GB2074392A

GB2074392A - A method and apparatus for burying an underwater cable

Info

Publication number: GB2074392A
Application number: GB8110355A
Authority: GB
Original assignee: Kokusai Denshin Denwa KK
Current assignee: KDDI Corp
Priority date: 1980-04-03
Filing date: 1981-04-02
Publication date: 1981-10-28
Also published as: GB2138940A; GB8325932D0; GB2074392B; GB2138939A; GB8325931D0; GB2138939B; GB2138940B

Abstract

Apparatus for burying a previously laid underwater cable 2 comprises a remote control tracking vehicle 3 having tracks 5 provided with an ultrasound receiver 11 for picking up signals sent from the location of the cable, means 9 for engaging the cable, means 8 for sensing the lateral displacement of the cable from the vehicle's centre line whereby the vehicle can follow the route of the cable, and means 7 for burying the cable. <IMAGE>

Description

SPECIFICATION A method and apparatus for burying an underwater cable This invention relates to a method for burying an underwater cable apparatus therefor. The cable may be a communication or electric power cable and it may be required to bury the cable in the sea bed in order to protect the cable from anchors of vessels or fishing tools.

When a cable has to be buried in the sea bed, a burying device is generally tugged by a mother ship to lay and simultaneously bury the cable. More particularly, in this method, a cable is placed within the burying device in advance on the mother ship, the burying device is lowered down onto the marine bed, and the burying device is tugged by the mother ship so that an excavation member provided on the burying device can dig a groove on the sea bed, whereby the cable is laid and also buried in the groove at the same time.This method is superior in ease of use and efficiency when a cable is to be newly laid and buried in the sea bed; however, when applied to a part of a cable which has previously been buried under the sea bed and which has broken, and, after being pulled up and repaired on the mother ship, is to be buried again, the method involves such difficulties that a special mother ship is required with the exceptional capability of being able to guide a burying device along the already buried portion of the cable. Further, since buried cables tend to take a tortuous rather than a straight course due to tidal currents, it is extremely difficult to detect accurately the place where the repaired cable should be buried. This unavoidably leads to leaving considerable portions thereof unburied.

Moreover, since this method necessitates the cable to be engaged within the burying device in advance on the mother ship and then lowered onto the marine bed by using a lowering rope or cable, the cable to be laid may become entangled with the lowering rope due to the influence of tidal current. It is then necessary for the operation to be stopped.

Sometimes the cable itself may be damaged by twisting or breaking.

The present invention focuses upon such drawbacks of the conventional methods and aims at providing a method and a device therefor which can effectively as well as accurately bury a cable under water not only when a cable is to be newly laid and buried but also when a cable has to be reburied.

The present invention provides apparatus for burying an underwater cable in the bed of a body of water, comprising means for locating a cable laid on said bed, means for driving the vehicle over said bed, means for engaging the cable and means for progressively burying the cable.

The invention includes a method for burying an underwater cable laid on the bed of a body of water using apparatus described above, which method comprises locating the cable by the cable locating means of the apparatus, bringing the apparatus to the cable and engaging the cable in the cable engaging means of the apparatus and causing the apparatus to progress along the route of the cable progressively burying the cable.

The invention also includes an ultrasonic oscillator to be mounted on a cable to enable the cable to be subsequently located which comprises a support frame mounted on the outer periphery of the cable, and a rotatable member mounted on said support frame in a freely rotatable fashion which rotatable member is provided with an ultrasound receiving element.

The invention further includes a cable position confirming device for apparatus for burying an underwater cable which device comprises four ultrasonic receiving elements are provided on the cable burying apparatus at the corners of a horizontal rectangle and an ultrasonic transmitter/receiver element provided at the centre of the square.

The present invention will now be illustrated by the following detailed description of preferred embodiments with reference to the attached drawings.

Figure 1 schematically indicates states where a cable is laid on the sea bed and is buried thereunder. Figure 2 shows a preferred embodiment of apparatus according to the present invention in a side and a frontal views. Figure 3 schematically indicates the state where the burying apparatus is guided to approach a cable. Figure 4 provides frontal and top views of the structure of an ultrasonic detection system suitable for apparatus of the kind shown in Fig. 3 and schematic illustrations of the circuitry used to process ultrasonic signals received.

Figure 5 is a schematic view to illustrate the whole structure of another cable burying apparatus of the invention. Figure 6 is a schematic view to show an ultrasonic wave transmitter/receiver attached to a cable as a cable position confirmation device to be used in guiding the cable burying apparatus to the cable, and Figure 7indicates an embodiment of an ultrasonic oscillator to be mounted on the cable in advance wherein Figure 7 (a) is a frontal cross sectional view and (b) a side cross sectional view. Figure 8 is a diagram to explain the principle by which the position of the cable is determined by the apparatus of Fig. 5. Figures 9 (a) and (b) are block diagrams to indicate an example of a method of processing signals generated from the ultrasonic transmitter/receiver on the cable and received by apparatus according to the present invention.Figure 10 is a view from helow to illustrate another embodiment of an ultrasonic transmitter/receiver.

