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

A submersible robot for operating a tool relative to a surface of an underwater structure has a tool holder movably mounted on a support assembly provided with a driving arrangement for movably holding the tool in operative position relative to the surface. Position and orientation of the support assembly relative to the surface is locked and adjusted by locking and leveling arrangements. A programmable control unit operates the driving, locking and leveling arrangements and the tool and receives measurements from a sensor unit. The control unit has an operation mode wherein a positioning of the robot is determined and controlled as function of an initial position 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 structure using the sensor unit.

FIELD OF THE INVENTION

The 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

The 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.

The 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 environment 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.

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

For 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.

U.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.

U.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.

JP 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

In 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 hydroelectric 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

An 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 hydroelectric works, in particular runways, seal seats, the sill or the lintel of a sluice used to receive gates and stop logs.

Another 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.

Another 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.

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

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

Another 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.

According 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:a support assembly;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;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;a locking arrangement mounted on the support assembly for locking a position of the support assembly relative to the surface of the underwater structure;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;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; anda 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.

Preferably, 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.

An 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.

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

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

The 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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

Referring toFIG. 1, there is shown a submersible robot2according to the invention, in position inside a dam gate slot4, for achieving a milling task for the restoration of a runway6(or seal seat) of an underwater dam structure8. The following description of the robot2is made with reference to such a task. It should however be understood that the robot2is not limited to such a task and may be used for milling a sill10or lintel11of a sluice or other embedded parts of a hydroelectric work, or for performing other tasks, on other kinds of underwater structures. InFIG. 1, the robot2is positioned for milling the surface of the runway6. It can be inverted for milling the surface of the part6′ opposite to the runway6.

Installation of the robot2can be achieved by placing it above the slot4and subsequently lowering it inside the slot4by means of a cable12using a hoisting system like a winch, a bridge crane, etc. (not shown) in order to roughly position the robot2at the desired vertical distance from the upper surface14of the slot4. The robot2is then lowerable along the runway6down to the lowermost point formed by the sill10. The electrical supply and the control of the robot2may be achieved through an umbilical cable16from a control station18located above water level. The umbilical cable16may 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.

Referring toFIG. 2, the robot2can be fastened to the cable12by means of a fastening arrangement20. The robot2has a support assembly22having an opening24through which the surface of the runway6can be machined.

Referring toFIG. 3, the support assembly22has an elongated frame23and two mobile members24,26moveably mounted on respective guiding members such as pairs of tracks38(only the tracks38for the mobile member24can be seen in the Figure) that respectively define Y and X axes along which the mobile members24,26can be moved, in order to position a tool holder42with respect to the surface to be machined. The tracks38can be provided with stops40at opposite ends. Displacement of the mobile members24,26can be achieved using corresponding driving mechanisms, for example rack and pinion systems (detailed hereinafter) in parallel with the pairs of tracks38, coupled to motors58,60.

The support assembly also has levelling legs28,30,32and two thrust pistons34,36(or jacks) for locking the support assembly22in operative position with respect to the surface to be machined. The pistons34,36are preferably linked with each other by a transverse member44for rigidity purposes. The pistons34,36can be operated using the gas supply in the umbilical cable10(shown inFIG. 1). With appropriate gas pressure, both pistons34,36extend so that their feet46,48press against the surface6′ opposite to the surface6to be machined. As a result, the pistons34,36cause a counteraction on the levelling legs28,30,32, so that the robot2is held in position by friction inside the slot4(shown inFIG. 2) with five pressure points. A camera support50can be secured to the transverse member44in order to support and direct a camera53for viewing the displacement of the mobile members24,26.

The robot2has a watertight enclosure52containing electric and electronic components forming an onboard control unit128(shown inFIG. 7). The enclosure52is connectable to the umbilical cable16(shown inFIG. 1) and to other sensor and actuator cables (not shown) of the robot2. The cables going toward the mobile members24,26preferably pass through flexible cable guides54,56that protect the cables and allow fluid movement of the mobile members24,26. The onboard control unit128is programmable and allows operating the motors58,60and possibly a motor62for operating the tool92(shown e.g. inFIG. 4). The control unit128may 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.

The robot2may be provided with a pump64preferably extending outside the slot4(shown inFIG. 2) and attached to the enclosure52for example by a tightening clamp66. The pump64is connectable to a suction nozzle68(shown inFIG. 5B) on the tool holder42through a flexible hose or pipe70, 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 pump64or discharged at the surface for subsequent processing.

