US 20040099175 A1
The train (1) of modules (2 to 6) that forms the robot comprises springs (38) to connect the successive modules together enabling curvature of the train in the bends of a pipe. However, cables (41) bring the modules together by compressing the springs when they are pulled, until the conical end faces (39, 40) are engaged in each other; the train is made rigid and can be immobilised inside the pipe to perform different types of machining operations, including welding or cutting joints between successive pipes in the pipework.
1. Robot free to slide inside pipework or another narrow passage, composed of a train of modules (2 to 6, 10) connected by flexible links (38), characterised in that it comprises means of fixing (41) modules to each other to stiffen the train.
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 This application claims priority based on International Patent Application No. PCT/FR01/02324, entitled “Mobile Robot That Can Operate In Pipes Or Other Narrow Passages” by Yann Perrot, Olivier David and Jean Lehu, which claims priority of French application no. 00/09387, filed on Jul. 18, 2000, and which was not published in English.”
 The domain of the invention is mobile robots for work, inspection or generally displacement inside pipework or other narrow passages.
 Robots composed of a small vehicle or an inert module pushed from behind are known, for penetration into pipes and to carry out specific work or inspections in pipes. However, it may be difficult when these robots have to go round bends in the pipework, since they cannot be very long otherwise they would get jammed. One possible solution is to construct a robot consisting of a train of modules formed to be flexible, but it then becomes difficult to stop and hold the robot at a specific place in the pipework and even more difficult to fix it such that it remains immobile despite large forces that it may transmit to the pipework, and despite large reaction forces that may be applied to it during specific work such as machining of the inside of the pipework.
 The invention offers a solution to this problem; it relates to a robot free to move by sliding in pipework or in another narrow passage, composed of a train of modules connected by flexible links and characterised in that it comprises means of fixing the modules together.
 Thus, the robot is flexible so that it can go around bends in pipes, but becomes rigid when required and is then capable of being fixed firmly in the pipework and supplying good resistance. Above all, the inhibition of flexible links stiffens the train to resist bending.
 Some favourable implementations of the invention make it possible to hold the robot at a chosen location in the pipework, by controlling appropriate mechanisms. It then becomes possible and beneficial to provide the robot with manual release mechanisms so that retraction of the holding mechanisms can be controlled manually so that the robot can be made free to move again even if direct control of the holding mechanism motors fail.
 A particular operation consists of assembling segments of pipework put end to end in sequence; the robot according to the invention can do this operation if it is built such that two portions of an anterior module can be brought towards each other, one of these portions being held in place on the free segment and the other being fixed to the previously assembled length of the pipework.
 Other important elements of the invention, and particularly specific means of performing the functions described above, will be described in detail with reference to the following figures:
FIG. 1 is an overview of the robot,
FIG. 2 is a view of a propulsion module,
FIG. 3 is a view of a holding module,
FIG. 4 shows the train stiffening system,
FIG. 5 is a view of an anterior module,
FIG. 6 illustrates the anterior module immobilised in the pipework,
FIG. 7 illustrates the forced release mechanism of the anterior module,
FIG. 8 shows another holding means for a module,
FIG. 9 illustrates a train composed of such modules,
FIG. 10 illustrates a case in which the invention is used,
FIGS. 11A and 11B show a module carrying a machining tool.
 The embodiment of the invention as shown in FIG. 1 in a pipe bend comprises five modules numbered from 2 to 6 from the head to the tail; the head or anterior module is an alignment module 2 that the robot 1 uses to form a path in the pipework; the next module is a tool module 3 carrying a working tool; the next module is a power module 4 supplying energy to the previous module; the fourth module is an auxiliary functions module 5; the tail or posterior module in this embodiment is an immobilisation module 6. Neither the number nor the function of the modules characterise the robot according to the invention or restricts its scope, since it is obvious that the invention could be implemented with different robots. In particular, a propulsion module that will be described a little later could be added at the tail. In this embodiment, it would be superfluous because robot 1 is designed to be pushed inside the pipework by means of a flexible rod 7 attached to the rear of the tail module through crimping 8. The rod 7 is flexible at bends in the pipe, but it transmits all longitudinal forces imposed on it and therefore pushes the robot 1 forwards. It tends to deform at the largest possible angle of curvature in a bend, separating from the extrados as shown in the diagram in the right part of FIG. 1, at location 9. Therefore, it is fairly easy to calculate the penetration of the robot 1 as a function of the length of the rod that has penetrated into the pipework.