Figure 11 provides a front and a side view of an embodiment of a cable engaging member einployed in apparatus according to the present invention, while Figure 12 provides frontal views showing in greater detail the operation of the cable engaging mechanism of Fig. 11.

Figure 13 is a side view to illustrate the whole structure an another burying apparatus according to the present invention; Figure 14 illustrates one preferred embodiment of the cable clamp member of the burying device illustrated in Fig. 1 3 wherein (a) is a frontal view and (b) a side view. Figure 15 is a view to explain a procedure for catching and clamping a cable. Figure 16 illustrates another preferred embodiment of the cable clamp member of the burying device illustrated in Fig. 1 3 wherein (a) is a front view and (b) a side view. Figure 17 shows a preferred embodiment of the cable engaging member of the burying device illustrated in Fig. 1 3 wherein (3) is a frontal view and (b) a bottom view.

Fig. 1 (a) shows the state where a cable 2 is laid on a sea bed 1 while Fig. 1 (b) the state where the already laid cable 2 is buried under the sea bed 1. The method for burying a cable method and the apparatus therefor hereafter described are intended to provide a method and an apparatus which, under substantially any conditions, can effectively and accurately transform the state shown in Fig. 1 (a) to the state in Fig. 1 (b).

Fig. 2 shown the general structure of an embodiment of a burying apparatus 3 to be used to carry out the method of the present invention. The apparatus 3 can be driven over the sea bed 1 by endless tracks 5. Naturally some other suitable means for the purpose can be employed. Endless tracks, 5 are operated by energy supplied from the mother ship (not shown), for instance electric power supplied through a control cable 4. On the middle portion 6 of the apparatus 3 is provided an excavation means 7 to crush or displace sand and earth and thus dig a groove on the sea bed. For instance a water jet nozzle and a water pump (not shown) may be used to dig the groove.A cable engaging means 9 is provided on the middle portion 6 of the front end of the apparatus 3, in front of the excavation means 7, which engaging means has a sensor 8 to measure the amount of lateral displacement of the cable relative to the apparatus. The cable 2 is guided through the engaging means 9 into the middle portion 6 and finally onto the groove excavated by the excavation means 7 to be buried therein. The excavation means 7 and the cable engaging means 9 are driven by an energy supplied from the mother ship, for instance electric power supplied through the control cable 4 in a similar manner to the means 5 for driving the apparatus over the sea bed.

Fig. 3 indicates the procedure by which the apparatus 3 according to the present invention approaches towards the cable 2 laid upon the sea bed 1. The cable 2 is provided with a transmitter 10, for instance an ultrasonic oscillator prior to the laying operation in order to indicate its location. A signal from the transmitter 10 can be received by a receiver 11, for instance an ultrasonic wave receiver, provided on the apparatus 3, and the direction from which the signal comes may be obtained by calculation. Therefore, the apparatus 3 can be guided to approach the cable 2 by driving the tracks 5 and by controlling a travelling control mechanism (not shown), the control being based upon the result of the signals received by the receiver.The apparatus 3 may possibly be controlled to be guided near and onto the cable 2 by using images conveyed to and displayed on the mother ship by from a TV camera carried on the apparatus. In the case where the control by a TV camera is difficult due to high turbidity in the water, however, it is more effective to use the aforementioned ultrasonic detection system or other systems such as an AC magnetic field detector, a metal detector, or a magnetic detector. The present invention includes the systems such as are identified above and all the systems whereby a burying apparatus can approach a cable by receiving output transmitted from a transmitter mounted on the cable using a receiver mounted on the burying apparatus.

Fig. 4 shows an example of a system to make apparatus 3 approach a cable 2 using the above mentioned ultrasonic detection system. More particularly an ultrasonic receiving element 1 102 of an ultrasonic wave receiver 1101 having a sharp directivity within a horizontal plane is mounted on an arm 1103 in a manner so as to be rotatable by a rotary drive device 1104 for scanning in a horizontal plane. The revolution by the rotary drive device 1 104 rotates the shaft of a potentiometer 1106 through a transmission gear 1105. The rotary drive device 1104 and the potentiometer 1106 are mounted on a table 1107 and the table 1107 is fixed on the apparatus 3 (not shown). The output from the ultrasonic receiving element 1102 is guided consecutively through a slip ring 1 108, and band pass filter 1109, an amplifier 1110 and a detector 1111 to be detected and is given a pulse output. A voltage 2E is fed between fixed contacts of the potentiometer 1 106, the voltage at the moving contact of the potentiometer 1102 is adjusted to make the ultrasonic wave receiver element 1102 become precisely at E in a direction in front of the burying device 3 (not shown).If the ultrasonic wave receiving element 1 102 is rotated clockwise by the rotary drive device 11 04, as indicated in Fig. 4 (c), the voltage at the moving contact of the potentiometer 1106 moves from 0 to E while the ultrasonic wave receiving element 1102 travels from a position directed behind of the burying device 3 (not shown) to a position directed in front thereof, in other words from 0" to 1 80'.

