Submersible robot for operating a tool relative to a surface of an underwater structure

FIELD OF THE INVENTION

0001The present invention generally relates to works relative to an underwater structure, and more particularly to a submersible robot for operating a tool relative to a surface of an underwater structure. The targeted structure may be one of the embedded parts present on hydroelectric works, in particular a runway, seal seat, sill or lintel of a sluice.

BACKGROUND

0002The runways, the seal seats, the sill or the lintel of a sluice, in a hydroelectric work, are used to receive a gate or stop logs in order to block and seal the opening in a dam. Its structures are prone to wear as time passes and thus requiring restoration works in order to preserve their functionalities. The traditional underwater structure restoration methods are based on minor repair tasks that may be completed under water by experimented divers and also on major works that require the preliminary installation of a cofferdam in order to dry the work area.

0003The automated underwater restoration exhibits economical advantages, but raises serious technical problems due to the design of the submersible systems comprising various electromechanical parts. Other problems arise to both ensure automated and remotely operated tasks in an underwater environment, where the human presence is considered dangerous, where the visibility is reduced and the availability of the required sensors is limited. The underwater enviromnent is also a source of important perturbations that may affect the operation of the sensors, the manipulators and other actuators. The control of the machining process is also affected by the underwater environment and poses precision and repetitiveness problems. Furthermore, it is necessary for certain works to perform the restoration in different time windows having variable durations. To optimize the restoration time and allow respecting these time windows, the installation and uninstallation time in the work area must be as short as possible, which implies that it is important to reduce the amount and volume of the equipment to be installed to its minimum, as well as to simplify the complexity of the installation and the number of steps to be followed.

0004Some apparatuses allowing performing works under water have already been proposed.

0005For example, U.S. Pat. No. 6,309,147 (Matsumoto et al.) shows a remotely operated tool for drilling a plate in a nuclear reactor vessel. The tool has a drill bit moving along its rotation axis inside a stationary sleeve. The tool is mounted over the plate to be drilled, and a system is provided for collecting the chips resulting from the drilling. The drilling requires that the tool be still and properly fixed with respect to the plate to be drilled, and thus has no lateral or transverse mobility for its displacement, nor vertical other than that relative to the drill bit as required for the drilling. Furthermore, the tool is only provided with a basic controller limited to the operation of the motors of the tool and not designed to have automation capabilities for the drilling task, and even less for other tasks.

0006U.S. Pat. No. 6,555,779 (Obana et al.) proposes an apparatus that prevents water from entering in a bell covering and sliding on a workpiece, for example for welding or cutting. The apparatus has a pressurized water or gas injection system intended to form a water or gas curtain around the periphery of the bell to prevent water from entering. The apparatus is especially designed for performing a welding task along a line and can be mounted on a track by means of an assembly subjected to no important stresses and having a consequent construction. The control of the welding task is achieved by remote control operations from a worker, or by an automated mechanism reacting to image data captured with a camera during the welding.

0007U.S. Pat. No. 5,377,238 (Gebelin et al.) proposes a device for cutting or grinding a support of a nuclear reactor fuel assembly. The configuration of the device is specifically adapted to the prismatic geometry of the fuel assembly, and thus has a platform horizontally fastening to a support of the fuel assembly, a mobile carriage mounted on the platform, a hoist for hoisting the assembly, clamping elements for immobilizing the assembly, a table mounted on the carriage with a return element, a tool support mounted on the table, and a tool secured to the tool support.

0008JP application 2005297090 (Sato et al.) proposes a device for underwater polishing of a workpiece and collecting chips without however requiring a suction pump. The device comprises impellers disposed on the rotation shaft of the tool located in a bell so as to produce a negative pressure in the bell for draining the chips and water towards a filter that collects the chips. The construction of the device only allows light polishing or grinding works

0009In general, the prior art apparatuses and devices have automation, mobility, portability, installation, robustness, stiffness, precision and/or adaptation capabilities limited to such an extent that they are not adapted to the automation and achievement of intensive machining or measurement works under water, as for the milling of embedded parts of hydro-electric structures. This case of milling involves important stresses and vibrations at the level of the manipulator of the milling tool and requires a good global stiffness.