FIG. 2 shows a standalone propulsion module 10. Its enclosure 11 contains a motor 12 on which the shaft 13 is a screw driving three toothed wheels 14. Each of them drives a pulley 15 that is coaxial with it, and another pulley 17 fixed to a roller 18 through a belt 16. The rollers 18 are distributed at 120° around a rear circumference of the enclosure 11 and are placed at the end of levers 19 hinged about an axis 20 at their opposite end and mutually separated by springs 21, so as to withdraw rollers 18 away from the enclosure 11 until they are pressed into contact on the wall of the pipework. Another similar expandable roller system, globally referenced 22, is placed in front of the propulsion module 10, except that these rollers are not driving and therefore they simply complement centring of the module 10 in the pipework. A double universal joint 23 connects the module 10 to the back of the immobilisation module 6 so that a radial alignment fault can be accepted between them. Since the motor 12 is fairly long and thin, the enclosure 11 has a recessed shape at the centre so that it can pass through the tightest bends despite its length.
 At least two modules have an immobilisation or holding system in the pipework that will be described below; one of them is the immobilisation module 6 fully illustrated in FIG. 3; its enclosure 25 is perforated by three concentric holes through which diverging pins 26 can pass, and finishing at the pipework on a bearing surface 27. The enclosure 25 surrounds three motors 28 fixed to a common support plate 29 and that rotate the screws 30 designed to move the threaded cams 31 forwards, the surfaces 32 of which push on the back faces 33 of the pins 26. The cam surfaces 32 are not simple wedge surfaces, but comprise at least two slopes, the first 34 being steeper so that the pins 26 can be pushed more quickly while the other surface 35 is shallower and adjusts the pressure force of the pins 26 on the pipework. The rotations of motors 28 are synchronised using a belt 36 tensioned in a triangular arrangement around three gears 37 at the ends of the screws 30 at the other end of the motors 28. As a variant, it would be possible to have a single motor to control the three screws 30 at the same time, using separate transmission means.
 We will now describe an essential aspect of the invention with reference to this FIG. 3, and FIG. 4; they are means of physical and electrical connections of modules 2 to 6 in the train that comprise helical springs 38 fixed between two consecutive modules, and an outside conical male face 39 on the enclosure of each module at the back and an internal female conical face 40 at the front. The only exception is the alignment module 2, which is specially shaped at the front so that the robot 1 can easily form its path. The springs 38 are associated with stiffening cables 41 that pass through all modules 2 to 6 and extend as far as the alignment module 2, behind which they are connected. In fact, there are three stiffening cables 41 distributed uniformly around the circumference for a balanced transmission of the force. The stiffening cables 41 slide in ducts 42 behind the immobilisation module 6, extending as far as a tension mechanism 43 comprising a distribution plate 44 to which the stripped ends of the stiffening cables 41 are attached, a screw 45 at the end of which the distribution plate 44 is fixed, a nut 46 fitted on the screw 45 and a motor 47 making the nut 46 turn driven by a pulley and belt transmission 48; the screw 45 slides pulling the distribution plate 44 with it so as to pull the alignment module 2 backwards. But if the immobilisation module 6 is held on the pipe by the expanded pins 26, it will remain immobile, the other modules 2 to 5 will move closer to it and the train will contract, until the male conical surfaces 39 penetrate into the female conical surfaces 40 such that the consecutive modules 2 to 6 join together forming a single compact high strength robot element, particularly incapable of bending. When the stiffening cables 41 are released, the springs 38 can relax and the train then becomes flexible once again. In a variant not shown, a cable tensioning device is installed onboard.