Similarly, the voltage at the moving contact of the potentiometer 1106 moves from E to 2E while the ultrasonic wave receiving element 1102 travels from a pbsition directed in front of the burying device 3 (not shown) to a position directed behind thereof from 180 to 360 , repeating such movements of the scanner will produce a saw-tooth wave form in the potentiometer output.

A portion encircled by a dot-and-chain line in Fig. 4 (d) denotes a travelling control circuit wherein the reference numerals 1112, 111 3 denote comparators, 1114, 111 5 voltage sources (specifically 111 4 denotes a voltage E-a, 111 5 a voltage E + a) wherein a is a small value. The reference numerals 111 6 and 111 7 denote AND circuits while 111 8 and 111 9 denote output terminals.When the voltage at the moving contact of the potentiometer 1106 is less that E-a, the output from the comparator 1112 becomes "HIGH" while the output from the comparator 11 3 becomes "LOW" and when the voltage at the moving contact of the potentiometer 1106 is from (E + a) to 2E, the output from the comparator 1113 becomes "HIGH" while the output from the comparator 111 2 becomes "LOW". Therefore, if the ultrasonic wave receiver element 1102 receives an output from the ultrasonic oscillator 1001 at a location to the left of the apparatus 3 (not shown), or, in other words, a position between 0" and (180 - p) wherein ss is a small value), and a pulse output is transmitted from the detector 1111, since the output from the comparator 111 2 is kept at "HIGH" between 0" and (180 -p), the AND circuit 1116 becomes "HIGH" to feed an output to the output terminal 111 8 as well as to feed an output to the counterclockwise control circuit of the apparatus 3 (not shown). During this period the output terminal 111 9 assumes 0 status.The ultrasonic wave receiving element 1102 receives an output transmitted from the ultrasonic oscillator 1001 at a position to the right of the apparatus 3 (not shown) or between 180 and (360 -p) (wherein p is a small value) to generate a pulse output at the detector 111 since the output from the comparator 111 3 is kept at "HIGH" between 180 and (360 -p), AND circuit 1117 becomes "HIGH" and an output is fed to the output terminal 111 9 to supply an output to the clockwise control circuit of the apparatus 3 (not shown).During this period the output terminal 1 8 assumes the 0 state. Following the above procedure, the output transmitted from the ultrasonic oscillator 1001 mounted on the marine cable in advance can be transmitted to the u.ltrasonic wave receiver 1101 mounted on the apparatus 3 so as to make the apparatus 3 approach toward the marine cable.

Fig. 5 in a schematic view to illustrate the general structure of another cable burying apparatus 3, showing a situation in which a cable 2 that has been laid on the bottom of a body of water is being buried by the cable burying apparatus 3. The cable burying apparatus 3 is provided an ultrasonic transmitter/ receiver 11 as a device to confirm the position of the cable. The position of the cable 2 is confirmed by the data obtained from said ultrasonic transmitter/receiver 111. The device thus can be guided to run along the cable 2 by driving a drive means 5, in this case a pair of endless tracks, to excavate a groove into the bottom of the bed with a water-jet type excavation device 7 which is driven by, for instance, an underwater pump.

The cable 2 is to be buried in the groove. The energy (electric power) and the control signals required for above-mentioned devices are supplied from the mother ship (not shown) through a control cable 4.

Fig. 6 is a schematic view to illustrate that the cable burying apparatus 3 is guided to the cable 2 by using the ultrasonic transmitter/receiver 11 as the cable position confirmation device. The cable is provided with two ultrasonic oscillators 10, and 1 02 in advance.

Since the said ultrasonic oscillators 10, and 102 have transmitters and receivers for ultrasonic, wave signals, they are made to transmit ultrasonic signals when they receive ultrasonic transmission command signals. An ultrasonic signal transmitted from the ultrasonic oscillator 10, can be distinguished from that transmitted from the other oscillator 102 by a simple method, such as, to use the transmission command signals of frequencies different from each other so that respective filters mounted inside the ultrasonic oscillators 10, and 1 02 may discriminate a transmission command to transmit ultrasonic signals from either one of the ultrasonic oscillators 10, and 102.

The ultrasonic transmitter/receiver 11 which is provided on the cable burying apparatus 3 as a cable position confirming device comprises four ultrasonic wave receiving elements 111, to 1114 arranged in a horizontal plane at the corners of a square and an ultrasonic transmitter/receiver element 11 2 located at the centre of the square. When a transmission command in the form of ultrasonic wave signal is transmitted from said ultrasonic transmitter/receiver element 11 2 to either one of the ultrasonic oscillators 10, and 1 02, ultrasonic signals are transmitted in turn from the respective one of the ultrasonic oscillators 10, and 1 02 to be received and processed by the ultrasonic wave receiving elements 111, to 1114 and the ultrasonic trans mitter/receiver element 112, thereby enabling the detection of the position of either one of the ultrasonic oscillators 10, and 1 02 according to the position measurement principle which is explained hereinafter.The information concerning the position is supplied to the mother ship through the control cable 4 to be used as a data for guiding the cable burying apparatus along the cable 2.