The robot2may be fastened to the cable12(shown inFIG. 1) using one of the fastening arrangements20,20′ provided at the opposite ends of the support assembly22, depending on the surface6,6′ of the slot4(shown inFIG. 2) to be machined. In the illustrated case ofFIG. 2, the fastening arrangement20is used for milling the surface6. The fastening arrangement20′ would then be used for milling the surface6′.

The robot2preferably 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.

Referring toFIG. 4, the mobile member24has two pairs of guiding shoes72(only one shoe72of a pair is apparent in the Figure, the other shoe of the same pair being hidden behind the motor58whereas the shoes of the other pair are respectively hidden by the tool holder42and the mobile member26) slideably mounted on the tracks38(shown inFIG. 3). The rack and pinion system used to move the mobile member24in the Y axis may be formed of a precision pinion74coupled to the motor58and engaging with a rack (not shown) extending on the support assembly22(shown inFIG. 3) in the Y direction. The motor58may be a hybrid stepping motor with an integrated reducer. Induction or other types of proximity sensors76may be mounted near ends of the guiding shoes72to detect the stops40(shown inFIG. 3) for limiting the displacement of the mobile member24.

Tracks78can be mounted on the member24for guiding the member26in the X axis in order to position the tool holder42with respect to the surface to be machined. A rack80in parallel with one of the tracks78can be used to move the member26.

Referring toFIGS. 5A and 5B, the member26has two pairs of guiding shoes82,84(better shown inFIG. 5B) slideably mounted on the tracks78(shown inFIG. 4). The rack and pinion system used to move the mobile member26in the X axis may be formed of a precision pinion88coupled to the motor60and engaging with the rack80(shown inFIG. 4). The motor60may be a hybrid stepping motor with an integrated reducer.

Depending on the tool to be used by the robot2, the tool holder42may be provided with a tool bearing mechanism90to which the tool92can be secured in a possibly rotatable manner. The tool holder42may also be used to support an optional camera94, the suction nozzle68coupled to the flexible pipe70(shown inFIG. 3), and a sensor96. The camera94may be used to view the working area of the tool92. The sensor96may be positioned close to the tool92and arranged to perform a relative distance measurement between a reference point of the robot2and a corresponding point on the surface to be machined. The sensor96may 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.

The tool92may be driven in rotation by a sprocket wheel98driven by another sprocket wheel100through a sprocket belt102(better shown inFIG. 5B) whose tension is controlled by a tightener104. The tool bearing mechanism90then rotatably supports the tool92and transmits rotation of the sprocket wheel98to the tool92. The wheel100may be coupled to the motor62through a magnetic coupling clutch mechanism106for transmitting rotation of the motor62to the sprocket wheel100. Other types of coupling mechanisms may be used if desired, and a direct drive configuration may also be used to drive the tool92to simplify the driving arrangement if desired, for example depending on the size and power of the motor62.

Referring toFIG. 6, there is shown a possible construction for the levelling legs28,30,32. A levelling foot108slideably projects under a housing110. The foot108is connected to a linear actuator made of an ACME screw assembly having a shaft112with a longitudinal keyway coupled to a rotatable nut114. The nut114forms a toothed pulley coupled to a driving toothed pulley118through a belt116provided with a tightener122. The driving pulley118is driven by a motor120, e.g. a hybrid stepping motor with integrated reducer. Lowering and raising of the foot108is achieved by operating the motor120in one direction or the other so that rotation of the driving pulley118is transmitted to the pulley-like nut114by the belt116, and rotation of the nut114is converted into a linear motion of the shaft112to which the foot108is connected. A proximity sensor124e.g. of an inductive type may be mounted on the housing110to detect a metal hook126projecting at an upper end of the shaft112in order to limit a farthest course of the foot108under the housing110.

Referring back toFIG. 3, the foregoing construction of the robot2allows it to be used in a water depth of at least 30 meters. The mechanical structure of the members24,26and 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 assembly22is adapted to the efforts to which it is subjected to. The positioning capacities of the robot2, 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.