SUMMARY

0010An object of the invention is to provide a submersible robot for operating a tool relative to a surface of an underwater structure, like one of the embedded parts present on hydro-electric works, in particular runways, seal seats, the sill or the lintel of a sluice used to receive gates and stop logs.

0011Another object of the invention is to provide such a robot that is apt to achieve machining tasks and in particular surfacing, face milling, plunge milling, slotting, ramping, contour milling, 3D machining, drilling, boring, spot facing or tapping of parts of various sizes.

0012Another object of the invention is to provide such a robot that can operate by using a combination of relative reference in relation to the structure to be machined, without using an added referencing support structure.

0013Another object of the invention is to provide such a robot that may measure the surface with precision, before and after a machining task.

0014Another object of the invention is to provide such a robot that has short installation and uninstallation times compared to the prior art apparatuses.

0015Another object of the invention is to provide such a robot that can stand still in relation to the structure to be machined, without using an added support structure.

0016According to one aspect of the present invention, there is provided a submersible robot for operating a tool relative to a surface of an underwater structure, comprising: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0017">a support assembly;</li><li id="ul0002-0002" num="0018">a tool holder for holding the tool in operative position relative to the surface of the structure, the tool holder being movably mounted on the support assembly so that the tool is movable in a work area relative to the surface of the underwater structure when the tool is mounted on the tool holder;</li><li id="ul0002-0003" num="0019">a driving arrangement mounted on the support assembly for moving the tool holder so that the tool is movable within the work area when the tool is mounted on the tool holder;</li><li id="ul0002-0004" num="0020">a locking arrangement mounted on the support assembly for locking a position of the support assembly relative to the surface of the underwater structure;</li><li id="ul0002-0005" num="0021">a levelling arrangement mounted on the support assembly for adjusting an orientation of the support assembly relative to the surface of the underwater structure when the support assembly is locked by the locking arrangement;</li><li id="ul0002-0006" num="0022">a sensor unit directable toward the surface of the underwater structure, for measuring a distance between the robot and the surface of the underwater structure; and</li><li id="ul0002-0007" num="0023">a programmable control unit mounted on the support assembly for operating the driving arrangement, the locking arrangement, the levelling arrangement and the tool and receiving measurements from the sensor unit, the programmable control unit having an operation mode wherein a positioning of the robot relative to the surface of the structure is determined and controlled as function of an initial position of the robot for defining a first work area, and shifted positions of the robot for defining additional work areas, the work areas having overlapping portions with one another for tracking displacements of the robot relative to the surface of the underwater structure using the sensor unit.</li></ul></li></ul>

0024Preferably, the robot is connected to a control station above water surface via an umbilical cable. The control station may comprise power supplies, monitors and a computer that produces and transmits control signals to the robot and provides a user interface.

0025An electromagnetic clutch may be used for coupling the tool holder to a motor mounted on the support assembly for driving the tool. The robot may be provided with a suction nozzle located close to the tool and coupled to a flexible pipe connected to a submersible pump, allowing the suction of dust and chips produced by the tool and possibly their recovery and filtration at the pump outlet.

0026The robot may be provided with a submersible camera possibly reduced in size, positioned to view the tool.

0027The support assembly may be made of frame members advantageously usable to perform large machining works.

0028The locking and levelling arrangements may have a configuration allowing the holding, the locking and the positioning of the robot in a slot facing the section of the surface to be worked or inspected.

BRIEF DESCRIPTION OF THE DRAWINGS

0029A detailed description of preferred embodiments will be given herein below with reference to the following drawings:

0030<figref idref="DRAWINGS">FIG. 1</figref> is a schematic diagram of a submersible robot according to the invention, in position inside a dam gate slot, for achieving a milling task for the restoration of a seal seat.

0031<figref idref="DRAWINGS">FIG. 2</figref> is a schematic close-up diagram of the robot positioned in the slot shown in <figref idref="DRAWINGS">FIG. 1</figref>.

0032<figref idref="DRAWINGS">FIG. 3</figref> is a schematic diagram of the submersible robot according to the invention.

0033<figref idref="DRAWINGS">FIG. 4</figref> is a schematic diagram of two frame members of a support assembly for a milling tool, a laser measurement sensor, a suction nozzle and a mini-camera according to the invention, allowing displacements in a plane perpendicular to the milling tool.

0034<figref idref="DRAWINGS">FIGS. 5A and 5B</figref> are schematic top and bottom view diagrams of the second frame member of the support assembly for the milling tool.