Fig. 7 indicates a preferred embodiment of the ultrasonic oscillators 10, and 102 which are mounted on the cable in advance. Fig. (a) is a frontal view and (b) is a cross sectional side view. A support frame 101 of a cylindrical form is mounted on the cable 2 and a rotating member 102 is mounted around the support frame 101 via bearings 103, to 1034 in a freely rotatable fashion. An anchor 104 and a buoy 105 are provided on the rotating member 102 opposite to each other in respect of the cable 2, the anchor 104 extending parallel to the cable 2.

The rotating member 102 is further provided with ultrasonic transmitter/receiver elements 106, and 1062 and an ultrasonic wave absorbing board or an ultrasonic wave diffusing board 107, 108 to avoid the influence of the ultrasonic waves reflected from the bottom. The ultrasonic transmitter/receiver elements 1 06r and 1062 are made to always come above the cable 2 by the anchor 104 and the buoy 105 provided on the rotating member 102. In this embodiment a power source and electric circuits are provided within a buoy to minimize the volumes of the ultrasonic oscillators 10, and 102 mounted on the cable 2.

Fig. 8 schematically explains the principle of calculating the position of the cable used in this embodiment of the present invention. If it is assumed that the velocity of propagation of ultrasonic signals is C and that the time T1 required for the ultrasonic signals to reciprocate between the ultrasonic transmitter/receiver element 11 2 of the ultrasonic transmitter/reciver 11 mounted on the cable burying device 3 and either one of the ultrasonic oscillators 10, and 102 (excluding known time lag caused by a signal processing circuit etc.), the following formula holds for the distance R between the ultrasonic transmitter/receiver element 11 2 and either one of the ultrasonic oscillators 10, and 102;; R = C T1 2 More specifically, the ultrasonic oscillator 10, or 102 is positioned on the surface of the sphere 11 3 having a radius R and having the centre at the position of the ultrasonic transmitter/receiver element 11 2. If it is assumed that a point P is arbitrarily selected within this space, and that the distances between the arbitary point P and the ultrasonic wave re ceiver element 1112 and 1114 are L2 and L4 respectively, a set of the points P collectively expresses a hyperboloid if the difference between L2 and L4, AL( = L2 - L4), is made constant.If the difference in the times re quired for an ultrasonic signal transmitted from either one of the ultrasonic oscillators 10, or 102 to arrive at the ultrasonic receiving element 1112 and to arrive at the other ele ment 1114 is 72, the ultrasonic receiving ele ments 1112 and 1114 being positioned on the diagonal line among elements 111, to 1114, it is obvious that the ultrasonic oscillator 10, or 102 exists on a hyperboloid 114 wherein the above mentioned difference in distance AL has the relation indicated by the formula be low:: AL = C 'T2 2 In a similar method, by measuring the differ ence in times needed for receiving signals by the element 111, and 1113 which are positioned on the diagonal line among other ultra sonic wave receiving elements 111, to 1114, a hyperboloid 115 is obtained. Suppose the intersecting points of a hyperboloid 11 6 which is an overlapping plane made by the hyperboloids 114 and 115 with the sphere 11 3 are 11 7 and 11 8 respectively, the ultra sonic oscillator 10, or 1 02 comes to be posi tioned on the intersection points 11 7 or 11 8.

The intersecting points 11 7 and 11 8 exist at a position symmetrical to the plane by the ultrasonic wave receiving elements 111, to 1114. In the preferred embodiment indicated in Fig. 6, the ultrasonic transmitter/receiver element 11 2 is positioned above the body of the cable burying apparatus 3 and the plane formed by the ultrasonic wave receiving elements 1111 - 1114 is arranged sub stantially parallel to the bottom of the water body; therefore, the intersecting points 11 7 and 11 8 come to be positioned above and under this plane respectively.If the cable 2 is 'laid upon the marine bed and the slope thereon is gradual, the ultrasonic oscillator comes to be positioned on the lower intersect ing point.

Fig. 9 is a block diagram to illustrate an embodiment related to the processing of the signals generated from the ultrasonic transmitter/receiver 11 which is explained in (a) and the ultrasonic oscillator 10, and 102 which is explained in (b).

