Patent Publication Number: US-10781656-B2

Title: Undersea mining base, mining base monitoring device, and chimney avoidance method for seabed deposit

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2016-163682, filed Aug. 24, 2016, which is herein incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a technology for mining seabed minerals. 
     BACKGROUND 
     Recent years have seen rising prices of useful metals, which are those essential to manufacture various kinds of industrial equipment but abundance thereof is lacking. Useful metals are essential in industry, but there are small amounts of them that can be mined, as well as the number of producing countries is limited, so that geopolitical risks are present. Then, among seabed minerals, useful metal-containing minerals present under the seabed are drawing attention. 
     Various investigations have shown that seabed minerals contain useful metals at higher concentrations, as compared with minerals currently mined on ground. Accordingly, in the recent years, various institutions have conducted trial mining and investigations, and also, various methods and systems for mining seabed minerals have been proposed (e.g., see JP 2013-528726 A). 
     JP 2013-528726 A discloses a seabed mineral mining system. The mining system disclosed in the literature includes a seabed locomotion device having a cutting tool capable of cutting a surface of a seabed ore deposit. While receiving power and control signals from a supply source on a sea level side and traversing the seabed, the seabed locomotion device cuts the surface of a seabed ore deposit by an open-type cutting tool. Cuttings produced by the cutting are sized by sizing means to ensure that such cuttings are no greater than a predetermined size, and the sized cuttings are transported up to the sea level. 
     BRIEF SUMMARY 
     However, in the technology disclosed in JP 2013-528726 A, a crawler-type cutting machine has a problem where operation corresponding with seabed unevenness is complicated, which makes automation difficult. In addition, on seabed ore deposits, there are seamounts with large slope angles, which are obstacles to a crawler traveling on soft ground accumulated on the surfaces thereof. 
     Accordingly, the present invention has been accomplished focusing on such problems. It is an object of the present invention to provide an undersea mining base capable of corresponding with slopes and undulations of seabed ore deposits, a mining base monitoring device, and a method for avoiding chimneys of seabed ore deposits. 
     In order to achieve the object mentioned above, according to an aspect of the present invention, there is provided an undersea mining base arranged undersea and erected on a seabed, the undersea mining base mining seabed minerals while forming a bottomed hole in a seabed ore deposit, and collecting the mined seabed minerals from an inside of the bottomed hole, the undersea mining base including: a seabed mineral mining device configured to form the bottomed hole in the seabed ore deposit and a platform equipped with the seabed mineral mining device; wherein the platform includes a plurality of support legs, each of the support legs being configured to be individually relatively slidable in a Z direction via a vertical movement mechanism. 
     In the undersea mining base according to the one aspect of the present invention, the platform erected on the seabed is equipped with the seabed mineral mining device, and includes the plurality of support legs. Each support leg is configured to be individually relatively slidable in the Z direction via the vertical movement mechanism, thus enabling the undersea mining base to correspond with slopes and undulations of seabed ore deposits. 
     In addition, in order to achieve the object mentioned above, according to another aspect of the present invention, there is provided an undersea mining base arranged undersea and erected on a seabed, the undersea mining base mining seabed minerals while forming a bottomed hole in a seabed ore deposit, and collecting the mined seabed minerals from an inside of the bottomed hole, the undersea mining base including: a seabed mineral mining device configured to form the bottomed hole in the seabed ore deposit and a platform equipped with the seabed mineral mining device and self-movable in at least one of an X direction and a Y direction orthogonal to each other in a horizontal plane. 
     In the undersea mining base according to the other aspect of the present invention, the platform erected on the seabed is equipped with the seabed mineral mining device, and is movable by itself in at least one of the X and Y directions, thus enabling the undersea mining base to correspond with the slopes and undulations of seabed ore deposits. 
     Herein, in the undersea mining base according to the other aspect of the present invention, preferably, the platform includes an upper platform, a lower platform, and a middle frame arranged between the upper and lower platforms, in which the middle frame and the upper platform are configured to be relatively slidable in one direction via a horizontal movement mechanism, the middle frame and the lower platform are configured to be relatively slidable in an other direction orthogonal to the one direction via a horizontal movement mechanism, and each of the upper and lower platforms includes a plurality of support legs, each of the support legs being configured to be individually relatively slidable in a Z direction via a vertical movement mechanism. The structure thus formed is suitable to correspond with the slopes and undulations of seabed ore deposits. 
     Additionally, preferably, the undersea mining base according to any one of the aspects of the present invention further includes chimney detection means configured to detect at least one chimney on the seabed ore deposit. The structure thus formed enables chimney detection on seabed ore deposits, and therefore is more suitable to correspond with the slopes and undulations of the seabed ore deposits. 
     Furthermore, to solve the above problems, a mining base monitoring device according to one aspect of the present invention is a mining base monitoring device equipped in an offshore base or a land base to monitor the undersea mining base according to any one of the aspects of the present invention, and is characterized by including chimney monitoring means configured to monitor the chimney of the seabed ore deposit. 
     In the mining base monitoring device according to the one aspect of the present invention, when an operator monitors an undersea mining base in the offshore base or the land base, he or she can monitor chimneys on a seabed ore deposit in the offshore base or the land base, so that it is possible to correspond with the slopes and undulations of the seabed ore deposit. 
     In addition, in order to achieve the object mentioned above, according to still another aspect of the present invention, there is provided a method for avoiding a chimney on a seabed ore deposit, which is a method for avoiding interference between a work device used on a seabed ore deposit and configured to perform work necessary to mine while self-travelling on a seabed and a chimney on the seabed ore deposit, the method including: detecting the chimney on the seabed ore deposit on a basis of an echo obtained by underwater detection through transmission and reception of an ultrasonic wave; and avoiding the interference between the work device and the chimney on a basis of position information of the chimney obtained at the detecting. 
     In the method for avoiding a chimney on a seabed ore deposit according to the one aspect of the present invention, the chimney on the seabed ore deposit is detected on the basis of the echo obtained by underwater detection through transmission and reception of an ultrasonic wave, and interference between a work device and the chimney is avoided on the basis of the position information of the chimney obtained at the chimney detection step, so that it is possible to correspond with the slopes and undulations of the seabed ore deposit. 
     As mentioned above, according to the present invention, it is possible to correspond with the slopes and undulations of the seabed ore deposit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating one embodiment of the entire structure of a seabed mineral mining system according to one aspect of the present invention. 
         FIGS. 2A and 2B  are schematic illustrative diagrams of an undersea mining base of the mining system of  FIG. 1 , in which  FIG. 2A  is a plan view, and  FIG. 2B  is a front view of an undersea mining base (in which the part of a seabed ore deposit depicts a cross-sectional image (hereinafter the same in front view)), which are each schematically represented. 
         FIG. 3  is a schematic perspective diagram illustrating a first embodiment of the undersea mining base of  FIGS. 2A and 2B . 
         FIG. 4  is a schematic front view illustrating a seabed mineral mining device equipped in the undersea mining base. 
         FIG. 5  is an illustrative diagram (a hammer advanced state) of a mining device main body of the seabed mineral mining device of  FIG. 4 , the diagram illustrating a longitudinal cross-section including an axis line. 
         FIG. 6  is an illustrative diagram (a hammer retracted state) of the mining device main body of the seabed mineral mining device of  FIG. 4 , the diagram illustrating a longitudinal cross-section including an axis line. 
         FIGS. 7A and 7B  are illustrative diagrams of a seabed mineral mining method by the mining system of  FIG. 1 , in which  FIG. 7A  is a front view of an undersea mining base, and  FIG. 7B  is a plan view of one section of a seabed ore deposit, which are each schematically represented. 
         FIGS. 8A and 8B  are illustrative diagrams of a seabed mineral mining method by the mining system of  FIG. 1 , in which  FIG. 8A  is a front view of an undersea mining base, and  FIG. 8B  is a plan view of one section of a seabed ore deposit, which are each schematically represented. 
         FIG. 9  is a longitudinal cross-sectional diagram of a modification of a seabed mineral mining device according to one aspect of the present invention. 
         FIGS. 10A to 10C  are schematic plan views of a second embodiment of an undersea mining base according to one aspect of the present invention. 
         FIG. 11  is a schematic perspective diagram illustrating a third embodiment of the undersea mining base according to the one aspect of the present invention. 
         FIG. 12  is a schematic plan view of a platform of the undersea mining base of the third embodiment. 
         FIG. 13  is a schematic front view of the platform of the undersea mining base of the third embodiment. 
         FIG. 14  is a schematic plan view of a middle frame of the undersea mining base of the third embodiment. 
         FIG. 15  is a transverse cross-sectional diagram of a support leg of the undersea mining base of the third embodiment. 
         FIG. 16  is a cross-sectional diagram taken along line R-R of  FIG. 12 . 
         FIG. 17  is a cross-sectional diagram taken along line S-S of  FIG. 12 . 
         FIG. 18  is a cross-sectional diagram taken along line P-P of  FIG. 12 . 
         FIG. 19  is a cross-sectional diagram taken along line Q-Q of  FIG. 12 . 
         FIG. 20  is a diagram illustrating an image of one example of relative dimensions of the undersea mining base of the third embodiment and a seabed ore deposit (including a chimney). 
         FIGS. 21A and 21B  are diagrams illustrating one embodiment of a bottom landing method for the undersea mining base in the mining system of the present invention. 
         FIGS. 22A to 22D  are diagrams illustrating one embodiment of the bottom landing method for the undersea mining base in the mining system of the present invention. 
         FIG. 23  is a diagram illustrating steps of mining a seabed ore deposit by the undersea mining base of the third embodiment. 
         FIG. 24  is a diagram illustrating a walking motion (a transitional motion from a bottom landing preparation posture to a mining start posture) of the platform of the undersea mining base in the mining steps of  FIG. 23 . 
         FIGS. 25A to 25D  are perspective diagrams illustrating a walking motion of the undersea mining base of the third embodiment. 
         FIG. 26  is an enlarged view of  FIG. 25A . 
         FIG. 27  is an enlarged view of  FIG. 25B . 
         FIG. 28  is an enlarged view of  FIG. 25C . 
         FIG. 29  is an enlarged view of  FIG. 25D . 
         FIG. 30  is a diagram ((a) to (c)) illustrating a walking motion of the platform of the undersea mining base in the mining steps of  FIG. 23 . 
         FIG. 31  is a diagram ((a) to (f)) illustrating a walking motion of the platform of the undersea mining base in the mining steps of  FIG. 23 . 
         FIG. 32  is a diagram ((a) to (c)) illustrating a walking motion of the platform of the undersea mining base in the mining steps of  FIG. 23 . 
         FIG. 33  is a diagram ((a) to (c)) illustrating a walking motion of the platform of the undersea mining base in the mining steps of  FIG. 23 . 
         FIGS. 34A to 34C  are diagrams illustrating one embodiment of an erection and installation mother ship for use in the mining system of the present invention, in which  FIG. 34A  is a plan view,  FIG. 34B  is a front view, and  FIG. 34C  is a right side view. 
         FIG. 35  is a block diagram illustrating a base control unit in the third embodiment. 
         FIG. 36  is a flowchart of chimney avoidance processing to be executed by the base control unit illustrated in  FIG. 35 . 
         FIG. 37  is a block diagram illustrating a mining base monitoring device in the third embodiment. 
         FIG. 38  is a flowchart of mining base monitoring processing to be executed by the mining base monitoring device illustrated in  FIG. 37 . 
         FIGS. 39A and 39B  are diagrams illustrating a chimney avoidance motion in the third embodiment, in which the diagrams correspond to the state of moving steps illustrated in  FIG. 30 . 
