Patent Number: 
Section: claims

1. A robot for machining a part of structure under water, comprising:a machine tool having a submersible motor, a machining element coupled to the motor, a chamber receiving a driven portion of the machining element, and at least one gas inlet communicating with the chamber;a support and guiding structure for the machine tool, fixable with respect to the part to be machined and having submersible mobile elements and corresponding submersible guiding elements defining axes along which the mobile elements are movable for positioning the machine tool with respect to the part to be machined, the machine tool being attached to one of the mobile elements within reach of the part to be machined when the support and guiding structure is fixed with respect to the part to be machined, the mobile elements and the guiding elements having a rigidity resisting to stresses produced by the machine tool when the machine tool is in operation;displacement units for displacement of the mobile elements along the axes;a gas supply connectable to the at least one gas inlet of the machine tool for injecting gas in the chamber; anda control unit connecting to the machine tool and to the displacement units, the control unit being programmable for operating the displacement units and the machine tool based on a closed-loop control mode in order to perform the machining of the part. 2. The robot according to claim 1, wherein:the structure has structural elements between which the part to be machined extends; andthe support and guiding structure has a longitudinal axis in which one of the guiding elements called longitudinal guiding element extends, the robot further comprising attachments projecting at opposite ends of the longitudinal guiding element and operable to lock the support and guiding structure between the structural elements so that the longitudinal guiding element substantially extends in parallel to the part to be machined. 3. The robot according to claim 2, wherein the longitudinal guiding element comprises at least one longitudinal module having opposite ends configured to assemble with opposite ends of like modules used depending on whether a spacing between the structural elements requires more than one longitudinal module. 4. The robot according to claim 2, wherein each attachment comprises:an arrangement of shoes, two of which project in opposite directions and are mobile between extended and retracted positions in which, respectively, the shoes engage against and disengage from the corresponding structural element;articulated rods connected to the mobile shoes; anda jack coupled to the articulated rods and operable so that the articulated rods move the mobile shoes between the extended and retracted positions. 5. The robot according to claim 1, wherein the guiding elements called longitudinal, transverse and vertical guiding elements and the corresponding axes respectively extend in longitudinal, transverse and vertical directions of the support and guiding structure, one of the vertical and transverse guiding elements being attached to the mobile element corresponding to the longitudinal guiding element, and the other one of the vertical and transverse guiding elements being attached to the mobile element corresponding to said one of the vertical and transverse guiding element. 6. The robot according to claim 5, wherein:the longitudinal guiding element comprises an elongated lattice having a triangulation contributing to its rigidity, and a pair of parallel tracks projecting along the elongated lattice, the corresponding mobile element comprising a platform slideably mounted on the tracks; andthe displacement unit of the mobile element corresponding to the longitudinal guiding element comprises a submersible rotary motor having a pinion coupled to a rack extending in parallel to the longitudinal axis, the rack and the rotary motor being respectively mounted on one and the other one of the longitudinal guiding element and the corresponding mobile element. 7. The robot according to claim 5, wherein:the transverse and vertical guiding elements comprise respective housings and respective pairs of parallel tracks projecting along the corresponding housings, the corresponding mobile elements comprising respective platforms slideably mounted on the corresponding pairs of tracks; andthe displacement units for displacement of the mobile elements corresponding to the transverse and vertical guiding elements comprise submersible linear motors having respective magnetic shafts with permanent magnets extending in longitudinal directions of the respective housings, the motors and their magnetic shafts being respectively mounted on one and the other one of the mobile elements and the corresponding guiding elements. 8. The robot according to claim 5, wherein the displacement units comprise respective motors operationally coupled to the mobile elements and to the corresponding guiding elements to move the mobile elements along the axes in response to control signals generated by the control unit, and respective position encoders connecting to the control unit to produce position information of the mobile elements along the axes at the control unit, the closed-loop control mode comprising a control in position of the motors with respect to the position information produced by the position encoders. 9. The robot according to claim 8, wherein:the machine tool is attached to the mobile element corresponding to the vertical guiding element; andthe support and guiding structure further comprises an electrical box mounted on the vertical guiding element on a side opposite to the machine tool, the electrical box having watertight openings for receiving cables connecting the motors and the position encoders to the control unit. 10. The robot according to claim 1, wherein:the machining element comprises a grinding wheel;the machine tool comprises a guard defining the chamber, the guard having a lower opening through which a portion of the perimeter of the grinding wheel extends, and an inner surface extending close to the grinding wheel and having a shape adapted to the grinding wheel; andthe machine tool comprises a transmission coupling the grinding wheel to the motor, and an arrangement slideably supporting the guard with respect to the grinding wheel so that the guard draws back as the grinding wheel wears off. 11. The robot according to claim 10, wherein:the transmission comprises an adjustable transmission unit disposed in a housing defining an inner space;the machine tool comprises at least one extra gas inlet communicating with the inner space of the housing; andthe gas supply also connects to the at least one extra gas inlet to inject gas in the housing. 12. The robot according to claim 10, wherein the at least one gas inlet comprises a gas diffusing channel extending along the inner surface of the guard. 13. The robot according to claim 1, wherein:the control unit comprises:a computer;interface cards connecting to the computer;controllers having communication ports connecting to the interface cards, power supply inputs, controllable power outputs connecting to the displacement units and to the machine tool, electronic supply inputs, and feedback signal inputs connecting to the displacement units and to the machine tool;power converters having electric supply inputs, and power supply outputs connecting to the power supply inputs of the controllers; anda power supply unit having an electric supply input, and electronic supply outputs connecting to the electronic supply inputs of the controllers; andthe gas supply comprises a solenoid valve having a gas supply inlet, a communication port connecting to one of the interface cards, and a controllable gas outlet connecting to the machine tool. 14. The robot according to claim 13, wherein the computer is configured to store a map of the surface of the part to be machined, receive and process the feedback signals, and control the solenoid valve and the controllers based on the closed-loop control mode using the feedback signals, the map of the surface of the part to be machined, and programmable reconditioning parameters of the surface of the part to be machined. 15. The robot according to claim 13, wherein the feedback signals comprise position signals of the mobile elements with respect to the corresponding guiding elements, current signals of the displacement units, and speed and current signals of the machine tool. 16. The robot according to claim 1, wherein the part of structure to be machined comprises a runway, a sill or a lintel of a sluice. 17. A method for machining a part of structure under water with a machine tool having a submersible motor and a machining element coupled to the motor, comprising the steps of:fixing a support and guiding structure for the machine tool with respect to the part to be machined, the support and guiding structure having submersible mobile elements and corresponding submersible guiding elements defining axes along which the mobile elements are movable, and displacement units for displacement of the mobile elements along the axes for positioning the machine tool with respect to the part to be machined, the machine tool being attached to one of the mobile elements within reach of the part to be machined when the support and guiding structure is fixed with respect to the part to be machined, the mobile elements and the guiding elements having a rigidity resisting to stresses produced by the machine tool when the machine tool is in operation;providing the machine tool with a chamber receiving a driven portion of the machining element, and at least one gas inlet communicating with the chamber;supplying the at least one gas inlet of the machine tool with gas for injecting gas in the chamber; andoperating the displacement units and the machine tool based on a closed-loop control mode in order to perform the machining of the part.