 We will now describe FIG. 5 and the alignment module 2 of the robot 1 in the pipework. It comprises a conical head 50 at the front connected to a main body 51 through a bellows 52 and containing a motor 53, the shaft 54 of which rotates a ball screw 55 housed in the main body 51 through a double universal joint 56 that surrounds the bellows 52. A nut 49 driven by the ball screw 55 on the centre line of the ball screw drives a complex shaped cam 57 that occupies most of the main body 51. It comprises main oblique tracks 58 to control the expansion of the clamping pins 59 similar to the pins (26) described for the immobilisation module 6, secondary oblique tracks 60 to control the expansion of connection pins 61 to the next module 3, and a shoulder 62 at the back to control the backwards displacement of an enclosure skin 63 carrying pins 59 along the main body 51. This displacement is directed against springs 64 fixed to a main enclosure 65 of the main body 51 and that push the enclosure skin 63 forwards; as a reminder, note the other springs 66 and 67 that pull pins 59 and 61 towards the inside of the main body 51 and a spring 68 that pulls the cam 57 forwards. The advantage of this innovative assembly can easily be understood with reference to FIG. 6; the pins 59 expand and enter into a groove R around the edge of a forward portion A of the pipework. This groove R marks the progress of robot 1 in the pipework, indicating a stop position at which work can be done. However, the front portion A is not necessarily joined to the rear portion B of the pipework if the work to be done is to weld the joint J between them.
 Therefore, the first effect of a displacement of the cam 57 is to immobilise the main body 5 of the alignment module 2 in the forward portion A of the pipework and on the tool module 3 by extending the pins 59 and 61; the shoulder stop 62 on the enclosure skin 63 then pushes the enclosure skin, the pins 59 and finally the front portion A until it touches the rear portion B. The joint J is then formed in front of the tool module 3 that can begin to work. The robot 1 can thus be used to assemble a complete line of pipes from the inside. The bellows 52 and the ball joint 56 are sufficiently flexible so that the conical head 50 can be engaged in the badly positioned forward pipework A, that can then be straightened by the cam 57 mechanism.
 In other applications, the pins 59 are only used to immobilise the train of modules 2 to 6 inside the pipework, and the module 3 tool may be a grinding wheel or a knife or a sensor to perform various types of inspections or machining on the joint J, or to cut it; the alignment module 2 then holds the forward portion of the pipework A on the other side of the cut; normally, there is no need to worry about a misalignment in the pipework due to internal stresses at the cut at joint J, since the stiffness of the assembly of the train of modules 3 and their fixity is not sufficient to prevent all deformation of the robot 1.
 Another aspect of the invention, also present on the alignment module 2, will now be described with reference to FIG. 7. This aspect relates to the need to control loosening of pins 59 and 61 even if there is a failure in the control motor 53 of the cam 57, or for any other reason. A manual command using a cable 70 parallel to the stiffening cables 41 is then provided, this cable projecting backwards from the pipework like the stiffening cables. The end of the cable 70 is wound in a loop 71 around a safety ring 72 that holds a mobile ring 77 in place close to a shoulder 73 at the end of the main body 51, despite the action of springs 78 compressed between the shoulder 73 and the mobile ring 77.
 However, a fairly strong tension on the cable 70 is sufficient to tear the safety ring 72 out of the groove of the main body 51 that held it in place, which releases the mobile ring 77 that the springs 78 push backwards. It releases a pin 75 that fixes a fixed ring 74 attached to the ball screw in rotation to the output shaft from universal joint 56; a spring 76 ejects the pin 75 and breaks the connection between the ball screw 55 of the motor 53; the spring 68 can then expand and push the cam 57 forwards due to the reversibility of the transmission between the ball screw 55 and the nut 56; and the springs 66 and 67 make the pins 59 and 61 retract.