         FIGS. 40A and 40B  are diagrams illustrating a chimney avoidance motion in the third embodiment, in which the diagrams correspond to the state of moving steps illustrated in  FIG. 30 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. However, the drawings are schematic. Therefore, it should be noted that a relation and ratio between thickness and planar dimensions, and the like are different from actual ones, and portions where dimensional relations and ratios are different from one another among the drawings are also included. In addition, the embodiment, which will be described below, exemplify a device and method to embody a technical idea of the present invention, and the technical idea of the present invention does not limit materials, shapes, structures, arrangements, and the like of the constituent components to those described in the embodiments below. 
     First, a description will be given of the entire structure of a mining system of the present embodiment. 
     As illustrated in  FIG. 1 , the mining system includes a mining mother ship  1  that is placed as an offshore mining base on a sea level SL, a mining station  20 , and a mineral lifting unit  4  that are placed on a seabed SB. In the mining system, a plurality of mining stations  20  are used as undersea mining bases. Each mining station  20  is equipped with a plurality of seabed mineral mining devices  30  (hereinafter also referred to as “mining devices  30 ”). 
     Each mining device  30  is configured to be capable of forming a pit that is a bottomed hole in a seabed ore deposit OD by drilling. Additionally, each mining device  30  is configured to be capable of mining by forming seabed minerals into a slurry in the pit. Then, the mining system transfers the slurry of the seabed minerals mined by each mining device  30  to the undersea mineral lifting unit  4  via a suction pipe  5 . The mineral lifting unit  4  is configured to lift the minerals up to the mining mother ship  1  via a mineral lifting pipe  6 . 
     Specifically, in an example of the present embodiment, the mining mother ship  1 , an erection and installation mother ship  2 , and a carrier ship  3  are anchored at the sea level SL in a target sea region. The erection and installation mother ship  2  is a mother ship for erection and installation configured to carry the mineral lifting unit  4  and the plurality of mining stations  20  and erect and install them on the seabed SB. The erection and installation mother ship  2  is equipped with a work machine  11  such as a crane or the like for erecting and installing the mineral lifting unit  4  and the mining stations  20  on the seabed SB. The erection and installation mother ship  2  carries the mining stations  20  to a predetermined position on the seabed ore deposit OD, and hangs down the mining stations  20  with a winch  11   w  of the work machine  11  to erect them on the seabed SB. Additionally, similarly, the erection and installation mother ship  2  installs the mineral lifting unit  4  at an appropriate position on the seabed SB. 
     The mining mother ship  1  is mounted with a power generator  12  and a reservoir  13 , as well as an unillustrated management computer. The reservoir  13  is replaceably mounted on the ship. The management computer and the power generator  12  are connected to the mining stations  20  and the mineral lifting unit  4  installed on the seabed SB via an umbilical cable  8  to enable supply of electrical power and control signals necessary to operate the mining stations  20  and the mining devices  30 , as well as the mineral lifting unit  4 . 
     The mineral lifting unit  4  includes a mineral lifting pump  25  and a sizer  27  with a cyclone device. A discharge side of the sizer  27  is connected to a suction side of the mineral lifting pump  25  in the mineral lifting unit  4 . A suction side of the sizer  27  is connected to each mining station  20  via the suction pipe  5 . Sea water is filled in the suction pipe  5 . One end of a discharge pipe  7  is connected to the sizer  27 , and the other end of the discharge pipe  7  is piped to a place for returning and leaving minerals determined to be unnecessary by sizing. Note that flexible pipes are used for the suction pipe  5 , the mineral lifting pipe  6 , and the discharge pipe  7 . 
     The mineral lifting pump  25  is connected to the mining mother ship  1  via the mineral lifting pipe  6 . The mineral lifting pipe  6  is a cylindrical pipeline having flexible properties for lifting the slurry of the seabed minerals mined by each mining station  20  up to the mining mother ship  1 . Sea water is filled in the mineral lifting pipe  6 . An upper portion of the mineral lifting pipe  6  reaches the mining mother ship  1  on the sea level SL, and is connected to the reservoir  13  via a ship bottom of the mining mother ship  1 . The reservoir  13  stores the mineral slurry lifted up from the mineral lifting pipe  6  by the mineral lifting pump  25 . The carrier ship  3  replaces the reservoir  13  with that of the mining mother ship  1 , and transfers the seabed mineral lifted to the mining mother ship  1  to a necessary place. 
     Next, the mining stations  20  will be described in detail. As illustrated in  FIGS. 2A and 2B , each mining station  20  includes a rectangular frame-shaped base frame  21  configured to serve as a platform. The base frame  21  is supported by a plurality of (four in this example) support legs  26  at four corners of the frame. Each support leg  26  is fixed to the base frame  21  via a jack mechanism  49 . 
     The jack mechanism  49  includes a motor, a deceleration mechanism, and a rack and pinion mechanism, which are unillustrated. The rack is formed along an axial direction of each support leg  26 . The jack mechanism  49  drives the rack and pinion mechanism by the motor via the deceleration mechanism to be able to slide the support leg  26  in a vertical direction (a Z direction) and maintain a position to which the support leg  26  has been moved. Note that the motor for driving the jack mechanism  49  may be driven by fluid pressure (e.g., hydraulically driven) or driven by electrical power (e.g., an electromagnetic motor) (hereinafter the same in other driving motors). 
     In this example, as illustrated in  FIG. 3 , two movement frames  43  are stretched across the base frame  21  along an X direction. The movement frames  43  have, for example, a truss structure. Both ends of each movement frame  43  are supported on the base frame  21  via a Y-direction movement mechanism  44 . The Y-direction movement mechanism  44  includes a motor, a deceleration mechanism, and a rack and pinion mechanism, which are unillustrated, and drives the rack and pinion mechanism by the motor via the deceleration mechanism to be able to slide the movement frame  43  in the Y direction along the base frame  21 . 
     In each movement frame  43 , a guide shell  48  is longitudinally arranged. Each guide shell  48  forms a feeding mechanism for each mining device  30  in the Z direction. The guide shell  48  is supported on the movement frame  43  via an X-direction movement mechanism  52 . The X-direction movement mechanism  52  includes a motor, a deceleration mechanism, and a rack and pinion mechanism, which are unillustrated, and drives the rack and pinion mechanism by the motor via the deceleration mechanism to be able to slide the guide shell  48  in the X direction along the movement frame  43 . 
     Furthermore, the base frame  21  includes a base control unit  45  and a suction chamber  51 . The umbilical cable  8  is connected to the base control unit  45 . To drive the mining station  20  and the mining device  30 , the base control unit  45  incorporates a high pressure water supply pump, a motor for driving the high pressure water supply pump, and a control unit configured to control operation of the entire mining station  20 , which are unillustrated. 
     This allows each mining station  20  to receive, in the base control unit  45 , necessary electrical power and control signals supplied from the mining mother ship  1  via the umbilical cable  8 . The base control unit  45  serves as a controller configured to control the posture of each mining station  20  by driving of each jack mechanism  49  on the basis of a command of the management computer on the mining mother ship  1  side. 
     Furthermore, each mining station  20  can move the guide shell  48  in the X direction and the Y direction by driving of the X-direction movement mechanism  52  and the Y-direction movement mechanism  44  by the base control unit  45 , and can supply sea water taken in, as high pressure water, to each mining device  30  by driving of the high pressure water supply pump to drive each mining device  30  provided on the guide shell  48 , under management of the management computer. 
     Next, the mining devices  30  equipped in each mining station  20  will be described in detail. 
     As illustrated in  FIG. 4 , each guide shell  48  is equipped with the mining device  30  via a slider  46 . At an upper portion of the guide shell  48  is provided a slide movement mechanism  47  configured to slide the slider  46  in the Z direction along the guide shell  48 . The slide movement mechanism  47  includes a motor, a deceleration mechanism, and a rack and pinion mechanism, which are not unillustrated, and drives the rack and pinion mechanism by the motor via the deceleration mechanism to be able to slide the slider  46  in the Z direction along the guide shell  48 . 
     Each mining device  30  includes a housing unit  71  attached to the slider  46 . The housing unit  71  incorporates a rotating drive mechanism and a swivel, which are unillustrated. In the housing unit  71 , an upper portion of the housing unit  71  is connected to the high pressure water supply pump of the base control unit  45  via a high pressure water supply pipe  9 . Additionally, to a side face of the housing unit  71  is connected one end of the suction pipe  5  for suctioning the slurry of minerals mined by driving of the mining device  30 . The other end of the suction pipe  5  is connected to the sizer  27  via the suction chamber  51 . 
     Next, the structure of a mining device main body of the mining device  30  will be described in more detail. 
     As illustrated in  FIG. 5  by enlarging the mining device main body, the mining device  30  is equipped with a mining device main body  10  at a portion ahead of a double pipe rod  40 . The mining device main body  10  includes a cylindrical cylinder  31 . A substantially cylindrical cylinder liner  33  is fitted into an inner peripheral surface of the cylinder  31 . Between the cylinder  31  and the cylinder liner  33  is formed a water passage hole  32  along an axial direction of the cylinder  31 . 
     A substantially cylindrical hammer  34  is held in the cylinder liner  33  in such a manner as to be reciprocally slidable. A rear end of the cylinder  31  is connected to the double pipe rod  40  of the mining device  30  via a connection member  35 . The double pipe rod  40  is formed by a double pipe including an outer cylinder  40   a  and an inner cylinder  40   b  coaxially. A water supply passage  40   c  is formed in a gap between the outer cylinder  40   a  and the inner cylinder  40   b . An upstream side of the water supply passage  40   c  is connected to the high pressure water supply pipe  9  via the swivel of the housing unit  71 . The high pressure water supply pipe  9  is connected to a discharge side of the high pressure water supply pump provided in the base control unit  45  of the mining station  20 . A downstream side of the water supply passage  40   c  is communicating with a water supply passage  35   c  in the connection member  35 . 
     A cylinder bush  36  is inserted between the rear end of the cylinder  31  and a front end face of the connection member  35 . In a front side of the cylinder bush  36  is inserted a ring  39  for forming a cylinder rear chamber  42 . By doing this, the cylinder rear chamber  42  is defined between the ring  39  and a rear portion of the hammer  34 . In the cylinder bush  36  is provided a communication hole  36   c  communicating with the water supply passage  35   c  along the axial direction. 
     A bit  50 , which is a crushing tool for striking, is attached to a front end of the cylinder  31 . A cylinder front chamber  41  is defined between a rear end of the bit  50  and a front part of the hammer  34 . The bit  50  covers a front side face of the cylinder front chamber  41 , and is attached such that a rear end of its own receives a striking force from the hammer  34  so as to be reciprocally slidable at a predetermined stroke in the axial direction. On an outer peripheral surface of the hammer  34  are formed a plurality of control grooves  34   a  and  34   c  and a communication flow passage  34   b.    
     In the cylinder  31 , a first water inlet hole  31   b  is formed between the front side of the cylinder bush  36  and the ring  39 . The first water inlet hole  31   b  allows the communication hole  36   c  of the cylinder bush  36  and a communication hole  33   e  of a rear end of the cylinder liner  33  to communicate with each other. The communication hole  33   e  of the cylinder liner  33  is communicating with the water passage hole  32 . The water passage hole  32  allows the control grooves  34   a  and  34   c  of the hammer  34  to communicate with a plurality of communication holes  33   a  to  33   d  of the cylinder liner  33  at predetermined positions in accordance with a position of the hammer  34  in the axial direction to form a hammer reciprocation switch mechanism for supplying and discharging high pressure water to and from the cylinder front chamber  41  or the cylinder rear chamber  42  so as to move the hammer  34  forward and backward in the cylinder  31 . 
     Furthermore, in the cylinder  31 , a cylindrical sleeve  38  is provided coaxially with the cylinder  31 . Inside the sleeve  38 , a suction hole  38   t  is penetratingly formed along the axial direction. The sleeve  38  holds a position in the axial direction by a stepped portion formed at a rear portion thereof and inserted into the cylinder bush  36  and the ring  39 . A rear end of the suction hole  38   t  of the sleeve  38  communicates with a front end of the suction hole  40   t  of the inner cylinder  40   b  of the double pipe rod  40  via the suction hole  35   t  of the connection member  35 . 