In (a) when a pulse signal is generated from a pulse generating circuit 11 20 to command transmission of an ultrasonic transmission command signal, a signal is transmitted from a voltage control type oscillator 1121 to be converted into an ultrasonic transmission com mand signal by the ultrasonic transmitter/re ceiver element 11 2. It has been described hereinabove that the frequencies of the transmission command signals in ultrasonic waves to the ultrasonic oscillator 10, and 1 02 are made different from each other in order to discriminate ultrasonic transmission command signal to the ultrasonic transmitter 10, from that of 1 02. Such frequencies can be controlled by controlling the frequency generated from the voltage control type oscillator 1121 by the control circuit 11 22. When an ultrasonic transmission command signal is transmitted from the ultrasonic transmitter/receiver 112, an ultrasonic signal is transmitted in turn from a respective one of the ultrasonic oscillators 10, or 1 02. This return signal is converted into an electric signal by the ultrasonic wave receiving elements 111, to 1114 and the ultrasonic transmitter/receiver element 112, and after it is amplified in amplifier circuits 1123, to 11 235 of narrow band, it is converted into a square wave in waveform shaper circuits 1124, to 11245. Then, time difference measuring circuits 11 2so to 11 253 measure the time T1 needed for reciprocating ultrasonic signals between the ultrasonic transmitter/receiver element 1 12 and either one of the ultrasonic oscillators 10, or 1 02, the difference T2 in times needed for an ultrasonic signal generated from the ultrasonic oscillator 10, or 1 02 to arrive at the ultrasonic receiving elements 11 43 and 11 44, and the difference T3 in times between the ultrasonic wave receiving elements 114, and 11 43. The results are processed in a calculation circuit 11 26 to display the positions of the ultrasonic oscillators 10, and 102 on an indicator 1127.

In (b), on the other hand, a transmission command signal in the form of ultrasonic waves is received by the ultrasonic transmitter/receiver elements 106 and 1062, amplified by a narrow band amplifier circuit 1001 and wave-shaped in a waveform shaper circuit 1002. Signals are further generated from a voltage control type oscillator circuit 1003 so as to be converted into ultrasonic wave signals by the ultrasonic transmitter/receiver elements 106, and 1062.

Fig. 10 is a bottom view to illustrate another embodiment of the ultrasonic transmitter/receiver 11 which may be used as a cable position confirmation device in the present invention. In this embodiment the ultrasonic wave receiving elements 1 11, to 1114 are mounted underneath the lower part of the body of the cable burying apparatus 3 in a rectangular arrangement while the ultrasonic transmitter/receiver element 11 2 is mounted at the centre of the rectangular form. Accordingly, since in this embodiment the elements 1 1 1, to 1114 and 112 can be positioned closer to the ultrasonic oscillators 10, and 102 which have been mounted on the cable 2 in advance, the positions of the ultrasonic oscillators can be calculated with a higher accuracy.The distance between the ultrasonic oscillators 10, and 102 which have been mounted on the cable in advance is made substantially the same to the distance between the ultrasonic wave receiving elements 111, and 1114 or that between 1112and 111 3 which constitute parallel sides. Therefore, by controlling the drive means 5 of the cable burying apparatus 3 so as to position the ultrasonic oscillators 10, and 102 at positions immediately beneath the point bisecting the length of a line connecting the ultrasonic receiving elements 111, to 1112 or 1113 to 1114, the cable burying apparatus can be guided to come directly above the cable 2 and to align the advancing direction thereof with that of the cable 2.

A signal processing system similar to the one shown in the block diagram in Fig. 9 may be used as the signal processing system for the ultrasonic transmitter/receiver elements according to the present invention. Although in the description of the preferred embodiments hereinabove, there has been used the system wherein the ultrasonic oscillators 10, and 102 receive ultrasonic wave transmission command signals and transmit ultrasonic signals, it may be a system wherein ultrasonic signals are transmitted in burst.In such a case, the ultrasonic oscillators 10, and 102 are made to have frequencies different from each other and some of the ultrasonic receiving elements, for instance, 1113 and 1114 are made to correspond to the ultrasonic oscillator 10, while 1112 and 111, are made to correspond to the other ultrasonic oscillator 1 02.

The processing circuit for the received signals comprises circuits respectively assigned to calculate respective time difference.

After the burying apparatus 3 has been made to approach the marine cable 2, the cable 2 has to be engaged with the cable engaging means 9. The procedure to engage the cable 2 within the engaging means 9 is an important operation which could be said as a pre-requisite for moving the burying apparatus 3 precisely along the cable 2 as well as for accurately guiding the cable 2 into the excavated groove in the sea bed. Fig. 11 illustrates an embodiment of the cable engaging means 9. As described hereinbefore, the engaging means 9 has to detect the route of the laid cable 2 in order to travel precisely therealong and therefore, this embodiment is designed to have a mechanism to hold and clamp the cable 2 as well as a mechanism to detect the cable route. The reference numerals 901, 901' denote engaging mechanisms in a semi-cylindrical form which are respectively supported by plates 902 and 902'. The plates 902 and 902' are connected by a spring 903 to force open the engaging mechanisms 901 and 901'. The reference numerals 904 and 904' denote pulleys which are freely rotatable around rotating shafts 905 and 905' in con tact with the plates 902 an 902'. The rotating shafts 905, 905' are connected via arms 906, 906' to a mechanism to detect expansion/compession thereof 907, 907' for instance strain gauges, which are fixed on the middle portion 6 of the burying apparatus 3.

The reference numeral 908 denotes a hinge to connect the plates 902 and 902', 909 a hydraulic cylinder and 910 a piston rod which is reciprocated by the hydraulic cylinder 909.