0035<figref idref="DRAWINGS">FIG. 6</figref> is a schematic diagram of a support and guiding structure for a levelling foot according to the invention.

0036<figref idref="DRAWINGS">FIG. 7</figref> is a schematic control diagram of the robot according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0037As used in connection with this disclosure, the term “underwater structure” comprises a structure that may be fully or partially immerged or submerged.

0038Referring to <figref idref="DRAWINGS">FIG. 1</figref>, there is shown a submersible robot <b>2</b> according to the invention, in position inside a dam gate slot <b>4</b>, for achieving a milling task for the restoration of a runway <b>6</b> (or seal seat) of an underwater dam structure <b>8</b>. The following description of the robot <b>2</b> is made with reference to such a task. It should however be understood that the robot <b>2</b> is not limited to such a task and may be used for milling a sill <b>10</b> or lintel <b>11</b> of a sluice or other embedded parts of a hydroelectric work, or for performing other tasks, on other kinds of underwater structures. In <figref idref="DRAWINGS">FIG. 1</figref>, the robot <b>2</b> is positioned for milling the surface of the runway <b>6</b>. It can be inverted for milling the surface of the part <b>6</b>′ opposite to the runway <b>6</b>.

0039Installation of the robot <b>2</b> can be achieved by placing it above the slot <b>4</b> and subsequently lowering it inside the slot <b>4</b> by means of a cable <b>12</b> using a hoisting system like a winch, a bridge crane, etc. (not shown) in order to roughly position the robot <b>2</b> at the desired vertical distance from the upper surface <b>14</b> of the slot <b>4</b>. The robot <b>2</b> is then lowerable along the runway <b>6</b> down to the lowermost point formed by the sill <b>10</b>. The electrical supply and the control of the robot <b>2</b> may be achieved through an umbilical cable <b>16</b> from a control station <b>18</b> located above water level. The umbilical cable <b>16</b> may combine power and communication conductors (not shown) and a gas supply pipe (not shown). The conductors and the pipe may be separated from one another if desired.

0040Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the robot <b>2</b> can be fastened to the cable <b>12</b> by means of a fastening arrangement <b>20</b>. The robot <b>2</b> has a support assembly <b>22</b> having an opening <b>24</b> through which the surface of the runway <b>6</b> can be machined.

0041Referring to <figref idref="DRAWINGS">FIG. 3</figref>, the support assembly <b>22</b> has an elongated frame <b>23</b> and two mobile members <b>24</b>, <b>26</b> moveably mounted on respective guiding members such as pairs of tracks <b>38</b> (only the tracks <b>38</b> for the mobile member <b>24</b> can be seen in the Figure) that respectively define Y and X axes along which the mobile members <b>24</b>, <b>26</b> can be moved, in order to position a tool holder <b>42</b> with respect to the surface to be machined. The tracks <b>38</b> can be provided with stops <b>40</b> at opposite ends. Displacement of the mobile members <b>24</b>, <b>26</b> can be achieved using corresponding driving mechanisms, for example rack and pinion systems (detailed hereinafter) in parallel with the pairs of tracks <b>38</b>, coupled to motors <b>58</b>, <b>60</b>.

0042The support assembly also has levelling legs <b>28</b>, <b>30</b>, <b>32</b> and <b>60</b> two thrust pistons <b>34</b>, <b>36</b> (or jacks) for locking the support assembly <b>22</b> in operative position with respect to the surface to be machined. The pistons <b>34</b>, <b>36</b> are preferably linked with each other by a transverse member <b>44</b> for rigidity purposes. The pistons <b>34</b>, <b>36</b> can be operated using the gas supply in the umbilical cable <b>10</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref>). With appropriate gas pressure, both pistons <b>34</b>, <b>36</b> extend so that their feet <b>46</b>, <b>48</b> press against the surface <b>6</b>′ opposite to the surface <b>6</b> to be machined. As a result, the pistons <b>34</b>, <b>36</b> cause a counteraction on the levelling legs <b>28</b>, <b>30</b>, <b>32</b>, so that the robot <b>2</b> is held in position by friction inside the slot <b>4</b> (shown in <figref idref="DRAWINGS">FIG. 2</figref>) with five pressure points. A camera support <b>50</b> can be secured to the transverse member <b>44</b> in order to support and direct a camera <b>53</b> for viewing the displacement of the mobile members <b>24</b>, <b>26</b>.