     An intermediate portion of the sleeve  38  is inserted through a communication hole  34   d  penetratingly formed in the hammer  34  via a gap, and a front end of the sleeve  38  is inserted in a communication hole  50   d  penetratingly formed in the bit  50 , via a gap. In the sleeve  38 , gap portions in a radial direction inserted in the hammer  34  and the bit  50  form a drainage passage  38   a  from the cylinder front chamber  41  and the cylinder rear chamber  42 . 
     In the sleeve  38 , a discharge hole  38   g  is formed at a position on a leading end side of the drainage passage  38   a . The discharge hole  38   g  is inclined toward the suction hole  38   t  at the center of the sleeve  38  from an outer periphery thereof, and also rearwardly toward the direction of the double pipe rod  40 . In the suction hole  38   t  of the sleeve  38 , a flexible check valve  37  is installed at an outlet of the discharge hole  38   g  to prevent earth and sand, or the like from entering the cylinder front chamber  41 . 
     At a front end of the bit  50 , a water suction hole  50   k  is opened that communicates with the suction hole  38   t  at the center of the sleeve  38 . In this manner, in the mining device  30 , flow velocity of high pressure water discharged rearwardly from the discharge hole  38   g  toward the suction hole  38   t  produces negative pressure in the water suction hole  50   k , whereby the seabed mineral suctioned from the water suction hole  50   k  is mixed with sea water in the suction hole  38   t.    
     Accordingly, in the mining device  30 , seabed minerals crushed by drilling are suctioned into the mining device  30  by a drainage flow and mixed with the sea water in the suction hole  38   t  to be able to produce a slurry. Additionally, in the mining device  30 , the produced slurry can be collected from the suction hole  40   t  of the inner cylinder  40   b  of the double pipe rod  40 . Furthermore, since the mineral lifting pump  25  is connected to an upper end of the inner cylinder  40   b  of the double pipe rod  40  via the suction pipe  5 , the seabed minerals crushed by drilling can be suctioned through the water suction hole  50   k  of the bit  50  and lifted up to the mining mother ship  1  on the sea level. 
     Next, a description will be given of steps of lifting minerals from a seabed ore deposit OD by the above-described mining system, and operations and effects of the seabed mineral mining system and a seabed mineral mining method by the mining device  30 . 
     First, as illustrated in  FIG. 1 , the mining mother ship  1  and the erection and installation mother ship  2  are anchored on the sea level SL in a target sea region. Next, the mining stations  20  and the mineral lifting unit  4  are lifted down into the sea by using the work machine  11  such as a crane installed on the erection and installation mother ship  2 , and installed at appropriate positions on the seabed SB such that these pieces of equipment are arranged as illustrated in  FIG. 1 . Before or after installation of these pieces of equipment, necessary piping and wiring for the suction pipe  5 , the mineral lifting pipe  6 , the discharge pipe  7 , the umbilical cable  8 , and the like are performed, and the respective pipes are filled with sea water. 
     After the installation of the equipment, necessary electric power and control signals are supplied to the base control unit  45  and the mineral lifting unit  4  from the mining mother ship  1  via the umbilical cable  8 , whereby the mining stations  20 , the mining devices  30 , and the mineral lifting unit  4  are driven to crush seabed minerals while drilling a pit VH that is a bottomed hole in the seabed ore deposit OD. Note that, in the present embodiment, when arranging each of the mining stations  20  on the seabed ore deposit OD, the support legs  26  at the four corners of the base frame  21  are slid vertically in advance by the jack mechanism  49  in accordance with an uneven shape of the seabed SB so that the base frame  21  is in horizontal posture. 
     Herein, the high pressure water supplied from the high pressure water supply pump provided in the base frame  21  of each mining station  20  passes through the water supply passage  40   c  between the inner cylinder  40   b  and the outer cylinder  40   a  of the double pipe rod  40  of the mining device  30 , and enters the water passage hole  32  through the communication hole  33   e  from the first water inlet hole  31   b , from the water supply passage  35   c  of the connection member  35 , in  FIG. 5 . 
     The high pressure water, having entered the water passage hole  32 , is introduced to the hammer reciprocation switch mechanism. In the hammer reciprocation mechanism, the high pressure water in a hammer advanced state passes through in the order of the communication hole  33   b  of the cylinder liner  33 , the control grooves  34   a , and the communication holes  33   c ,  32 L, and  33   d , and enters the cylinder front chamber  41  at a front end of the hammer  34 . In this case, the control groove  34   c  is disconnected from the communication hole  33   a  by the outer peripheral surface of the hammer  34 . As a result, the hammer  34  retracts (moves upward in  FIG. 5 ). 
     Due to the retraction of the hammer  34 , the sea water in the cylinder rear chamber  42  on a rear side of the hammer  34  passes through the drainage passage  38   a , and is discharged toward the suction hole  38   t  from the discharge hole  38   g  through the check valve  37 . 
     Next, as illustrated in  FIG. 6 , when the hammer  34  reaches a retraction limit, the communication hole  33   b  formed in the cylinder liner  33  is disconnected by the outer peripheral surface of the hammer  34 . On the other hand, the communication hole  33   a  communicates with the control groove  34   c  formed on the outer peripheral surface of the hammer  34 . Thus, the high pressure water from the water passage hole  32  of the cylinder  31  flows into the cylinder rear chamber  42  on the rear side of the hammer  34 . 
     Due to the inflow of the high pressure water into the cylinder rear chamber  42 , the hammer  34  shifts from retraction to advancement, and strikes a rear end face of the bit  50  at a predetermined striking position. In the struck bit  50 , chips  50   b  at a leading end thereof apply a striking force to a drilling surface to crush the seabed minerals. 
     The high pressure water continues to be supplied to the mining device  30  from the high pressure water supply pump, whereby the hammer  34  repeatedly strikes the read end face of the bit  50  by the above-described reciprocating movement. Then, in addition to the striking to the drilling surface at the bit  50 , feed-driving of the mining device  30  is performed by the slide movement mechanism  47  provided on the guide shell  48 , and also rotary drive of the mining device  30  is performed by a rotation mechanism of the housing unit  71 . 
     Thus, the mining device  30  can continue mining of seabed minerals while forming the pit VH by drilling on the seabed ore deposit OD. Additionally, in the mining device  30 , the mining device main body  10  of its own lies inside the pit VH, so that drilling can be continued, with an opening side of the pit VH closed. Accordingly, crushed powder of the seabed minerals are prevented or suppressed from being flown out into the sea. This prevents or suppresses sea water suspension (mining unit; mining step). 
     Then, according to the mining device  30 , at the front end of the bit  50 , the water suction hole  50   k  is open that communicates with the suction hole  38   t  of the sleeve  38 . Since the suction hole  38   t  is open along the discharge hole  38   g  inclined toward the direction of the double pipe rod  40 , flow velocity of the high pressure water passing through the suction hole  38   t  produces negative pressure in the water suction hole  50   k . As a result, the seabed minerals crushed by drilling are suctioned through the water suction hole  50   k  of the bit  50 , and the suctioned seabed minerals can be mixed with the sea water in the suction hole  38   t.    
     Herein, in the case of drilling by striking force, the crushed seabed minerals produced by the drilling are extremely small in particulate diameter and uniform in particle size. Thus, according to the mining device  30 , the crushed seabed minerals produced by drilling can be suctioned by action of the drainage flow and mixed with the sea water in the suction hole  38   t  of the mining device  30  to be able to form a slurry (slurry production unit; slurry production step). 
     Furthermore, according to the mining device  30 , the suction hole  38   t  of the sleeve  38  is directly introduced to the suction pipe  5  through the suction hole  40   t  of the inner cylinder  40   b  of the double pipe rod  40 , so that the mineral lifting unit  4  can suction the slurry of minerals mined by the mining device  30 , together with the sea water, from the suction pipe  5 . By doing this, it is possible to prevent or suppress the slurry of the seabed minerals from flying up and scattering in the sea water (collection unit; collection step). 
     Next, the mineral slurry suctioned into the suction pipe  5  is transferred to the sizer  27 . The sizer  27  separates desired one or more minerals from undesired, unnecessary minerals by centrifugal force due to specific gravity difference between mineral particles. The minerals determined not to be necessary by sizing are guided to the place for returning and leaving those unnecessary on the seabed via the discharge pipe  7  connected to the sizer  27 , as illustrated in  FIG. 1 . 
     On the other hand, among the separated minerals in the slurry, the one or more minerals having a desired specific gravity are sent to the mineral lifting pump  25 , and lifted up to the reservoir  13  of the mining mother ship  1  via the mineral lifting pipe  6 . In the mining mother ship  1 , when storing in the reservoir  13 , the one or more minerals in the slurry are separated from the sea water, as a result of which the seabed minerals are stored in the reservoir  13 , and the separated sea water is discharged in the sea. 
     When mining is done to a maximum drilling depth of each mining device  30 , each mining station  20  retracts the mining device  30 , and then moves the mining device  30  in an X-Y plane to drill holes in order in such a manner as to scan the entire X-Y plane, as illustrated in  FIG. 7B . The movement in the X-Y plane and the drilling after the movement may be automatically performed by computer (such as the above-mentioned management computer and the base control unit  45 ), as in the present embodiment, or may be performed through manual operation by an operator concurrently monitoring the state of each mining station  20  from the mining mother ship  1  on the sea level. 
     Particularly, according to the mining stations  20  each including the mining devices  30 , the seabed mineral mining system, and the mineral lifting method using these pieces of equipment, each mining station  20  includes the plurality of support legs  26 , each of which is individually relatively slidable in the Z direction via the jack mechanism  49 , which is the vertical movement mechanism, so that each mining station  20  can correspond with the slopes and undulations of seabed ore deposits. In addition, when an operator performs manual operation while monitoring through a camera or the like, scattering of seabed minerals into sea water is prevented or suppressed, which is thus suitable to improve the efficiency of mining work. 
     Herein, while a plurality of mining stations  20  can be used to simultaneously mine a wide range, as in the above embodiment, various types of mining devices  30 , from those for small diameter to those for large diameter, can also be used as the mining devices  30  equipped in each mining station  20 . 
     For example, as illustrated in  FIG. 7A , after mining using the mining station  20  equipped with mining devices  30  for small diameter, the same region can be further mined using an other mining station  20  equipped with mining devices  30  for large diameter or using the same mining station  20  equipped with replaced mining devices  30  for large diameter, as illustrated in  FIGS. 8A and 8B . Note that reference signs  50  and  50 B in  FIGS. 7A, 8A and 8B  do not mean replacement by bits only but overall replacement by mining devices  30  corresponding to a small-diameter bit  50  or a large-diameter bit  50 B. 
     Thus, according to the mining stations  20  each including the mining devices  30 , the seabed mineral mining system, and the mineral lifting method using these pieces of equipment, it is possible to correspond with the slopes and undulations of seabed ore deposits, and furthermore, the slurry of seabed minerals is in the pits VH, which prevents or suppresses flying up and scattering of the seabed minerals in the sea water. Additionally, the mining system of the present embodiment directly introduces the slurry of seabed minerals mined by the mining devices  30  to the suction pipe  5  from insides of the pits VH, which thus can also prevent or suppress scattering in the sea water at the time of mineral lifting. 
     It should be noted that the present invention is not limited to the above embodiment, and it is obvious that various modifications can be made without departing from the spirit of the present invention. 
     For example, while the above embodiment has described the example of the mining mother ship  1  as the offshore mining base, the present invention is not limited thereto. The offshore mining base may be, for example, a platform erected on the sea, or the like, as long as it serves as an offshore mineral lifting base. 