The hydraulic cylinder 909 is fixed on the mid-line 6 of the burying device 3 while the tip end of the piston rod 910 is connected to the hinge 908. The hydraulic cylinder 909 is driven by a hydraulic unit (not shown).

Figs. 1 2 (a) and (b) illustrate the operation of this embodiment of the cable engaging means 9. The output from the transmitter 10 mounted in advance on the cable 2 is received by the receiver 11 mounted on the apparatus 3, and the apparatus 3 is guided based upon the output from the receiver 11 so that the cable comes between the right and left tracks 5. Under this condition the semicylindrical engaging mechanisms 901 and 901' are kept open by the spring 903. The hydraulic cylinder 909 is operated to compress the piston rod 910 by driving the hydraulic unit (not shown).The plates 902, 902' are pulled by the withdrawal of the piston rod 910 in contact with the pulleys 904, 904' to the direction indicated by the arrow mark in Fig. 1 2 (a), thereby making the semi-cylindrical engaging mechanisms 901, 901' to approach to each other while compressing the spring 903. During such movement, the engaging mechanisms 901 and 901' catch the cable 2 therebetween as illustrated in Fig. 1 2 (b). When the cable 2 is engaged with the engaging mechanism at the centre thereof, the outputs to the right and the left expansion/compression detectors 907, 907' are identical (the difference therebetween is null).When the cable route deviates from the advancing direction of the apparatus 3 either to the right or to the left thereof, the cable 2 engaged with the engaging mechanisms 901, 901' provides a force to push either one of the mechanisms 901 or 901' on the side of the deviation, the force is transmitted through the plate 902, 902', pulley 904 or 904', the rotary shaft 905 or 905', and the arm 906 or 906' which are respectively positioned on the side of the deviation to finally reach the expansion/compression detector 907, 907', thereby detecting the direction of the cable route relative to the apparatus 3. The apparatus 3 can engage the cable 2 with the engaging mechanisms 901, 901' and detect the route of the cable 2 with the expansion/compression mechanisms 907, 907' while travelling along the route by using the tracks 5.Therefore, the apparatus can completely bury the cable underneath the sea bed 1 by operating its excavation means 7 travels along the route while engaging the cable.

In the attached drawings Fig. 1 3 shows the general structure (in a side view) of a further underwater cable burying apparatus according to the present invention wherein reference numerals 3 denotes the apparatus which is made to travel on the sea bed by driving endless tracks 5. At the front end of the burying apparatus extends on arm 1 2 which is provided with a cable clamp member 9 to catch a cable 2 and a cable engaging member 1 3. An excavation device for water jet type 7 is provided at the middle portion of the burying device. The electric energy (power) required for said devices 9, 1 3 and 7, and the travelling device 5 etc. and control signals therefor are supplied from the mother ship (not shown) via the control cable 4.The reference numeral 1 4 denoted an underwater TV camera.

The operation is conducted according to the following procedure.

The position of the cable 2 which is laid on the sea bed is confirmed through the underwater TV camera 14 aboard the mother ship in this embodiment. With the aid of the information thus obtained, the burying apparatus 3 can approach close to the cable 2 by using its tracks 5 while simultaneously advancing toward the direction indicated by the arrow mark to catch the cable 2 with the cable clamp member 9. Then the cable is passed through the cable engaging member 1 3 and at the same time the apparatus crushes or displaces sand and dirt upon the sea bed by using the water jet nozzle provided at the tip end of the excavation device to make grooves as well as placing and burying the cable 2 therein.

Fig. 14 shows an embodiment of the cable clamp member 9 of the apparatus according to the present invention. Fig. 14 (a) is a frontal view and Fig. 14(b) is a side view thereof. The cable 2 (not shown in Fig. 14) is caught in an embracing manner from both sides by the semi-cylindrical claws 90, and 902. The claws 90, and 902 are made to open/close around a fulcrum 92 fixed on the supporting frame 91. The claws 90, and 902 are provided with rods 94, and 942 through fulcrums 93, and 932 which are freely rotatable. The rods 94, and 942 are connected to a sliding member 96, which is slidable by the revolution of gear 95, through the freely rotatable fulcrum 933. The sliding member is driven by a motor 97, fixed upon the support frame 91 via gears 952 and 953.In other words, the sliding member 96, is slid vertically through the action of gears 953, 952 and 95, when the motor 97, revolves thereby opening/closing the claws 90, and 902 via the rods 94, and 942 The upper portion of the support frame 91 is supported by the arm 1 2 which extends forward from the burying device 3 and is slid vertically by the rotation of a motor 972 and a gear 954 which is interlocked thereto. Accordingly the support frame 91 is moved upward and downward by the rotation of the motor 972 fixed on the arm 12, thereby simultaneously moving upward and downward the cable clamp claws 90, and 902 provided on the support frame 91.The rotation of the motors 97 and 977 is controlled from the mother ship through the control cable 4 connecting the mother ship to the apparatus 3.

The operational procedure to clamp the cable 2 will now be explained referring to Fig.