0043The robot <b>2</b> has a watertight enclosure <b>52</b> containing electric and electronic components forming an onboard control unit <b>128</b> (shown in <figref idref="DRAWINGS">FIG. 7</figref>). The enclosure <b>52</b> is connectable to the umbilical cable <b>16</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref>) and to other sensor and actuator cables (not shown) of the robot <b>2</b>. The cables going toward the mobile members <b>24</b>, <b>26</b> preferably pass through flexible cable guides <b>54</b>, <b>56</b> that protect the cables and allow fluid movement of the mobile members <b>24</b>, <b>26</b>. The onboard control unit <b>128</b> is programmable and allows operating the motors <b>58</b>, <b>60</b> and possibly a motor <b>62</b> for operating the tool <b>92</b> (shown e.g. in <figref idref="DRAWINGS">FIG. 4</figref>). The control unit <b>128</b> may be configured to perform the machining task according to an open loop control mode, with trajectory monitoring. A closed loop control mode may also be used if desired.

0044The robot <b>2</b> may be provided with a pump <b>64</b> preferably extending outside the slot <b>4</b> (shown in <figref idref="DRAWINGS">FIG. 2</figref>) and attached to the enclosure <b>52</b> for example by a tightening clamp <b>66</b>. The pump <b>64</b> is connectable to a suction nozzle <b>68</b> (shown in <figref idref="DRAWINGS">FIG. 5B</figref>) on the tool holder <b>42</b> through a flexible hose or pipe <b>70</b>. for suction of the dust and chips produced during the milling task. The chips can be filtered and/or collected at the outlet of the pump <b>64</b> or discharged at the surface for subsequent processing.

0045The robot <b>2</b> may be fastened to the cable <b>12</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref>) using one of the fastening arrangements <b>20</b>, <b>20</b>′ provided at the opposite ends of the support assembly <b>22</b>, depending on the surface <b>6</b>, <b>6</b>′ of the slot <b>4</b> (shown in <figref idref="DRAWINGS">FIG. 2</figref>) to be machined. In the illustrated case of <figref idref="DRAWINGS">FIG. 2</figref>, the fastening arrangement <b>20</b> is used for milling the surface <b>6</b>. The fastening arrangement <b>20</b>′ would then be used for milling the surface <b>6</b>′.

0046The robot <b>2</b> preferably has a modular configuration so that it can be adapted to different sizes of slots by modifying the arrangement, positions and sizes of its mechanical parts, and the arrangement and positions of its sensors and actuators.

0047Referring to <figref idref="DRAWINGS">FIG. 4</figref>, the mobile member <b>24</b> has two pairs of guiding shoes <b>72</b> (only one shoe <b>72</b> of a pair is apparent in the Figure, the other shoe of the same pair being hidden behind the motor <b>58</b> whereas the shoes of the other pair are respectively hidden by the tool holder <b>42</b> and the mobile member <b>26</b>) slideably mounted on the tracks <b>38</b> (shown in <figref idref="DRAWINGS">FIG. 3</figref>). The rack and pinion system used to move the mobile member <b>24</b> in the Y axis may be formed of a precision pinion <b>74</b> coupled to the motor <b>58</b> and engaging with a rack (not shown) extending on the support assembly <b>22</b> (shown in <figref idref="DRAWINGS">FIG. 3</figref>) in the Y direction. The motor <b>58</b> may be a hybrid stepping motor with an integrated reducer. Induction or other types of proximity sensors <b>76</b> may be mounted near ends of the guiding shoes <b>72</b> to detect the stops <b>40</b> (shown in <figref idref="DRAWINGS">FIG. 3</figref>) for limiting the displacement of the mobile member <b>24</b>.

0048Tracks <b>78</b> can be mounted on the member <b>24</b> for guiding the member <b>26</b> in the X axis in order to position the tool holder <b>42</b> with respect to the surface to be machined. A rack <b>80</b> in parallel with one of the tracks <b>78</b> can be used to move the member <b>26</b>.