     Additionally, for example, while the above embodiment has described the example where the mineral slurry is transported to the reservoir  13  provided in the mining mother ship  1 , the present invention is not limited thereto. Minerals mined in the seabed and directly transported from the inside of the pit VH that is a bottomed hole may be lifted, stored, or sized in the vicinity of the mining mother ship  1  on the sea level or under the sea level (e.g. there is provided a reservoir near the ship bottom thereof). 
     In addition, for example, while the above embodiment has described the example where the pit VH is drilled as one example of a bottomed hole, the bottomed hole according to the present invention is not limited to a hole having a vertical axial line. In other words, in the present invention, it is sufficient that a bottomed hole can be formed by drilling, then seabed minerals can be formed into a slurry in the bottomed hole, and the slurry can be collected from the inside of the bottomed hole. Therefore, the bottomed hole according the present invention may be a lateral hole having a horizontal axis line or may be a hole having an oblique axis line. 
     In addition, the method and device for forming the pit VH are not limited to drilling with a striking mechanism, and may be drill boring with a rotation mechanism. However, to form mined minerals into a slurry and make particle diameters very small to uniformize particle sizes, drilling with a striking mechanism is preferable to drill boring. 
     Additionally, for example, while the above embodiment has described the example where the mineral lifting unit  4  includes the sizer  27 , and the slurry of minerals are sized by the sizer  27  in the sea, the present invention is not limited thereto. With the mining device according to the present invention, mined minerals are in the form of slurry, whose particle diameter is extremely small, and whose particle size is uniform, so that the seabed minerals in the form of slurry may be lifted up without sizing. 
     Furthermore, for example, while the above embodiment has described the example where the mining device  30  includes the double pipe rod  40  including the outer cylinder  40   a  and the inner cylinder  40   b , the present invention is not limited thereto. For example, as illustrated in  FIG. 9 , a mining device may be formed using a single pipe rod. 
     In other words, as illustrated in the drawing, a mining device  130  includes a single pipe rod  57 , and a mining device main body  100  is installed ahead of the rod  57 . The mining device main body  100  includes a cylinder  56  connected to a leading end of the rod  57  by a tapered screw portion  56   a . In the cylinder  56 , a check valve  51 , a hammer  54 , and a bit  50  are provided in order from the top, and a cylinder front chamber  52  and a cylinder rear chamber  53  are defined in front of and behind the hammer  54 . 
     High pressure water for driving the mining device  130  is supplied to the housing unit  71  at an upper end of the rod  57  via the high pressure water supply pipe  9  from the high pressure water supply pump, as in the above embodiment. The supplied high pressure water is supplied to and discharged from the cylinder front chamber  52  or the cylinder rear chamber  53  so as to move the hammer  54  forward and backward in the cylinder  56  by the hammer reciprocation switch mechanism formed on inner and outer peripheral surfaces of the cylinder  56  and the hammer  54 , as in the above embodiment. In addition, the rod  57  is rotated and fed by the slide movement mechanism  47  provided on the guide shell  48  and the rotation mechanism of the housing unit  71 . 
     Herein, in the mining device  130 , the cylinder  56  is provided with a foot pad  58  capable of being pressed toward a drilled hole opening side and being slidable along the axial direction so as to surround a periphery of the drilled hole. To an upper side face of the foot pad  58  is connected to the suction pipe  5  to mine the slurry as a seabed mineral resource. 
     In the mining device  130  thus formed, the high pressure water passes through the check valve  51  at an upper part, and is supplied to or discharged from the cylinder front chamber  52  and the cylinder rear chamber  53  by the hammer reciprocation switch mechanism to drive the hammer  54  forward and backward, whereby an impact due to striking of the hammer  54  against the bit  50  drills the pit VH that is a bottomed hole in the seabed ore deposit OD (mining unit; mining step). 
     While the high pressure water after the striking flows out to a leading end of the bit through the suction hole  50   a  provided at an axial center of the bit  50 , seabed minerals mined by the drilling is mixed with sea water in the pit VH to be formed into a slurry (slurry production unit; slurry production step). 
     Then, the slurry produced in the pit VH passes through a gap between an outside of the cylinder  56  and a drilled hole inner wall VHn or a gap between an outside of the rod  57  contacted with the drilled hole inner wall VHn and extending into the sea water and the drilled hole inner wall VHn, and is directly collected from the inside of the pit VH via the suction pipe  5  from an inside of the foot pad  58  (collection unit; collection step). Thus, even with the structure as in the mining device  130 , scattering of the mined minerals in the sea can be prevented or suppressed. 
     Additionally, for example, while the above embodiment has described the example whereas the undersea mining base, each mining station  20  itself does not move horizontally, the present invention is not limited thereto. For example, as illustrated in  FIGS. 10A to 10C , each mining station can be configured to include a mechanism allowing itself to move horizontally. 
     Herein, regarding an excavator for mining mineral resources in seabed ore deposits, a main concept that has been proposed so far is a method in which, using a crawler-type remote controlled excavator, a seabed ore deposit is mined horizontally by a drum cutter mounted in the excavator while travelling by crawler. This will be hereinafter referred to as horizontal mining system (HMS). The HMS is excellent in mobility and portability, and can mine while traveling freely on a seabed. On the other hand, the HMS has problems to be solved in terms of the following points (Problem 1) to (Problem 5): 
     (Problem 1): Large friction force is required to ensure mining reaction force of the drum cutter within a mining plane. Due to that, it is necessary to increase the weight of an excavator main body. 
     (Problem 2): Minerals crushed at drilling fly up in the water, and lower visibility. In operation of the HMS, an operator on the sea needs to visually operate through a camera, which thus may affect operation rate. Additionally, load on environment may also be significant. 
     (Problem 3): Operation corresponding with the undulations of the seabed is necessary, and excavation is performed while visually observing through a camera, thus making full automation difficult. 
     (Problem 4): Climbing ability corresponding with the inclined angle of a mine is necessary. In addition, even if not on an inclined land, when the ground of the seabed is soft, it may be difficult to travel by crawler. 
     (Problem 5): Depending on a contrivance of the shape of the drum cutter, a subsea crushing unit (SCU) is said to be necessary due to non-uniform sizes of mined ores. 
     Thus, in the HMS, which is a crawler-type excavator, operation corresponding with the undulations of the seabed is complicated, and automation is difficult. Additionally, seabed ore deposits have large inclined angles, thus making it difficult to travel by crawler on soft ground accumulated on the surface thereof. Particularly, on seabed hydrothermal deposits, there are many chimneys spouting hot water (chimney-like hot water spouting protrusions) on seamounts, and it is difficult to avoid such chimneys. Thus, to solve such problems of the HMS, the present inventors have invented the above first embodiment, which is a vertical mining system (VMS), as a method different from the HMS. 
     Merits of the VMS are summarized at least as in the following (Effect 1) to (Effect 4): 
     (Effect 1): Ores are crushed into an extremely fine powder, so that the subsea crushing unit (SCU) can be omitted. 
     (Effect 2): Since a seabed ore deposit is longitudinally mined, ores crushed by mining are sucked out using a flow line, similarly to riser excavation, so that scattering to environment is small. Thus, the load on the environment is also small, and low visibility can be prevented when an operator monitors through a camera from above the sea. 
     (Effect 3): It is possible to mine a section at a bottom-landing position (a predetermined range), so that according to a predetermined program, mining can be automatically performed without any problem of visibility. 
     (Effect 4): Each mining station is erected on the seabed, and each support leg thereof is individually relatively slidable in the Z direction via the vertically movement mechanism. Thus, the system is applicable to complicated seabed shapes and soft ground to which it will be difficult to apply the HMS. 
     However, as for the mining station  20  of the first embodiment, after completing the mining of a first section, it is necessary to install the mining station  20  again in a next adjacent section. In other words, the mining station  20  of the first embodiment requires an installation and relocation vessel (IRV) every time a jack-up type platform is installed and relocated. 
     Due to that, much time and cost are needed for work for lifting, relocation, and bottom landing of the VMS by the IRV. In addition, since the IRV is always used during the mining period, cost for use is large. By contrast, second and third embodiments, which will be described below, solve the problems, and are each a VMS movable by itself in at least one direction of the X and Y directions, e.g., a self-traveling vertical mining system for developing seabed mineral resources. 
     Specifically, a mining station  120  of the second embodiment is formed using three base frames including a first base frame  21 A, a second base frame  21 B, and a third base frame  21 M, as illustrated in  FIG. 10A . 
     The first base frame  21 A and the second base frame  21 B are each formed of a U-shaped frame body. The first and second frames  21 A and  21 B are each provided with the support legs  26  each provided at two corner portions forming a U-shape via the jack mechanism  49 , as in the above embodiment. The U-shape of the first base frame  21 A has a width narrower than the width of the U-shape of the second base frame  21 B. 
     The first base frame  21 A and the second base frame  21 B are arranged to face each other such that opening portions of the U-shapes of the mutual frames  21 A and  21 B can be combined together. Horizontal frames of the mutual frames  21 A and  21 B are engaged with each other on facing surfaces thereof via an unillustrated first rack and pinion mechanism and a first sliding guide device such as a linear guide, and are relatively slidable in the X direction by driving the first rack and pinion mechanism by an unillustrated first motor. 
     The third base frame  21 M is formed into an I-shape from a vertical frame extending in the Y direction. In the third base frame  21 M, the support legs  26  are each provided at both ends of the I-shape via the jack mechanism  49 , as in the above embodiment. Additionally, the third base frame  21 M includes a Y-direction movement mechanism and the guide shell  48 , and can slide the guide shell  48  in the Y direction along the movement frame  43 . Note that the guide shell  48  is equipped with a mining device similar to that of the above embodiment. 
     The third base frame  21 M is arranged in a direction orthogonal to the horizontal frames with respect to the first base frame  21 A and the second base frame  21 B. The third base frame  21 M is engaged with respect to the horizontal frames of the first and second frames  21 A and  21 B on facing surfaces thereof via an unillustrated second rack and pinion mechanism and a second sliding guide device such as a linear guide, and is relatively slidable in the X direction by driving the second rack and pinion mechanism by an unillustrated second motor. 
     When the mining station  120  moves, as illustrated in  FIG. 10B , first, the jack mechanism  49  of the first base frame  21 A is driven to move the two support legs  26  of the first base frame  21 A upward so as to be in a non-supporting state. Next, the first rack and pinion mechanism is driven by the first motor to relatively slide the first base frame  21 A in a positive direction of the X direction with respect to the second base frame  21 B. After the sliding, the first motor is stopped, and the jack mechanism  49  is driven to move the two support legs  26  of the first base frame  21 A downward so as to be in a supporting state. 
     Next, as illustrated in  FIG. 10C , first, the jack mechanism  49  of the second base frame  21 B is driven to move the two support legs  26  of the second base frame  21 B upward so as to be in the non-supporting state. Then, the first rack and pinion mechanism is driven by the first motor to relatively slide the second base frame  21 B in the positive direction of the X direction with respect to the first base frame  21 A. After the sliding, the first motor is stopped, and the jack mechanism  49  is driven to move the two support legs  26  of the second base frame  21 B downward so as to be in the supporting state. 
     Next, the jack mechanism  49  of the third base frame  21 M is driven to move the two support legs  26  of the third base frame  21 M upward so as to be in the non-supporting state. Then, the second rack and pinion mechanism is driven by the second motor to relatively slide the third base frame  21 M in the positive direction of the X direction with respect to the first and second base frames  21 A and  21 B. After the sliding, the second motor is stopped, and the jack mechanism  49  is driven to move the two support legs  26  of the third base frame  21 M downward so as to be in the supporting state. As a result, the entire three base frames  21 A,  21 B, and  21 M are brought into a state illustrated in  FIG. 10A  while moving in the positive direction of the X direction by an amount corresponding to an amount of the sliding. 