1 5. Based upon the information from the underwater TV camera 1 4 mounted in the apparatus 3, the tracks 5 are controlled so as to locate the cable clamp member 9 at a position immediately above the cable 2. (Refer to (a).) Then the gear 964 is rotated by driving the motor 972 as explained above referring to Fig. 14 to lower the cable clamp claws 90, and 902 downward toward the cable 2 (Refer to Fig. (b)). The sliding member 961 is slid downward by driving the motor 97, via the gears 952, 952 and 95 so that the claws 90, and 902 can clamp and catch the cable 2 (Refer to Fig. (c)).By driving the gear 954, the cable clamp claws 90, and 902 are raised upward to complete the catching operation (Refer to Fig. (d)).

Fig. 1 6 shows another embodiment of a cable clamp member for use in apparatus according to the present invention wherein Fig. (a) is a frontal view and Fig. (b) a side view to illustrate the condition where it has caught the cable 2. In this embodiment as is the case indicated in Fig. 14, the cable 2 is held in an embracing manner by the cable clamp claws 901 and 902 from both sides.

The lower sides of the claws are shaped as substantially horizontal plates and the caught cable 2 is laterally movable between the two claws 90 and 90,. In the embodiment, therefore, the tracks 5 can be controlled so as to move the apparatus 3 along the cable 2 by measuring the lateral displacement of the cable 2 and by assuming the direction to lay the cable 2.

The lateral displacement of the cable 2 can be detected by using the fact that the lateral displacement of the cable 2 makes a press board 98 or 987 provided in the claws 90, and 902 slide either to the right or to the left so as to rotate a potentiometer 99 through a gear 95, or 95,. More specifically, the press boards 98 and 987 are made to locate close to the central points of the claws 90, and 902 which comprise the clamping member for the cable 2 when they are not pressed by the cable 2.The rotational angle of the potentiometers 99 and 997 is, therefore, determined by the amount of lateral displacement of the cable 2 and the displacement is readily converted to electric signals. The electric signals which express the lateral displacement of the cable 2 are transmitted to the mother ship via the control cable 4 to be used as the data for controlling the drive means of the apparatus 3.

Since the operational procedure to catch and clamp the cable in this embodiment is similar to that explained in respect of Fig. 14, and the identical parts of the members are denoted with identical reference numerals in both figures, further explanation is unnecessary.

Fig. 1 7 indicates an embodiment of the cable engaging member 1 3 of burying apparatus 3 according to the present invention wherein Fig. (a) is a frontal view while Fig. (b) a bottom view thereof. A slidable member 131 is engaged with and slidable across an arm 1 2 which projects forward from the apparatus 3. Member 131 is made freely slidable in a horizontal transverse direction by the action of a driving gear 1 32. When the slidable member 131 is slid to the left by the driving gear 132, a void space is created at the position indicated by the arrow mark in Fig. 1 7 (a). Into this space is directed cable 2 which has been caught by a cable catching member 9 (not shown).The cable 2 is directed in from beneath the sliding member 131 and is inserted into place between a roller 135, provided on the arm 1 2 and a roller 1352 provided on the sliding member 1 31. On the side of the arm 1 2, on the other hand, there are provided a driving motor 1 33 and transmission gears 134, and 1342. The cable 2 is made to be rolled in or out of the cable engaging member 1 3 by the rotation of the roller 135, which is interlocked with the rotation of the transmission gears 134, and 1342 which are driven to rotate by the driving motor 1 33. The cable 2 is effectively fed into the groove formed by the excavation member 7 by this roll-in/roll-out mechanism. The revolution of the driving gear 133, too, is controlled through the control cable 4 aboard the mother ship.

As described hereinabove, the present invention can solve problematic matters conventionally considered impossible or extremely difficult and enables the device to bury a cable under the sea bed accurately as well as effectively under any conditions, attaining a remarkable achievement.

Claims

1. Apparatus for burying an underwater cable in the bed of a body of water, comprising means for locating a cable laid on said bed, means for involving the vehicle over said bed, means for engaging the cable and means for progressively burying the cable.

2. Apparatus as claimed in claim 1 wherein the means for locating the cable constitutes a television camera.

3. Apparatus as claimed in claim 1 wherein said means for locating the cable comprises one or more detectors for receiving a signal emitted from the cable location.

4. Apparatus as claimed in claim 3 wherein the detector or detectors are for receiving ultrasonic sound signals.

5. Apparatus as claimed in claim 3 or claim 4 comprising a transmitter for sending a command signal to a receiver/transmitter at the cable location which on receiving the command signal is caused to transmit.

6. Apparatus as claimed in claim 4 or claim 5 comprising an array of receivers for ultrasound located at the four carriers of a horizontal rectangle and a receiver/transmitter for ultrasound located at the crossing of the diagonal of the rectangle.

7. Apparatus as claimed in claim 6 wherein the rectangle is a square.

8. Apparatus as claimed in any preceding claims further comprising means for detecting the route of a cable engaged in said cable engaging means.