0049Referring to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>, the member <b>26</b> has two pairs of guiding shoes <b>82</b>, <b>84</b> (better shown in <figref idref="DRAWINGS">FIG. 5B</figref>) slideably mounted on the tracks <b>78</b> (shown in <figref idref="DRAWINGS">FIG. 4</figref>). The rack and pinion system used to move the mobile member <b>26</b> in the X axis may be formed of a precision pinion <b>88</b> coupled to the motor <b>60</b> and engaging with the rack <b>80</b> (shown in <figref idref="DRAWINGS">FIG. 4</figref>). The motor <b>60</b> may be a hybrid stepping motor with an integrated reducer.

0050Depending on the tool to be used by the robot <b>2</b>, the tool holder <b>42</b> may be provided with a tool bearing mechanism <b>90</b> to which the tool <b>92</b> can be secured in a possibly rotatable manner. The tool holder <b>42</b> may also be used to support an optional camera <b>94</b>, the suction nozzle <b>68</b> coupled to the flexible pipe <b>70</b> (shown in <figref idref="DRAWINGS">FIG. 3</figref>), and a sensor <b>96</b>. The camera <b>94</b> may be used to view the working area of the tool <b>92</b>. The sensor <b>96</b> may be positioned close to the tool <b>92</b> and arranged to perform a relative distance measurement between a reference point of the robot <b>2</b> and a corresponding point on the surface to be machined. The sensor <b>96</b> may be a laser sensor so as to obtain a good resolution and measurement precision, without contact with the surface to be machined underwater. However, other types of sensors may be used if desired provided that the precisions required for performing the machining task are satisfied.

0051The tool <b>92</b> may be driven in rotation by a sprocket wheel <b>98</b> driven by another sprocket wheel <b>100</b> through a sprocket belt <b>102</b> (better shown in <figref idref="DRAWINGS">FIG. 5B</figref>) whose tension is controlled by a tightener <b>104</b>. The tool bearing mechanism <b>90</b> then rotatably supports the tool <b>92</b> and transmits rotation of the sprocket wheel <b>98</b> to the tool <b>92</b>. The wheel <b>100</b> may be coupled to the motor <b>62</b> through a magnetic coupling clutch mechanism <b>106</b> for transmitting rotation of the motor <b>62</b> to the sprocket wheel <b>100</b>. Other types of coupling mechanisms may be used if desired, and a direct drive configuration may also be used to drive the tool <b>92</b> to simplify the driving arrangement if desired, for example depending on the size and power of the motor <b>62</b>.

0052Referring to <figref idref="DRAWINGS">FIG. 6</figref>, there is shown a possible construction for the levelling legs <b>28</b>, <b>30</b>, <b>32</b>. A levelling foot <b>108</b> slideably projects under a housing <b>110</b>. The foot <b>108</b> is connected to a linear actuator made of an ACME screw assembly having a shaft <b>112</b> with a longitudinal keyway coupled to a rotatable nut <b>114</b>. The nut <b>114</b> forms a toothed pulley coupled to a driving toothed pulley <b>118</b> through a belt <b>116</b> provided with a tightener <b>122</b>. The driving pulley <b>118</b> is driven by a motor <b>120</b>, e.g. a hybrid stepping motor with integrated reducer. Lowering and raising of the foot <b>108</b> is achieved by operating the motor <b>120</b> in one direction or the other so that rotation of the driving pulley <b>118</b> is transmitted to the pulley-like nut <b>114</b> by the belt <b>116</b>, and rotation of the nut <b>114</b> is converted into a linear motion of the shaft <b>112</b> to which the foot <b>108</b> is connected. A proximity sensor <b>124</b> e.g. of an inductive type may be mounted on the housing <b>110</b> to detect a metal hook <b>126</b> projecting at an upper end of the shaft <b>112</b> in order to limit a farthest course of the foot <b>108</b> under the housing <b>110</b>.

0053Referring back to <figref idref="DRAWINGS">FIG. 3</figref>, the foregoing construction of the robot <b>2</b> allows it to be used in a water depth of at least 30 meters. The mechanical structure of the members <b>24</b>, <b>26</b> and their associated components ensures a rigidity supporting the milling efforts for restoring steel or other structures. The number of degrees of freedom and mobile parts is minimal in order to perform the required movements for a machining task, and the rigidity of each part of the support assembly <b>22</b> is adapted to the efforts to which it is subjected to. The positioning capacities of the robot <b>2</b>, through the precise measuring devices and the appropriate rigidity, combined with a control strategy with trajectory verification, allows achieving a milling or other similar machining task in an automated manner and with precision.