The five degrees of freedom of the robot2allows, with respect to the tool92(shown inFIG. 4), a X axis translation resulting from the displacement of the mobile member26, a Y axis translation resulting from the displacement of the mobile member24, and a Z axis translation (perpendicular to the X-Y plane) resulting from the combined displacement of the three levelling legs28,30,32and two rotations (one around the X axis, another one around the Y axis) resulting from the displacement of one or two levelling legs28,30,32while the third one remains fixed.

For a precise positioning of the robot2for 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 robot2with respect to a reference point such as a point located in an upper portion of the slot4(shown inFIG. 1) out of the water. The method uses a starting reference point and local references between every displacements of the robot2in order to find a relative position with respect to a previous position to determine a current position of the robot2by computations.

Referring toFIG. 1, the positioning method may proceed as follows.

1. From the surface, using the cable12, the robot2is vertically positioned in the slot4in front of the first section to be machined, engageable through the slot opening. A lower portion of the robot2may be submerged while an upper portion of the robot2remains out of the water.

2. Pneumatic pressure is turned on to actuate the pistons34,36in order to lock the robot2in the slot4.

3. Two mirror references located on the upper portion of the robot2are 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 legs28,30,32(shown inFIG. 3), the orientation (rotation) of the X and Y axes of the robot2is adjusted until the X-Y plane required for the restoration is reached. The robot2is then initialized at its zero machine point.

4. The machining operation is performed on the current machining area using X, Y and Z translation movements as provided by the robot2. A trajectory algorithm may be used to compensate small deviations in rotation in the Z axis that may occur (Arz). Optionally, the sensor96(shown inFIG. 4) may carry out a complete or partial scan of the surface before and/or after the machining operation.

5. The pneumatic pressure is turned off to release the pistons34,36to allow vertical movements of the robot2in the slot4.

6. The robot2is lowered in the slot4about 90% of its effective machining vertical range (for a 1 m range, the robot2would be lowered about 900 mm). In other words, the robot2is 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 slot4). If the bottom of the slot4is reached, this will be the last machined section.

7. The pneumatic pressure is turned on to actuate the pistons34,36to lock the robot2in the slot4for the new machining task.

8. The 10% overlapping surface restored during the last machining operation is measured with the sensor96(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 robot2may be correctly obtained as a function of the precision of the measurements carried out. Optionally, other sensors like inclinometers (not shown) on the robot2may be coupled to the algorithms to reduce possible detection errors.

9. The orientation (rotation) of the X and Y axes of the robot2is 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.

10. Return to step 4.

Other 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.

Referring toFIG. 7, there is shown a schematic simplified control diagram of the robot2. The onboard control unit128in the watertight enclosure52controls motor drives130connected to the motors60,58,28,30,32and62. The onboard control unit128communicates with the measurement sensor unit96to receive the distance data computed by the sensor. The onboard control unit128also receives proximity alert signals from the proximity sensors76,77and124, 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 station18has a user interface monitor132, a user interface computer134, an electronics power supply unit136and a motors power supply unit138. The umbilical cable16connects the control station18with the watertight enclosure52. The electronics power supply unit136provides the supply to the onboard control unit128, the proximity sensors76,77,124, the measurement sensor unit96and possibly the cameras53,94through the umbilical cable16. The video signals from the cameras53,94can be transmitted through the umbilical cable16to the user interface computer134or to a separate monitoring unit (not shown) if desired. The motors power supply unit138provides the supply to the motor drives130through the umbilical cable16. The user interface computer134has a bidirectional communication link with the onboard control unit128also through the cable16. A video signal from the user interface computer134is sent to the user interface monitor132.

While 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 assembly22, the mobile members24,26, the tool bearing mechanism90, the magnetic coupling mechanism106and the housing110may be constructed differently, as long as their constructions are submersible, have rigidities resisting to the direct and indirect efforts produced by the tool92, and fulfill functions similar to those described above. The motors120of the legs28,30,32, the motors58,60for moving the mobile members24,26, and the thrust pistons34,36contribute to the precision of the displacements of the tool92and provide an appropriate displacement and positioning range for the tool92with respect to the target surface for a machining task or another similar task. The motors120,58,60may be of different types and constructions if desired, as long as they allow the required positioning of the mobile elements24,26,28,30,32. The motors120,58,60can 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 sensors76,124may be positioned otherwise and be of other types if desired.

It is possible to use the robot2in 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 cable12providing from the hoisting system at the surface. The locking arrangement of the robot2in the slot4with 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.

The robot2may 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.