant due to the persistence of vision but which do not provide maximum contrast in bright sunlight. Moreover, the operator is able to tell immediately whether objects detected by the sonar are obstacles such as reefs, sandbanks or merely reflections due to fish. Other suitable display means such as cathode ray tubes, multi-pen chart recorders or digital printers, can be fitted to the apparatus of the present invention to suit particular applications such as the charting of channels. Such display means operate on each cycle of the first clock 50. It will be apparent to those skilled in the art that much of the hardware in the abovedescribed circuits can be replaced by a programmed microprocessor. For example, the microprocessor can be programmed to determine the interval between transmission and reception of a signal, and to display the measured interval on the appropriate beam on the display 40. A transducer assembly is shown in Fig. 10. Separate transducers T p , T A , T_ and provided to scan port, ahead and starboard. The transducers are embedded in a casting 101 made from epoxy and granulated cork. A lead balance weight 100 is provided to balance the casting 101 about the shaft 102. When the shaft 102 is mounted on suitable bearings (not shown), the angle of scan of the transducers can be varied quite simply. The casting 101 can also be mounted in a special frame (described below) in order to stabilise the transducer assembly against pitch and roll. Another transducer T D (not shown) is provided in a downward orientation for depth measurement. The abovedescribed transducer arrangement can be replaced by a single pivotable transducer as shown in Figs. 11 to 13. In this embodiment, a single transducer T. is used to scan port, ahead and starboard. The transducer T., is set in a casting 110 made from a mix of epoxy and granulated cork in order to reduce the effect of signals from the back face of the transducer. The casting 110 also contains an iron bar or permanent magnet 118, and lead balance weights 115 which balance the casting 110 about a shaft 111. The casting 110 is pivotable about its shaft 111 on bearings 112 set in a gunmetal housing 116. Electromagnets E_, E-, E_ are also mounted on housing 116. Each electromagnet E p , E_, E g corresponds to a respective scanning direction port, ahead, starboard. In order to scan in the different directions, the electromagnets are energised sequentially to cause the casting 110 to rotate until the iron member 118 in the casting 110 is opposite the energised electromagnet. Each electromagnet is energised for a sufficient period of time to allow a signal to be transmitted and received from the maximum range selected. Means are also provided to switch the output of the transducer T 1 to the display beam corresponding to the energised electromagnet. Although only three electromagnets are shown, it will be apparent to those skilled in the art that any suitable number of electromagnets at spaced intervals can be provided in order to scan in a plurality of directions. The housing 116 is pivoted about spindles 117 in frame 120 so that the housing 116 remains level as the vessel pitches up and down. In addition, the frame 120 is pivoted about bearings 113 so that the frame 120 and casing 116 remain level as the vessel rolls from side to side. The bearings 113 are mounted in a gunmetal casting (not shown) fixed to the bottom of the hull of the vessel. A second transducer T. is provided to measure the depth below. The transducer T, is pivoted about an axis 114 on frame 120 and is stabilised against pitch. Instead of providing a separate transducer ~~ 2 for measuring depth below, the transducer T. can be pivoted at point 119 so that it can be tilted to scan downwardly. An additional set of electromagnets 121 are installed along arc 122 and an additional iron bar is set above T-. in order to implement the downward tilting of T . The additional electromagnets 121 become part of casting 110 and T 1 rotates within casting 110. The casting 110 would also need to be re-balanced about shaft 111. The iron bar 113 in casting 110 can be replaced by a permanent magnet or an electromagnet energised at the same time as E p , E,, E g . In addition, opposing magnetic fields can be generated by reversing the current direction through the electromagnets not being scanned, i.e. E_ and E- would have opposing fields to the iron bar 118 while E, and iron bar 118 are energised by attracting fields. On a cruising yacht where only limited electric power is available, the iron member 118 is preferably a permanent magnet. A reverse field applied to each electromagnet E_, E Λ E e for a short instant when the energising electric A 5 field is turned off leaves a weak opposing field on each unenergised electromagnet due to the magnetic hysteresis of its iron core. Thus, only the energised electromagnet would be attracting the iron bar or magnet 118 while the unenergised electromagnets would be repelling the iron bar or magnet 118. The foregoing describes only some embodiments of the present invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims.

Claims: CLAIMS 1. A sonar system for a boat for scanning ahead, to port and to starboard, said system comprising transducer means for transmitting scanning signals in a plurality of discreet scanning directions including ahead of the boat, to port and to starboard; electronic control means for activating said transducer means to transmit said scanning signals sequentially in said plurality of directions; receiving means for receiving the transmitted signal after reflection from objects; signal processing means connected to the output of said receiving means for determining distances of said objects from the received signals; and display means connected to said signal processing means for displaying the determined distances in their respective directions. 2. A sonar system as claimed in claim 1 wherein said display means comprises a plurality of series of liquid crystal display segments, each orientated in a direction representative of a respective one of said scanning directions, the distance of an object detected in a particular direction being indicated by the number of LCD segements illuminated in the corresponding series. 3. A sonar system as claimed in claim 1 or 2, wherein said transducer means comprises a plurality of transducer elements each orientated in a respective one of said scanning directions. 4. A sonar system as claimed in claim 1 or 2, wherein said transducer means comprises a transducer element pivotable for orientation in any one of said scanning directions. 5. A sonar system as claimed in claim 4, wherein said transducer is pivotable in a casing comprising a plurality of electromagnets orientated in directions corresponding to said scanning directions, whereby said transducer element is orientated sequentially in said scanning directions by sequential energisation of said electromagnets. 6. A sonar system as claimed in any preceding claim, further comprising depth measurement and display means. 7. A sonar system as claimed in claim 6, wherein said transducer means scans at a distance related to depth of water below said boat. 8. A sonar system as claimed in any preceding claim, further comprising alarm means connected to the output of said signal processing means for providing an alarm upon detection of objects within a predetermined distance. 9. A sonar system as claimed in claim 8 wherein said alarm provides an audio signal whose volume is indicative of the distance of a detected object. 10. A sonar system as claimed in claim 8 wherein said alarm provides an audio signal whose tone is indicative of the distance of a detected object. 11. A sonar system as claimed in any preceding claim, wherein said signal processing means comprises a microprocessor.

Inventors: LEVY DESMOND JAMES, LEVY, DESMOND, JAMES
Applicants: LEVY DESMOND JAMES, LEVY MARILYN KAY, LEVY, DESMOND, JAMES, LEVY, MARILYN, KAY
Application year: 1983
Main classification: G01S7
IPC codes: G01S7, G01S15