9. Apparatus as claimed in claim 8 wherein the means for engaging the cable comprises a pair of opposed claws which are closeable over the cable when the apparatus is oriented to travel generally along the cable route and wherein the means for detecting the route of the cable comprises means for running the lateral movement of the cable in the claws as the apparatus is driven along the said route.

10. Apparatus for burying an underwater cable substantially as hereinbefore described with reference to as as illustrated in Figs. 2 to 4, 5 to 12 or 13 to 17 of the accompanying drawings.

11. A method for burying an underwater cable laid on the bed of a body of water using apparatus as claimed in any preceding claim which method comprises locating the cable by the cable locating means of the apparatus bringing the apparatus to the cable and engaging the cable in the cable engaging means of the apparatus and causing the apparatus to progress along the route of the cable progressively burying the cable.

1 2. A method as claimed in claim 11 wherein the cable and the apparatus are each provided with one or more ultrasound transmitter/receivers, and comprising transmitting a command signal from the apparatus to cause a homing signal to be emitted from the cable, and receiving said homing signal at the apparatus and locating the cable therefrom.

1 3. A method for burying an underwater cable substantially as herein before described with reference to Figs. 2 to 4, 5 to 1 2 or 1 3 to 1 7 of the accompanying drawings.

14. An ultrasonic oscillator to be mounted on a cable to enable the cable to be subsequently located which comprises a support frame mounted on the outer periphery of the cable, and a rotatable member mounted on said support frame in a freely rotatable fashion which rotatable member is provided with an ultrasound receiving element.

15. An ultrasonic oscillator as claimed in claim 14 comprising an anchor and a buoy provided on the rotating member on opposite sides thereof with respect to the cable.

1 6. An ultrasonic oscillator substantially as herein before described with reference to and as illustrated in Fig. 7 of the accompanying drawings.

1 7. A marine cable burying method which is characterized in that an output transmitted from a transmitter mounted on a cable in advance is received by a receiver provided on a burying device to control a travelling control mechanism so that said burying device is guided to approach said cable by a travelling means, that said burying device catches and engages said cable with a cable engaging means and that the burying device travels along the cable route which has been formed by said travelling means and by detecting the route of said cable.

18. A marine cable burying method as claimed in claim 1 7 characterized in that a transmission command signal in ultrasonic waves transmitted from an ultrasonic transmitter/receiver mounted on the cable burying device is received by an ultrasonic oscillator mounted on the cable in advance, that an ultrasonic signal is transmitted by said ultra; sonic oscillator in turn to be received by said ultrasonic transmitter/receiver, and that signals are processed to detect the position of said ultrasonic oscillator mounted upon the cable.

1 9. A marine cable burying method as claimed in claims 1 7 or 1 8 which is characterized in that the position of said ultrasonic oscillator upon the cable is detected by obtaining the over-lapping plane of the hyperboloids which can be obtained by measuring the time required for reciprocating an ultrasonic signal between the ultrasonic transmitter/receiver element of the ultrasonic transmitter/ receiver and the ultrasonic oscillator and the difference in times required for the ultrasonic signal transmitted from said ultrasonic oscillator to arrive at either one of the two sets of two ultrasonic receiving elements which are crossing each other among the four ultrasonic receiving elements of said ultrasonic transom'it ter/receiver and for the signal to arrive at the other element of the set.

20. A marine cable burying device which is characterized in that a receiver to receive an output transmitted from a transmitter mounted on a cable in advance and a travelling means which is controlled by the output from the receiver are provided and that a cable engaging means having a cable engaging mechanism and a cable route detecting mechanism and an excavation means are provided on said device body at the middle portion thereof.

21. A marine cable burying device as claimed in claim 20 characterized in that said cable clamp member comprises two semicylindrical claws which are fixed on a support frame support by the arm at the upper portion thereof and which are made to open/close around a fulcrum by sliding a sliding member vertically.

22. A marine burying device as claimed in claims 20 or 21 which is characterized in that the claws in said cable clamp device are formed horizontally at the lower side thereof, that press boards are provided above said claws through springs, and that a potentiometer is rotated by lateral sliding movement of said press board.

23. A marine cable burying device as claimed in claim 20 characterized in that the arm in said cable engaging member is engaged with a sliding member which is horizontally displaceable and that the cable is made to be inserted between a roller provided on said arm and a roller which is interlocked with the revolution of a driving motor.

24. A cable position confirming device for apparatus for burying an underwater cable device comprises four ultrasonic receiving elements are provided on the cable burying apparatus at the corners of a horizontal rectangle and an ultrasonic transmitter/receiver element provided at the centre of the square.

25. A cable position confirming device as claimed in claim 24 wherein the rectangle is a square.

26. A cable position confirming device for a marine cable burying device as claimed in claim 24 which is characterized in that the four ultrasonic receiving elements are arranged in the form of a rectangle with an ultrasonic transmitter/receiver element is provided at the centre of the rectangular form, that the distance between two ultrasonic oscillators mounted on the cable in advance is made to be substantially identical to the distance between said ultrasonic receiving elements forming parallel sides of the rectangle and that said respective elements are provided beneath the cable burying device.