0054The five degrees of freedom of the robot <b>2</b> allows, with respect to the tool <b>92</b> (shown in <figref idref="DRAWINGS">FIG. 4</figref>), a X axis translation resulting from the displacement of the mobile member <b>26</b>, a Y axis translation resulting from the displacement of the mobile member <b>24</b>, and a Z axis translation (perpendicular to the X-Y plane) resulting from the combined displacement of the three levelling legs <b>28</b>, <b>30</b>, <b>32</b> and two rotations (one around the X axis, another one around the Y axis) resulting from the displacement of one or two levelling legs <b>28</b>, <b>30</b>, <b>32</b> while the third one remains fixed.

0055For a precise positioning of the robot <b>2</b> for example for restoring an embedded part on its whole length, an overlap based positioning method may be used. Such a method allows global referencing of the robot <b>2</b> with respect to a reference point such as a point located in an upper portion of the slot <b>4</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref>) out of the water. The method uses a starting reference point and local references between every displacements of the robot <b>2</b> in order to find a relative position with respect to a previous position to determine a current position of the robot <b>2</b> by computations.

0056Referring to <figref idref="DRAWINGS">FIG. 1</figref>, the positioning method may proceed as follows.

00571. From the surface, using the cable <b>12</b>, the robot <b>2</b> is vertically positioned in the slot <b>4</b> in front of the first section to be machined, engageable through the slot opening. A lower portion of the robot <b>2</b> may be submerged while an upper portion of the robot <b>2</b> remains out of the water.

00582. Pneumatic pressure is turned on to actuate the pistons <b>34</b>, <b>36</b> in order to lock the robot <b>2</b> in the slot <b>4</b>.

00593. Two mirror references located on the upper portion of the robot <b>2</b> are referenced outside the water using a precision laser tracker (not shown). For more precision, both references may be as far as possible from each other in the X and Y axes. With the displacements of each levelling legs <b>28</b>, <b>30</b>, <b>32</b> (shown in <figref idref="DRAWINGS">FIG. 3</figref>), the orientation (rotation) of the X and Y axes of the robot <b>2</b> is adjusted until the X-Y plane required for the restoration is reached. The robot <b>2</b> is then initialized at its zero machine point.

00604. The machining operation is performed on the current machining area using X, Y and Z translation movements as provided by the robot <b>2</b>. A trajectory algorithm may be used to compensate small deviations in rotation in the Z axis that may occur (Arz). Optionally, the sensor <b>96</b> (shown in <figref idref="DRAWINGS">FIG. 4</figref>) may carry out a complete or partial scan of the surface before and/or after the machining operation.

00615. The pneumatic pressure is turned off to release the pistons <b>34</b>, <b>36</b> to allow vertical movements of the robot <b>2</b> in the slot <b>4</b>.

00626. The robot <b>2</b> is lowered in the slot <b>4</b> about 90% of its effective machining vertical range (for a 1 m range, the robot <b>2</b> would be lowered about 900 mm). In other words, the robot <b>2</b> is lowered so as to reach the next section to be machined while preserving about 10% of the section previously machined (e.g. initially in the upper portion of the slot <b>4</b>). If the bottom of the slot <b>4</b> is reached, this will be the last machined section.

00637. The pneumatic pressure is turned on to actuate the pistons <b>34</b>, <b>36</b> to lock the robot <b>2</b> in the slot <b>4</b> for the new machining task.

00648. The 10% overlapping surface restored during the last machining operation is measured with the sensor <b>96</b> (for a robot with a 1 m range, the overlapping surface has a 100 mm height). Using vision algorithms, the shifts Δtx, Δty, Δtz, Δrx, Δry, Δrz resulting from the last displacement of the robot <b>2</b> may be correctly obtained as a function of the precision of the measurements carried out. Optionally, other sensors like inclinometers (not shown) on the robot <b>2</b> may be coupled to the algorithms to reduce possible detection errors.

00659. The orientation (rotation) of the X and Y axes of the robot <b>2</b> is adjusted until the X-Y plane required for the restoration is reached. This plane corresponds to the continuity of the plane obtained during the last machining operation.