     Thus, according to the mining station  120 , sequentially moving the three base frames  21 A,  21 B, and  21 M in the manner described above allows the entire mining station  120  to move by itself in the X direction. Note that when sliding, the base frames  21 A and  21 B overhang in a cantilevered state, but are mutually engaged on the facing surfaces via the sliding guide device, so that horizontal posture is maintained. 
     In addition, the third base frame  21 M includes the Y-direction movement mechanism, as in the above first embodiment, whereby the guide shell  48  can be slid in the Y direction along the movement frame  43 . The guide shell  48  is equipped with the mining device  30  similar to the above embodiment. Thus, the mining device  30  can be driven while moving the guide shell  48  in the Y direction, as appropriate, at a time when the third base frame  21 M is not moved. 
     Accordingly, even with such a structure, each mining device  30  is movable in the X direction and the Y direction, whereby seabed minerals can be mined while forming a pit that is a bottomed hole by drilling while corresponding with the slopes and undulations of a seabed ore deposit, and formed into a slurry in the pits, and then the slurry can be directly collected from the insides of the pits. 
     Next, the third embodiment of the present invention will be described with reference to  FIGS. 11 to 30 , as appropriate. The third embodiment is a self-traveling vertical mining system for developing seabed mineral resources, capable of moving a mining station in the X direction and the Y direction, and, particularly, is an example of an undersea mining base that is a self-traveling seabed excavation machine including a vertical hole excavation drill. 
       FIG. 11  illustrates a schematic perspective diagram of an entire mining station of the third embodiment. As illustrated in the drawing, a mining station  220  includes the mining device  30  and a platform  21  capable of self-traveling in the X direction and the Y direction. The platform  21  includes an upper platform  21 X having a rectangular frame shape in a plan view, a lower platform  21 Y having a rectangular frame shape in a plan view, and a middle frame  21 M provided between both platforms  21 X and  21 Y and having a rectangular frame shape in a plan view. 
     Note that the mining station  220  of the third embodiment has the same structure as that of the above first embodiment, except for the platform  21  and a movement mechanism for moving in the X direction and the Y direction included in the platform  21 . Thus, the third embodiment will describe the platform  21  and the movement mechanism for moving in the X direction and the Y direction, and descriptions of other mechanisms will be omitted as appropriate. 
     Hereinafter, a detailed description of the movement mechanism of the mining station  220  of the third embodiment will be given with reference to  FIGS. 12 to 19 . Note that  FIGS. 12 and 13  illustrate a bottom-landing posture of the platform  21  when the mining station  220  is landed on the seabed ore deposit OD from the erection and installation mother ship  2 . When the platform  21  is in the bottom-landing posture, centers (the centers of gravity) G in a horizontal plane of the upper platform  21 X, the middle frame  21 M, and the lower platform  21 Y are coincident. Note that, in  FIG. 13 , reference sign CL denotes a center axis line of each support leg  26 . 
     As illustrated in  FIG. 12 , the upper platform  21 X has a rectangular frame shape in a plan view, and includes a pair of rectangular cylindrical longitudinal girders Xb spaced apart from each other in the X direction and arranged parallel to each other and a pair of rectangular cylindrical lateral girders Xa spaced apart from each other in the Y direction and arranged parallel to each other. On each outer side face of the two lateral girders Xa, an X moving rack Rx is each attached symmetrically from a center in an extending direction of each lateral girder Xa. 
     Additionally, as illustrated in the drawing, the lower platform  21 Y has a rectangular frame shape in a plan view, and includes a pair of rectangular cylindrical lateral girders Yb spaced apart from each other in the X direction and arranged parallel to each other and a pair of rectangular cylindrical longitudinal girders Ya spaced apart from each other in the Y direction and arranged parallel to each other. On each outer side face of the two longitudinal girders Ya, a Y moving rack Ry is each attached symmetrically from a center in an extending direction of each longitudinal girder Ya. 
     As illustrated in  FIG. 14 , the middle frame  21 M has a rectangular shape in a plan view, and includes a pair of rectangular cylindrical longitudinal girders Mb spaced apart from each other in the X direction and arranged parallel to each other and a pair of rectangular cylindrical lateral girders Ma spaced apart from each other in the Y direction and arranged parallel to each other. At a center position in an extending direction of each lateral girder Ma of the middle frame  21 M, an X drive motor Mx is each arranged in the rectangular cylinder of the lateral girder Ma. Additionally, at a center position in an extending direction of each longitudinal girder Mb of the middle frame  21 M, a Y drive motor My is each arranged in the rectangular cylinder of the longitudinal girder Mb. 
     As illustrated in  FIGS. 11 and 12 , the respective upper and lower platforms  21 X and  21 Y are jack-up platforms each including the four support legs  26  and the jack mechanisms  49  capable of ascending and descending each support leg  26 , similarly to the platform of the above first embodiment. Then, the middle frame  21 M and the upper and lower platforms  21 X and  21 Y are supported so as to be slidable via a linear motion guide mechanism illustrated in  FIGS. 16 and 17 , and also are engaged via a rack and pinion mechanism illustrated in  FIGS. 17 and 18 , thereby being configured so as to be relatively slidable in the X direction and the Y direction orthogonal to each other on the horizontal plane. 
     Specifically, as illustrated in  FIG. 12 , the platform  21  of the third embodiment includes the support leg  26  at each of four corners of a rectangular frame body of the upper platform  21 X and at each of four corners of a rectangular frame body of the lower platform  21 Y. Each support leg  26  includes the jack mechanism  49  that is a slide movement mechanism in the Z direction, as a jacking unit for ascending and descending. 
     Each support leg  26  is equipped with a total of two jack mechanisms  49  of the third embodiment, each one at both sides thereof. In each support leg  26 , two Z movement racks Rz are arranged at positions facing each other in a circumferential direction along the axial direction of each support leg  26 , as illustrated in  FIG. 15 . 
     The jack mechanism  49  corresponding to each Z movement rack Rz includes an unillustrated Z drive motor, a pinion attached to an output shaft of the Z drive motor, and the above Z movement rack Rz meshed with the pinion to form the rack and pinion mechanism. As a result, each support leg  26  can relatively slide in the Z direction with respect to the respective platforms  21 X and  21 Y equipped with itself, thereby enabling ascending and descending of the upper and lower platforms  21 X and  21 Y by cooperation of the plurality of support legs  26 . 
     The linear motion guide mechanism of the upper platform  21 X includes a skidding rail Sx attached onto lower surfaces of the lateral girders Xa of the upper platform  21 X along the extending directions of the lateral girders Xa, as illustrated in  FIG. 16 . The skidding rail Sx is attached from one end to the other end of the lateral girder Xa of the upper platform  21 X along the lateral girder Xa of the upper platform  21 X. 
     Upper and lower portions of the skidding rail Sx are guided by a bearing plate Bx measuring, for example, about 200 mm×200 mm. The bearing plate Bx is attached onto a corner upper surface of the lateral girder Ma of the middle frame  21 M. Additionally, a holding claw Hx is attached at the same position as the arrangement position of the bearing plate Bx in such a manner as to cover the skidding rail Sx from right and left sides thereof. The holding claw Hx supports the skidding rail Sx from both sides thereof so as to prevent the upper platform  21 X from falling when moving in the X direction. 
     As illustrated in  FIG. 18 , each X movement pinion Px is attached to a drive shaft of each X drive motor Mx, and protrudes at a position facing a rack surface of each X movement rack Rx. The two X movement pinions Px are configured to be respectively meshed with the X movement racks Rx and synchronously driven by the X drive motors Mx so that the upper platform  21 X are slidable in the X direction. 
     On the other hand, the linear motion guide mechanism of the lower platform  21 Y includes a skidding rail Sy attached onto upper surfaces of the longitudinal girders Ya of the lower platform  21 Y along the extending directions of the longitudinal girders Ya, as illustrated in  FIG. 17 . The skidding rail Sy is attached from one end to the other end of the longitudinal girders Ya of the lower platform  21 Y. 
     Similarly to the upper platform  21 X, in the lower platform  21 Y a bearing plate By is attached onto a corner lower surface of the longitudinal girder Mb of the middle frame  21 M, and the bearing plate By guides upper and lower portions of the skidding rail Sy. Additionally, a holding claw Hy is attached at the same position as the arrangement position of the bearing plate By in such a manner as to cover the skidding rail Sy from right and left sides thereof, and supports the skidding rail Sy from both sides thereof so as to prevent the lower platform  21 Y from falling when moving in the Y direction. 
     As illustrated in  FIG. 19 , Y movement pinions Py are attached to a drive shaft of the Y drive motor My, and protrude at a position facing a rack surface of each Y movement rack Ry. The two Y movement pinions Py are configured to be respectively meshed with the Y movement racks Ry, and synchronously driven by the Y drive motors My so that the lower platform  21 Y are slidable in the Y direction. 
     Thus, the mining station  220  of the third embodiment is configured to be capable of walking in each of the X direction and the Y direction in a predetermined mining region, and moving the mining devices  30  in the X direction and the Y direction to sequentially drill predetermined sections according to steps for walking control processing, which will be described later, by the slide movement mechanism configured to slide the upper and lower platforms  21 X and  21 Y in the X direction and the Y direction and the slide movement mechanism configured to slide each support leg  26  in the Z direction. 
     Note that, in the third embodiment, the middle frame  21 M and the upper and lower platforms  21 X and  21 Y represent examples in which horizontal movement can be performed via the rack and pinion mechanism, but the movement mechanism is not limited thereto. Any of various movement mechanisms can be employed as long as it is a movement mechanism enabling horizontal movement. 
     For example, a movement mechanism configured to slide by a hydraulic cylinder method can be used. Similarly, each support leg  26  represents an example in which relative sliding in the Z direction can be performed via the rack and pinion mechanism, but a movement mechanism is not limited thereto. For example, it is possible to use a movement mechanism configured to slide by a hydraulic cylinder method. Additionally, the movement mechanism is not limited to a hydraulically driven type, and may be an electrically driven type. 
     Herein, the third embodiment assumed, as the specifications of the mining station  220 , a total production capacity (Dry SMS) of 2,000,000 t/year (6,600 t/day), a density of from 3 to 5 (t/m 3 ), and a volume of 6600/5 to 6600/3=1320 to 2200 m 3 , and determined the size of a predetermined region (section) to be drilled by one mining station  220  to be about 10 m×10 m. Additionally, the mining device  30  is assumed to have a structure capable of drilling to a depth of about 20 m. 
     Then, given the above production capacity, the third embodiment assumes that one mining station  220  drills one section, which is a predetermined region having a depth of 20 m, per day. Additionally, in the third embodiment, when the mining station  220  is a self-traveling type, the platform  21  can move to an adjacent section in a short time. Thus, it is also considered to drill two sections, which are two predetermined regions each 10 m in depth, per day. 
     Specifically, when the width occupied by the movement mechanism  52  and the mining device  30  illustrated in the above first embodiment is assumed to be 3 m, setting the size of a drilling section as a predetermined region to 10 m×10 m requires setting the size of an inner drilling region in the platform  21  to 13 m×10 m. Furthermore, dimensions of the shapes of the upper platform  21 X, the lower platform  21 Y, and the middle frame  21 M were set in consideration of loading conditions in towing, hanging, and working. 
     As for the shape and dimensions of each support leg  26  described above, when a total axial length of the support leg  26  was 30 m, an outer diameter D thereof was set to 1000 mm from loading conditions in rolling, mainly in consideration of towing conditions, as illustrated in the cross-section of the support leg  26  of  FIG. 15 . 
     In addition, in  FIG. 12 , from the loading conditions in towing, hanging, and working, a length Lx in the X direction and a width Ly in the Y direction inside the girders of the upper platform  21 X were set to 23 m and 10 m, respectively. Additionally, a width Wg and a thickness Dg of the girders themselves of the upper platform  21 X were set to 1 m and 2 m, respectively. 