 A similar device is provided for the other tightening pins. Returning to FIG. 3, it can be seen that there is one for the immobilisation module 6; a cable 78 similar to cable 70 terminates in a loop 79 around a safety ring 80 so that the safety ring is torn off when it is pulled, which releases the support plate 29 carrying the motors 28 from a nose 81 fixed to the enclosure 25 of the module. Springs 83, previously compressed between the carrier plate 29 and the distribution plates 84 fixed to the enclosure 25, then expand to push the support plate 29 backwards so as to make the cams 31 withdraw. The relaxation of springs 82 placed between the enclosure 25 and the pins 26 retracts the pins and releases the robot.
FIGS. 8 and 9 show that other immobilisation means for the modules could be used, and particularly shape memory pads 85 that can be in the form of discontinuous hoops around the different modules. A shape memory alloy part has the special feature that it can take on two different shapes by changing its metallurgical structure at a transition temperature, and return to the shape that was imposed on it when its temperature increases to above the transition temperature in a preliminary manufacturing step. In this case, the pads 85 tend to straighten above the transition temperature, and their ends are trapped in contact with the inside face of the pipework. At the same time, their ends remain in the grooves 86 in the modules, which holds them firmly in place. Electrical power supplies, not shown, increase the temperature of the pads 85. This system has the advantage that cutting off the electrical current necessarily brings the pads 85 back to their initial shape and releases the module train, and the release cable systems described with reference to FIG. 7 become unnecessary. However, FIG. 9 suggests that it is useful to hold the immobilisation pins 59 of the alignment module 2 that are also useful as positioning references in the groove R of the pipework for all tasks in which the robot has to be stopped at a specific location.
 Obviously, all types of tools can be used; the robot was developed specifically to be capable of performing processes that involve five operations on the pipework, namely cutting, knurling, spot welding, welding and ultrasound inspection. Five similar module trains can advantageously be used, in which the tool module 3 is different in each train. As can be seen in FIG. 10, the trains 1 a to 1 e may be suspended in a circle from a drum 86 by independent advance mechanisms 87 lowered in sequence into the line of pipework to be treated after rotation of the drum 86 that rotates on a base 88. For example, it would be possible to treat several lines in nuclear power station steam generators that comprise a large number of parallel pipework lines to be treated, with a phase offset for each line, and pushing several module trains into different lines simultaneously.
FIGS. 11A and 11B show that the tool modules 3 usually include two motors 91 and 92 on each side of a tool 93 (in this case a cutter that could be replaced by a circular grinding wheel); the first of these motors rotates the tool 93 around its axis through a universal joint 94, and the second makes a cylindrical casing 95 rotate outside a slit 96 from which the tool 93 projects, about its axis by a gear 97. The tool 93 is at the end of a lever 98 that pivots about an eccentric axis 99 in the casing 95 and that is pushed by a linkage mechanism 100 with screw control 101 activated by a third motor 102 and a connecting gear 103, and a rocker arm 104, the opposite ends of which are articulated to the lever 98 and to a gland 105 engaged in the screw 101; furthermore, the screw 101 reaches the shaft 99. Therefore, movements of the motor change the distance between the gland 105 and the shaft 99 and the angle of the lever 98 and the rocker arm 104, which makes the rocker arm rotate and extend and retract tool 93 before and after its work on a pipework joint.
 Circular joints can be machined by a combination of the rotation movement of the tool 93, the exit movement of the tool 93 and the rotation movement of the casing 95. We will not discuss these machines for machining inside a pipework any further, some of which have already been designed, but we will simply mention once again that the casing 95 extends between two half-enclosures 106 and 107 of the tool module 3, which come closer to each other when the springs 38 are compressed until they come into contact with the casing 95 while allowing the casing to rotate. Complementary springs 108 separate the two half-enclosures 106 and 107 when the springs 38 are released.