006610. Return to step 4.

0067Other positioning methods may be used when the machining is not to be achieved on all the length of the underwater structure in a constant manner. The basic principle remains the same but the steps, the algorithms and the computations to be carried out may be different.

0068Referring to <figref idref="DRAWINGS">FIG. 7</figref>, there is shown a schematic simplified control diagram of the robot <b>2</b>. The onboard control unit <b>128</b> in the watertight enclosure <b>52</b> controls motor drives <b>130</b> connected to the motors <b>60</b>, <b>58</b>, <b>28</b>, <b>30</b>, <b>32</b> and <b>62</b>. The onboard control unit <b>128</b> communicates with the measurement sensor unit <b>96</b> to receive the distance data computed by the sensor. The onboard control unit <b>128</b> also receives proximity alert signals from the proximity sensors <b>76</b>, <b>77</b> and <b>124</b>, in order to detect the end of each axis. For the Z axis, only the lower end as been chosen to be detected. The control station <b>18</b> has a user interface monitor <b>132</b>, a user interface computer <b>134</b>, an electronics power supply unit <b>136</b> and a motors power supply unit <b>138</b>. The umbilical cable <b>16</b> connects the control station <b>18</b> with the watertight enclosure <b>52</b>. The electronics power supply unit <b>136</b> provides the supply to the onboard control unit <b>128</b>, the proximity sensors <b>76</b>, <b>77</b>, <b>124</b>, the measurement sensor unit <b>96</b> and possibly the cameras <b>53</b>, <b>94</b> through the umbilical cable <b>16</b>. The video signals from the cameras <b>53</b>, <b>94</b> can be transmitted through the umbilical cable <b>16</b> to the user interface computer <b>134</b> or to a separate monitoring unit (not shown) if desired. The motors power supply unit <b>138</b> provides the supply to the motor drives <b>130</b> through the umbilical cable <b>16</b>. The user interface computer <b>134</b> has a bidirectional communication link with the onboard control unit <b>128</b> also through the cable <b>16</b>. A video signal from the user interface computer <b>134</b> is sent to the user interface monitor <b>132</b>.

0069While embodiments of the invention have been illustrated in the accompanying drawings and described above, it will be evident to those skilled in the art that modifications may be made therein without departing from the invention. For example, the support assembly <b>22</b>, the mobile members <b>24</b>, <b>26</b>, the tool bearing mechanism <b>90</b>, the magnetic coupling mechanism <b>106</b> and the housing <b>110</b> may be constructed differently, as long as their constructions are submersible, have rigidities resisting to the direct and indirect efforts produced by the tool <b>92</b>, and fulfill functions similar to those described above. The motors <b>120</b> of the legs <b>28</b>, <b>30</b>, <b>32</b>, the motors <b>58</b>, <b>60</b> for moving the mobile members <b>24</b>, <b>26</b>, and the thrust pistons <b>34</b>, <b>36</b> contribute to the precision of the displacements of the tool <b>92</b> and provide an appropriate displacement and positioning range for the tool <b>92</b> with respect to the target surface for a machining task or another similar task. The motors <b>120</b>, <b>58</b>, <b>60</b> may be of different types and constructions if desired, as long as they allow the required positioning of the mobile elements <b>24</b>, <b>26</b>, <b>28</b>, <b>30</b>, <b>32</b>. The motors <b>120</b>, <b>58</b>, <b>60</b> can be optionally provided with braking mechanisms (not shown) for increased safety. Additional stops and sensors (not shown) may be provided for redundancy and increased safety. The proximity sensors <b>76</b>, <b>124</b> may be positioned otherwise and be of other types if desired.

0070It is possible to use the robot <b>2</b> in other configurations, for example for vertical or horizontal displacement on a structure of any kind without using the structure for referencing purposes, but only for replacing the cable <b>12</b> providing from the hoisting system at the surface. The locking arrangement of the robot <b>2</b> in the slot <b>4</b> with respect to the target surface may have another design depending on the configuration of the underwater structure. For example, the locking arrangement may be designed to squeeze a beam or a like member (not shown) extending near the target surface of the underwater structure.

0071The robot <b>2</b> may also be used to perform measurement, restoration or reconditioning works of an immerged structure in a dam, a ship harbor, a borehole, a bridge structure, or a ship hull.