     In addition, in the drawing, the length Lx in the X direction and the width Ly in the Y direction inside the girders of the lower platform  21 Y were set to 13 m and 20 m, respectively. Additionally, the width Wg and the thickness Dg of the girders themselves of the lower platform  21 Y were set to 1 m and 2 m, respectively. Furthermore, as for the middle frame  21 M, the length Lx in the X direction and the width Ly in the Y direction inside the girders of the middle frame  21 M were set to 13 m and 10 m, respectively, as illustrated in  FIG. 14 . 
     In addition, the width Wg and the thickness Dg of the girders themselves of the middle frame  21 M were both set to 1 m. Additionally, in the rack and pinion mechanism portion illustrated in  FIG. 16 , the rack had a length of about 10 m. Furthermore, in the rack and pinion mechanism portion illustrated in  FIG. 17 , the rack had a length of about 10 m. 
     In the plan view illustrated in  FIG. 12 , a rectangular portion inside the frame body at a center in a state where the upper platform  21 X, the lower platform  21 Y, and the middle frame  21 M overlap has dimensions of 13 m×10 m. Since the width of the movement mechanism  52  and the mining device  30  is 3 m, the size of a predetermined section that can be excavated is 10 m×10 m.  FIG. 20  illustrates an image of a relative size of the mining station  220  on the seabed ore deposit OD in the case of the dimensions set as above, in which the mining station  220  arranged undersea and erected on a seabed is forming the pit VH. Note that reference sign C in the drawing denotes an image of a chimney present on the seabed ore deposit OD. 
     Furthermore, as illustrated in  FIG. 11 , the mining station  220  of the third embodiment includes a base control unit  45  for controlling the mining station  220  itself on the upper platform  21 X. The base control unit  45  of the third embodiment includes a tilt sensor configured to detect posture of the platform  21 . 
     Still furthermore, in the third embodiment, each jack mechanism  49  driving each support leg  26  is equipped with an unillustrated torque detector. Each torque detector is a torque meter capable of detecting torque of each drive motor configured to drive the pinion of the rack and pinion mechanism of each corresponding jack mechanism  49 . Each torque detector can detect motor torque of each drive motor as needed, and can output detected torque information to the base control unit  45 . 
     The base control unit  45  is a controller (a control unit) of the mining station itself including a computer and a program for executing posture stabilization control processing. The base control unit  45  executes walking control processing for the mining station  220 , mining control processing for the mining station  220 , posture control for the mining station  220 , and other necessary processing. 
     When the posture control processing for the mining station  220  is executed, the base control unit  45  determines the degree of imbalance in the posture of the mining station  220  itself on the basis of output of the tilt sensor, and performs posture stabilization control for maintaining posture stability by adjustment of each drive motor configured to drive the pinion of the rack and pinion mechanism. 
     Additionally, the base control unit  45  outputs inclination information detected by the tilt sensor and motor torque information regarding detected motor torques of the plurality of support legs  26  to the management computer equipped in the erection and installation mother ship  2 , which is a towing vessel on the sea. The management computer is configured to be capable of displaying the inclination information and the motor torque information on a display, for the operator, as needed. 
     Next, a description will be given of a stabilized sitting method for the mining station  220  of the third embodiment, with reference to  FIGS. 21A, 21B and 22A to 22D  as appropriate. 
     When landing the mining station  220  on the seabed by hanging with hanging rope from the erection and installation mother ship  2 , which is the towing vessel on the sea, the mining station  220  is first placed in a state of bottom-landing preparation posture illustrated in  FIG. 12  in a plan view. As illustrated in  FIG. 21A , the operator hangs down the mining station  220  with rope from the erection and installation mother ship  2 . 
     As illustrated in  FIG. 22A , while paying attention to a dropped depth, the operator lowers the mining station  220  to an intended position on the seabed ore deposit OD. Then, the operator stops the hanging upon detection of responses of motor torques of at least three legs among the plurality of support legs  26 , as illustrated in  FIG. 22B . However, if after sitting of one leg of the support legs  26 , the inclination angle exceeds a predetermined one before sitting of the other three legs, the sitting position is changed. Note that the hanging operation may be performed by manual operation of the base control unit  45  by the operator via the management computer or may be automatically controlled by the management computer and the base control unit  45 . For example, the base control unit  45  of the mining station  220  executes the posture stabilization control upon acquisition of hanging operation termination information (sitting information). 
     In other words, on the basis of the posture detection information of the tilt sensor, the base control unit  45  extends or retracts the landed support legs  26  so that the posture of the mining station  220  becomes horizontal, as illustrated in  FIG. 22C . Based on the motor torque information, the base control unit  45  extends the support leg(s)  26  not landed, and controls so that the motor toques of the respective support legs  26  are substantially balanced, whereby the support leg(s)  26  is/are landed. The base control unit  45  transmits termination information on the posture stabilization control to the management computer of the erection and installation mother ship  2  when it determines the posture of the mining station  220  is horizontal. 
     The operator in the erection and installation mother ship  2  monitors the state of the mining station  220  through the display of the management computer, and, upon confirmation of the termination information on the posture stabilization control, inputs a command for loosening tension of the hanging rope through the management computer, as illustrated in  FIG. 22D . In this case, due to tension fluctuation of the hanging rope, the posture of the mining station  220  may be unstabilized. Thus, the base control unit  45  continuously executes the posture stabilization control. 
     Specifically, on the basis of the posture detection information of the tilt sensor, the base control unit  45  adjusts a leg length of each support leg  26  so that the posture of the mining station  220  becomes horizontal. By doing this, the mining station  220  can be landed in a stabilized posture in an initial landed state illustrated in  FIG. 22D  on the seabed. After this, the operator cancels engagement of the hanging rope by an engagement cancellation device (unillustrated) for the hanging rope, and allows the self-standing mining station  220  to form the pit VH on the seabed ore deposit OD to start mining, as illustrated in  FIG. 21B . Note that the structures and stabilized sitting method of the management computer and the base control unit  45  including the stabilized sitting control can also be applied to the first and second embodiments described above. 
     Next, a self-travelling method for the mining station  220  of the third embodiment will be described with reference to  FIGS. 23 to 33  as appropriate. Herein, as one example, a description will be given of steps for mining a seabed ore deposit OD measuring 40×40 m by self-travelling and excavation of the mining station  220 , as illustrated in  FIG. 23 . Note that self-traveling operation of the mining station  220 , which will be described below, is performed on the basis of a predetermined program executed by the base control unit  45  under monitoring of the management computer, but not limited thereto, and may be performed by manual operation by the operator. 
     (Step 1) Preparation Step 
     When the mining station  220  is in the initial landed state illustrated in  FIG. 22D , relative positions of the upper and lower platforms  21 X and  21 Y are those in the bottom-landing preparation posture illustrated in  FIGS. 11 and 12 , in which all the support legs  26  of the upper and lower platforms  21 X and  21 Y are landed. 
     Thus, upon receipt of a mining preparation command from the management computer, the base control unit  45 , first, once releases all the support legs  26  of the upper platform  21 X from the seabed, from the bottom-landing preparation posture of (a) of  FIG. 24 , and moves the upper platform  21 X fully in the positive direction of X in a state where the middle frame  21 M and the lower platform  21 Y are joined together, as illustrated in a plan view of  FIG. 24 . After that, the base control unit  45  allows all the support legs  26  of the upper platform  21 X to be landed to start mining, as illustrated in (b) of  FIG. 24 . As a result, the predetermined region inside the upper and lower platforms  21 X and  21 Y becomes a first section A illustrated in  FIG. 23 . 
     (Step 2) Walking and Excavation in Positive Direction of X 
     (Step 2-1) In the first section A, the base control unit  45  of the mining station  220  receives a mining start command from the management computer, and then mines a predetermined region (10 m×10 m) inside the middle frame  21 M. When mining one section, the base control unit  45  stops walking of the mining station  220 , and, in this state, performs mining while excavating the 10×10 m predetermined region inside the middle frame  21 M sequentially by movement of the mining device  30  in the X direction and the Y direction in the method illustrated in  FIGS. 7A and 7B  (hereinafter the same). 
     (Step 2-2) After completion of the intended mining in the first section A, the base control unit  45  moves the platform  21 , as illustrated in  FIG. 30 , by driving and controlling respective portions, as illustrated in  FIGS. 25A to 25D , so that the predetermined region inside the middle frame  21 M comes to a position corresponding to a second section B illustrated in  FIG. 23 . 
     In other words, in the state where the mining of the first section A is completed, all the support legs  26  of the upper and lower platforms  21 X and  21 Y are landed, as illustrated in  FIG. 26 . 
     Thus, the base control unit  45  first releases the four support legs  26  of the lower platform  21 Y from the seabed, while keeping the support legs  26  of the upper platform  21 X landed, as illustrated in  FIG. 27 . 
     Next, as illustrated in  FIG. 28  and (b) of  FIG. 30 , the base control unit  45  moves the lower platform  21 Y and the middle frame  21 M fully in the positive direction of X in a state where the lower platform  21 Y and the middle frame  21 M are joined together. After that, as illustrated in  FIG. 29 , the base control unit  45  extends the four support legs  26  of the lower platform  21 Y downward to allow each to land. As a result, as illustrated in (c) of  FIG. 30 , the predetermined region inside the upper and lower platforms  21 X and  21 Y becomes the second section B illustrated in  FIG. 23 . 
     (Step 2-3) In the second section B, the base control unit  45  of the mining station  220  receives a mining start command from the management computer, and then mines the predetermined region inside the middle frame  21 M. 
     (Step 2-4) After completion of the intended mining in the second section B ((c) of  FIG. 30 ), the base control unit  45  releases the four support legs  26  of the upper platform  21 X from the seabed while keeping the support legs  26  of the lower platform  21 Y landed. Then, the base control unit  45  moves the upper platform  21 X fully in the positive direction of X, as illustrated in (a) of  FIG. 31 , in the state where the lower platform  21 Y and the middle frame  21 M are joined together. After that, the four support legs  26  of the upper platform  21 X are landed. 
     Next, while keeping the support legs  26  of the upper platform  21 X landed, the base control unit  45  releases the four support legs  26  of the lower platform  21 Y from the seabed, and moves the lower platform  21 Y and the middle frame  21 M fully in the positive direction of X, as illustrated in (b) of  FIG. 31 , in the state where the lower platform  21 Y and the middle frame  21 M are joined together. After that, the four support legs  26  of the lower platform  21 Y are extended downward to be each landed. As a result, as illustrated in (c) of  FIG. 31 , the predetermined region inside the upper and lower platforms  21 X and  21 Y becomes a third section C illustrated in  FIG. 23 . 
     (Step 2-5) Hereinbelow, similarly, after completion of the predetermined mining in the third section C, the base control unit  45  releases the support legs  26  of the upper platform  21 X from the seabed while keeping the support legs  26  of the lower platform  21 Y landed. Then, the base control unit  45  moves the upper platform  21 X and the middle frame  21 M fully in the position direction of X, as illustrated in (d) of  FIG. 31 , in the state where the upper platform  21 X and the middle frame  21 M are joined together. 
     Next, while keeping the support legs  26  of the upper platform  21 X landed, the base control unit  45  releases the support legs  26  of the lower platform  21 Y from the seabed. Then, the base control unit  45  moves the lower platform  21 Y and the middle frame  21 M fully in the positive direction of X, as illustrated in (e) of  FIG. 31 , in the state where the lower platform  21 Y and the middle frame  21 M are joined together. After that, the support legs  26  of the lower platform  21 Y are landed. As a result, as illustrated in (f) of  FIG. 31 , the predetermined region inside the upper and lower platforms  21 X and  21 Y becomes a fourth section D illustrated in  FIG. 23 . 
     (Step 2-6) In the fourth section D, the base control unit  45  receives a mining start command from the management computer, and then mines the predetermined region inside the middle frame  21 M. 
     (Step 2-7) Hereinbelow, similarly, the steps (2-4) to (2-6) are repeated for the walking and excavation in the positive direction of X. 
     (Step 3) Travelling and Excavation in Positive Direction of Y 
     Next, a description will be given of steps of moving in the Y direction from the state of the (Step 2-5) of the (Step 2) described above. 
     (Step 3-1) When moving the mining station  220  in the Y direction from the state illustrated in (f) of  FIG. 31 , the base control unit  45  releases the four support legs  26  of the lower platform  21 Y from the seabed while keeping the support legs  26  of the upper platform  21 X landed. Then, the base control unit  45  moves the lower platform  21 Y fully in a positive direction of Y, as illustrated in (a) of  FIG. 32 , in the state where the upper platform  21 X and the middle frame  21 M are joined together. After that, the four support legs  26  of the lower platform  21 Y are landed. 
     (Step 3-2) After that, while keeping the support legs  26  of the lower platform  21 Y landed, the base control unit  45  releases the four support legs  26  of the upper platform  21 X from the seabed, and then, moves the upper platform  21 X and the middle frame  21 M fully in the positive direction of Y, as illustrated in (b) of  FIG. 32 , in the state where the upper platform  21 X is fixed to the middle frame  21 M. After that, the four support legs  26  of the upper platform  21 X are landed. 
     (Step 3-3) Next, while keeping the four support legs  26  of the upper platform  21 X landed, the base control unit  45  releases the four support legs  26  of the lower platform  21 Y from the seabed. Then, the base control unit  45  moves the lower platform  21 Y in the positive direction of Y to a position where a plane center of the lower platform  21 Y coincides with plane centers of the upper platform  21 X and the middle frame  21 M, as illustrated in (c) of  FIG. 32 , in the state where the upper platform  21 X and the middle frame  21 M are joined together. 
     After that, the base control unit  45  lands the four support legs  26  of the lower platform  21 Y. As a result, the predetermined region inside the upper and lower platforms  21 X and  21 Y becomes a fifth section E illustrated in  FIG. 23 . As illustrated in  FIG. 33 , in the fifth section E, the base control unit  45  receives a mining start command from the management computer, and then mines the predetermined region inside the middle frame  21 M. 
     (4) Repetition 
     Hereinafter, as illustrated in (a) to (c) of  FIG. 33 , when moving in a negative direction of X, the same steps as those in the positive direction of X may be performed in an opposite direction, and the operations of the (Step 2) and (Step 3) described above are repeatedly performed until excavation of the predetermined mining region (40×40 m) is completed. Additionally, regarding traveling in the X direction, the steps in the positive and negative directions of X may be executed alternately. 
     Thus, the mining station  220  of the third embodiment can correspond with the slopes and undulations of seabed ore deposits, as well as the mining station  220  capable of self-traveling can make it unnecessary to use the erection and installation mother ship  2 , which is a support ship for changing the position (relocation) of the mining station, or can significantly reduce situations requiring the use of the mother ship  2 . Thus, construction periods and cost for projects can be significantly reduced. 
     Note that while the above first embodiment has described the example of the erection and installation mother ship  2  that is a large vessel carrying the mineral lifting unit  4  and the plurality of mining stations  20 , as in  FIG. 1 , but the present invention is not limited thereto. For example, as illustrated in  FIGS. 34A to 34C , a small erection and installation mother ship  2  can be used. 
     The erection and installation mother ship  2  of the drawing has a ship hull having a rectangular frame shape in a plan view, and the ship hull are provided with floating bodies  2   f  on right and left sides thereof. At a center of the ship hull in a plan view is provided a rectangular moon pool  2   p , and a crane (i.e., machine  11 ) is straddled over the ship hull so as to stride over the moon pool  2   p.    
     On a deck of the ship hull are provided a living room  2   h  and a reservoir  2   s , and also a winch  11   w  is equipped at an appropriate place to allow the mining station  220  to be hung down in the sea and lifted up from the moon pool  2   p . Note that reference signs D and U in  FIG. 34C  represent an image in which the mining station  220  can be hung down and lifted up. 
     Note that, in terms of erection and installation of the mining station  220  of the third embodiment, it preferable to set dimensions of the erection and installation mother ship  2  to about 72 m in entire length and 48 m in entire width and dimensions of the moon pool  2   p  to about 30 m by 33 m. Using such a small erection and installation mother ship  2  is more preferable in terms of cost reduction, because the cost of the support ship itself, the cost of anchoring a ship at sea, and the like can be further reduced. 
     Herein, on seabed hydrothermal deposits, there are chimneys spouting hot water (chimney-like hot water spouting protrusions) on seamounts. Due to this, when erecting the mining station  20 ,  120 , or  220  of the above respective embodiments on a seabed and when performing walking operation of the mining station  120  or  220  of the second or third embodiment, it is necessary to prevent or suppress interference between the mining station and obstacles such as chimneys. Thus, hereinafter, a description will be given of a mining station including chimney monitoring means, a mining base monitoring device, and a chimney avoidance method. 
     In the mining station  220  of the third embodiment, the base control unit  45  is configured to include a chimney detecting unit  91 , as illustrated in  FIG. 35 . The chimney detecting unit  91  is chimney detection means configured to detect chimneys on seabed ore deposits. The chimney detecting unit  91  includes an ultrasonic wave transmitting and receiving unit  92  and a detection unit  93  configured to detect chimneys on the basis of an echo obtained by underwater detection using an ultrasonic wave. 
     The ultrasonic wave transmitting and receiving unit  92  emits an ultrasonic wave toward a seabed ore deposit from a base side, and then is immediately switched to a reception status to receive a reflection wave from the seabed ore deposit. The detection unit  93  measures a round trip time from the emission of the ultrasonic wave to the reception of the reflection wave, converts the round trip time into a distance to measure the distance from the mining station  220  to the chimney, and detects an interface state of the seabed ore deposit and the presence or absence of a chimney. 
     The chimney detection means illustrated in  FIG. 35  is searchlight type sonar (multi-beam sonar) in which a drive unit  90  is added to the chimney detecting unit  91 . The chimney detecting unit  91  is provided, for example, at a highest appropriate place in the center of the platform  21 , where while the chimney detecting unit  91  performs search at a viewing angle that is a predetermined angle, the drive unit  90  rotates the chimney detecting unit  91  by 360 degrees in the horizontal plane. This enables detection on the entire periphery of the mining station  220 . 
     Note that the place for arranging the chimney detecting unit  91  is not limited to the “highest appropriate place in the center of the platform  21 ”, and the chimney detecting unit  91  can be arranged at another position of the mining station  220  long as an intended search can be performed. For example, the chimney detecting unit  91  may be provided on a surface of the platform  21  facing an ore deposit side. In this case, it is possible to detect the unevenness of the ore deposit by measuring a height of a lower portion of the mining station  220  itself, including the support legs  26  and the guide shells  48 , and heights of its surrounding terrain, from the surface of the platform  21  facing the ore deposit side. 
     Note that the chimney detection means is not limited to searchlight type sonar, and, for example, scanning sonar may be used. Scanning sonar can detect the entire circumference of 360 degrees of the mining station  220  at one time. Additionally, while the mining station  220  of the third embodiment has been described as the example including the chimney detecting unit  91  using ultrasonic waves as the chimney detection means, the present invention is not limited thereto. Light may be used as the chimney detection means to detect chimneys. For example, the base control unit  45  can be configured to include an image processing unit for detecting chimneys on seabed ore deposits by camera or image sensor. 
     Furthermore, in the mining station  220  of the third embodiment, the base control unit  45  is configured to execute avoidance control to avoid a detected chimney. 
     Specifically, as illustrated in  FIG. 35 , the base control unit  45  is configured to be capable of monitoring torques of the motors driving the respective movement mechanisms described above by acquiring from detection values of respective torque detectors  52   x ,  44   y ,  47   z ,  71   r ,  9   p , Mx, My, and Mz ( 49 ) thereof. In addition, the base control unit  45  is configured to be capable of executing a program of chimney avoidance processing. 
     Note that, in the drawing, reference sign  52   x  denotes a torque detector attached to the motor of the X-direction movement mechanism  52 , reference sign  44   y  denotes a torque detector attached to the motor of the Y-direction movement mechanism  44 , reference sign  47   z  denotes a torque detector attached to the motor of the slide movement mechanism  47 , reference sign  71   r  denotes a torque detector attached to the rotating drive mechanism of the housing unit  71 , reference sign  9   p  denotes a torque detector attached to the drive unit of the high pressure water supply pump of the high pressure water supply pipe  9 , and reference signs Mx, My, and Mz ( 49 ) respectively denote torque detectors respectively attached to the X drive motors Mx, the Y drive motors My, and the motors of the jack mechanisms  49 . 
     Specifically, when the chimney avoidance processing is executed by the base control unit  45 , process proceeds to step S 21  as illustrated in  FIG. 36 . At step S 21 , motor torque is checked on the basis of the torque detectors attached to the X drive motors Mx and the Y drive motors My. When the torque is within a normal value range (Yes), the process proceeds to subsequent step S 22 . When the torque indicates an abnormal value, i.e., the monitored torque exceeds a predetermined value (No), it is determined that the corresponding movement mechanism has contacted with a chimney, and the process proceeds to step S 26 . 
     At step S 22 , the presence or absence of a command for avoidance from a mining base monitoring device  80  (e.g., manual operation by the operator) is confirmed, and if there is the avoidance command (Yes), the process returns to perform control in accordance with the avoidance command, whereas if there is no avoidance command (No), the process proceeds to subsequent step S 23 . 
     At step S 23 , echo image information detected by the chimney detecting unit  91  is acquired, followed by step S 24  where position information of chimneys detected by the chimney detecting unit  91  is acquired, and then, the process proceeds to step S 25 . At step S 25 , processing is performed to correlate position information of the mining station  220  itself with the position information of the chimneys. In the correlation processing, mutual interface information between position information of each portion of the mining station  220  itself and the position information of the chimneys is compared to calculate each relative distance. When the relative distance is closer than a predetermined threshold value, the corresponding chimney is determined to be an obstacle. 
     For example, when the chimney detecting unit  91  is equipped on the surface of the platform  21  facing the ore deposit side, it is possible to determine a height difference with respect to a set height of the platform  21  from position information of the support legs  26  and the guide shells  48 . Furthermore, an obstacle determination can be made from a moving direction of the mining station  220 . 
     At subsequent step S 26 , avoidance control is executed. The avoidance control is processing for avoiding a chimney determined to be an obstacle among detected chimneys. For example, when proceeded from step S 21 , control as a countermeasure for avoiding contact with an obstacle is performed, which control reversely drives a motor corresponding to any of the drive motors Mx and My whose monitored torque has been determined to have exceeded the predetermined value until the torque returns to within the normal value range. 
     In addition, for example, during excavation of the above-mentioned predetermined mining region (40×40 m), if there is a chimney that has been determined to be an obstacle in a section of the predetermined mining region, a bypass program for bypassing the corresponding section as a whole is executed as a countermeasure for avoidance at a time of non-contact with the obstacle, thereby avoiding the chimney determined as the obstacle. Alternatively, as a countermeasure for avoidance at the time of non-contact with the obstacle, walking processing of the mining station  220  itself may be suspended or controlled by a low-speed drive, and the process may proceed to step S 27  to wait for an instruction from the operator. 
     When waiting for an instruction from the operator, as the countermeasure for avoidance at the time of non-contact, the process proceeds to step S 27 , and detection information including the position information of the chimney determined to be the obstacle is output to the mining base monitoring device  80 . As a result, the operator monitoring by the mining base monitoring device  80  can take into consideration an image display, the interface information, the relative distance information, and the like on a display of the mining base monitoring device  80 , thereby enabling appropriate manual operation of the mining station  220 . 
     Herein, in a case where the operator performs a countermeasure for avoidance at the time of non-contact, it is preferable to manually avoid the chimney by measuring a terrain height from leg bottom information including the position information of the support legs  26  of the mining station  220  and the guide shells  48  to detect the unevenness of the ore deposit by, for example, the chimney detecting unit  91  on the bottom surface of the platform  21  and by referring to ultrasonic images and images captured by camera. 
     The reason that manual avoidance is preferable is that in general, an error obtained at measurement of a seabed base at a water depth of 2 km through sonar on the sea is about 20 m (1% of the water depth), and an assumed size of the mining station  220  is about 20 m. On the other hand, the chimney detecting unit  91  mounted on the mining station  220  has a resolution capability sufficient to detect chimneys. Thus, it may be difficult to perform correction processing when simply collating images simultaneously measured on the sea and on the seabed. Additionally, it may also be difficult to simply collate a detailed image (a map) obtained in advance near the seabed with the image measured on the seabed when the terrain has no outstanding characteristics. 
     Note that accuracy of measurement of the position and orientation of the mining station  220  is preferably improved by ultrasonic waves connecting the mining mother ship  1  serving as an offshore base or the erection and installation mother ship  2  to the mining station  220 , a gyro equipped in the mining station  220 , and additionally mounting of a depth meter. Alternatively, when lowering the mining station  220  in the sea from the offshore base, it is preferable to measure a lowering position by GPS and measure a route taken until it lands on the seabed by an inertial sensor mounted on the mining station  220 . At a movement step of walking on the seabed from a seabed landing start point, it is preferable to integrate from a mechanical movement amount and a moving direction of the seabed base. 
     At subsequent step S 28 , it is determined whether or not to re-acquire detection information. In other words, if a command for re-acquisition of detection information is input from the operator on the sea, the process returns to step S 21 . Otherwise, the process returns to main control processing. 
     Next, the mining base monitoring device will be described with reference to  FIGS. 37 and 38  as appropriate. 
     The mining base monitoring device  80  illustrated in  FIG. 37  corresponds to the above management computer equipped in the mining mother ship  1  serving as the offshore base or the erection and installation mother ship  2  to monitor the mining station  220 . Note that while the present embodiment has described the example where the mining base monitoring device  80  is equipped in the offshore base, the present invention is not limited thereto. The mining base monitoring device  80  can be equipped in a land base, and the monitoring operator can monitor not in the offshore base but in the land base distant therefrom. 
     As illustrated in  FIG. 37 , the mining base monitoring device  80  of the third embodiment is mining station position monitoring means configured to include a control unit  81 , a display unit  86 , an input unit  87 , and an undersea detecting device  82 , and also is chimney monitoring means. The control unit  81  includes software necessary for chimney monitoring processing and a computer that is a hardware resource configured to specifically execute information processing by the software. The control unit  81  is communicably connected to the base control unit  45  via the umbilical cable  8 , and also is connected to the display unit  86  such as a display and the input unit  87  such as a keyboard via signal lines so that necessary data communication is possible. The display unit  86  is configured to be capable of displaying the position information of the mining station  220  and the echo image of a chimney on a monitor screen. 
     The undersea detecting device  82  includes an ultrasonic wave transmitter  83  equipped in the mining station  220 , an ultrasonic wave receiver  84  equipped in three places of the ship bottom portion of the mining mother ship  1  or the erection and installation mother ship  2 , and a detecting unit  85 , and can obtain the position information of the mining station  220 , for example, by a technology similar to a Super Short Base Line (SSBL). 
     In performing chimney monitoring, when the operator performs a predetermined input operation from the input unit  87  of the mining base monitoring device  80 , chimney monitoring processing is executed. As illustrated in  FIG. 38 , the control unit  81  of the mining base monitoring device  80  first allows the process to proceed to step S 11 , where seabed map information of the corresponding sea region is read from a seabed map database stored in advance in a storage device or the like of the computer, followed by proceeding to step S 12 . At subsequent steps S 12  to S 13 , the echo image information of chimneys and the position information thereof detected by the chimney detecting unit  91  of the base control unit  45  are acquired (corresponding to the chimney information acquisition unit). 
     At subsequent step S 14 , undersea mining base position information including information on the posture of the mining station  220  and the like acquired from the base control unit  45  is acquired. Note that the base control unit  45  includes a three-dimensional gyro sensor, whereby the position information of the mining station  220  in the sea can be produced at any time, with reference to initial position information when the mining station  220  is hung down from the erection and installation mother ship  2  and on the basis of subsequent relative changes in the position of the mining station  220 . 
     Then, at step S 15 , on the basis of the acquired image information and position information of the chimneys and the position information of the mining station  220 , processing is performed to correlate with the seabed map information of the corresponding sea region. As a result, the position information of the mining station  220  and the echo images and position information of the chimneys are correlated with the seabed map information of the corresponding sea region. At subsequent step S 16 , images based on the correlated data are superimposed and displayed on the display unit  86  that is the monitor screen. 
     As a result, with the images superimposed and displayed on the display unit  86 , the operator can monitor the position and image picture of the mining station  220  in the sea and the positions and image pictures of the chimneys by visual checking (corresponding to the display synthesizing unit). The control unit  81  moves the seabed map and the echo image of the chimney superimposed and displayed on the display unit  86  in accordance with the movement of the mining station  220 . 
     In this manner, an image picture of the mining station  220  during walking acquired as needed can be always displayed on the display unit  86 . Note that the position information of the chimneys and the position information of the mining station  220  include latitude information and longitude information, and also include depth information of the chimneys and the mining station  220 . As a result, exploration with higher accuracy can be performed. Additionally, it is suitable in terms of accurately determining interface states. 
     Then, at subsequent step S 17 , obstacle determination processing is executed. In the obstacle determination processing, a chimney to be an obstacle to the mining station  220  is determined from the position information of the chimneys and the position information of the mining station  220  correlated together (corresponding to the determination unit). In the obstacle determination processing, among a plurality of chimneys displayed on the monitor screen of the display unit  86 , for example, a chimney closest to the mining station  220  is determined to be a chimney as an obstacle on the basis of the moving direction of the mining station  220 . 
     When the chimney is determined to be a chimney as an obstacle, for example, a warning display for calling the attention of the operator is provided, for example, by changing colors of a displayed image of the chimney from an ordinary color (e.g., blue) to a warning color (e.g., red), displaying the image of the chimney more brightly that the other chimneys, blinking the image thereof, or another way. 
     At subsequent step S 18 , the presence or absence of an input operation for a re-exploration demand from the input unit  87  by the operator is checked. If there is a re-exploration demand (Yes), the process returns to step S 12 . Otherwise (No), the process returns to step S 14 , and information other than the position information of the mining station  220  continues to be used. 
     Next, the chimney avoidance method will be described with reference to  FIGS. 39A, 39B, 40A and 40B . 
     As described above, in the third embodiment, the mining station  220  as the work device is configured so that the base control unit  45  includes the chimney detecting unit  91 , and the mining mother ship  1  or the erection and installation mother ship  2  includes the mining base monitoring device  80 . Thus, the structure of the third embodiment would enable avoidance of a chimney as an obstacle. 
     In other words, as described above, in the mining station  220 , the base control unit  45  executes the avoidance control to avoid a detected chimney. The chimney detecting unit  91  detects chimneys on a seabed ore deposit on the basis of an echo obtained by underwater detection by transmission and reception of ultrasonic waves (chimney detection step), and on the basis of position information of the detected chimneys, avoidance control to avoid a chimney determined to be an obstacle is executed. Thus, interference with the chimney to be an obstacle can be avoided (interference avoidance step). 
     Note that, as described in the avoidance control of step S 26 , when there is a chimney determined to be an obstacle in the section of a predetermined mining region, executing the bypass program for bypassing the corresponding section as a whole to avoid the chimney determined to be an obstacle enables ex-ante avoidance of interference with the chimney to be an obstacle, as illustrated in an image of ex-ante avoidance of  FIGS. 39A and 39B . Additionally, even when suspending the walking processing of the mining station  220  itself to wait for an instruction from the operator, interference with the chimney to be an obstacle can be avoided in advance. 
     On the other hand, even when ex-ante avoidance cannot be performed for some reason, the base control unit  45  monitors motor torques of the drive mechanisms including the drive motors Mx, My, and the like associated with walking, as described in the avoidance control of step S 26 , so that ex post avoidance of interference with the chimney to be an obstacle can be automatically performed. In other words, even when mining is performed under automatic control, not by an instruction from the operator, or even if the mining station  220  contacts with a chimney (an obstacle) due to erroneous manual operation by the operator, excessive collision with the chimney can be prevented or suppressed. 
     Specifically, as illustrated in an image of ex post avoidance of  FIGS. 40A and 40B , now assume a case where, in the drawing, during the movement of the lower platform  21 Y in the X direction (an arrow indicated by reference sign M represents an image of movement), the support leg  26  has contacted with a chimney C. 
     In this case, abnormal torque is generated in the Y drive motor My driving the lower platform  21 Y. Due to this, the torque detector of the Y drive motor My immediately outputs an abnormal value. As a result, the base control unit  45  determines that the movement mechanism corresponding to the Y drive motor My has contacted with the chimney (“No” at step S 21  of  FIG. 36 ), and performs avoidance control, whereby the corresponding Y drive motor My can be reversely driven until the torque of the Y drive motor My returns to within the normal value range (step S 26  of  FIG. 36 ). Thus, even when contact with a chimney occurs, excessive collision with the chimney can be prevented or suppressed. 
     Furthermore, the operator in the mining mother ship  1  or the erection and installation mother ship  2  allows the mining base monitoring device  80  to execute chimney monitoring processing. Thus, the mining base monitoring device  80  detects chimneys on a seabed ore deposit on the basis of an echo obtained by underwater detection through transmission and reception of an ultrasonic wave by the chimney detecting unit  91  (chimney detection step), and can display a seabed map on the display unit  86  that is the monitor screen, as well as can superimpose and display echo images of the mining station  220  and the chimneys, including display of obstacle determination, thereon. 
     As a result, the operator monitors the state of the mining station  220  in the sea as needed, and when it is determined on the basis of position information of detected chimneys that there is a chimney that may interfere with the mining station  220 , the operator can avoid the interference with the chimney as the obstacle in advance by manual operation (interference avoidance step). 
     Below is a list of reference numbers used in the drawings.
       1 : Mining mother ship (offshore mining base)     2 : Erection and installation mother ship     3 : Carrier ship     4 : Mineral lifting unit     5 : Suction pipe     6 : Mineral lifting pipe     7 : Discharge pipe     8 : Umbilical cable     9 : High pressure water supply pipe     10 : Mining device main body     11 : Work machine     12 : Power generator     13 : Reservoir     20 ,  120 ,  220 : Mining station (undersea mining base)     21 : Base frame (platform)     25 : Mineral lift pump     26 : Support leg     27 : Sizer     30 : Mining device     31 : Cylinder     32 : Water passage hole     33 : Cylinder liner     34 : Hammer     35 : Connecting member     36 : Cylinder bush     37 : Check valve     38 : Sleeve     39 : Ring     40 : Double pipe rod     41 : Cylinder front chamber     42 : Cylinder rear chamber     43 : Movement frame     45 : Base control unit (controller)     47 : Slide movement mechanism     48 : Guide shell     49 : Jack mechanism     50 : Bit     71 : Housing unit     80 : Mining base monitoring device     81 : Control unit     82 : Undersea detecting device     83 : Ultrasonic wave transmitter     84 : Ultrasonic wave receiver     85 : Detecting unit     86 : Display unit     87 : Input unit     90 : Drive unit     91 : Chimney detecting unit     92 : Ultrasonic wave transmitting and receiving unit     93 : Detection unit   SL: Sea level   SB: Seabed   OD: Ore deposit   VH: Pit (bottomed hole)