FR3104231A1 - MOBILE ROBOTIC DEVICE WITH ARCHIMEDAL SCREW PROPULSION ASSEMBLIES TO INSPECT PIPES OF DIFFERENT DIAMETERS - Google Patents

Abstract

The invention lies in the field of mobile robots moved by at least one pair of Archimedes screws. It relates to a mobile robotic device (1) comprising: a main body (10), a first propulsion assembly (20A) and a second propulsion assembly (20B) arranged on either side of the main body and each comprising: a side body arranged to receive a propulsion motor, a drum (22A, 22B) mounted in pivot connection with respect to the side body along an axis of rotation and arranged to be driven in rotation by the propulsion motor, and a screw thread d Archimedes (23A, 23B) secured to the drum and projecting from an outer surface of the drum. According to the invention, the mobile robotic device (1) further comprises an adjustable structure (30) arranged to fix the side body of each propulsion assembly (20A, 20B) to the main body (10) and to be able to modify a position of at least one propulsion assembly (20A, 20B) relative to the main body so as to modify a distance between the axes of rotation of the propulsion assemblies. Figure for abstract: Figure 2B

Description

MOBILE ROBOTIC DEVICE WITH ARCHIMEDES SCREW PROPULSION SETS TO INSPECT PIPELINES OF DIFFERENT DIAMETERS

The invention lies in the field of mobile robots and, more specifically, in the field of robots moved by at least one pair of Archimedes' screws. It relates to such a mobile robotic device comprising a main body and at least two propulsion assemblies arranged on either side of the main body, each propulsion assembly comprising an Archimedean screw, so as to allow movement of the robotic device as well on a rigid support than on a loose or liquid support.

The invention applies in particular to the inspection of pipes, for example industrial, rainwater or waste water pipes. More generally, the invention finds an application for any deployment of a mobile robotic device on difficult terrain, for example soft, wet and/or granular.

The inspection of the interior of pipes in urban or industrial networks can be carried out by mobile mechatronic devices comprising image sensors and/or sensors for measuring various physical and/or chemical parameters. When the locomotion function of such devices is ensured by wheels or even tracks, these devices may find themselves blocked in their progress by the presence of obstacles in the bottom of the pipe, such as water, grease, sand or mud. In order to avoid such blockages, it is sometimes possible to scour the pipe to be inspected before passing the device. However, the scouring operation has drawbacks in terms of speed of intervention, complexity and cost.

In order to allow a progression of a mobile robotic device on a difficult terrain, one possibility is to equip it with one or more Archimedean screw propulsion sets. The Archimedes screw thread comes into contact with the ground and allows progression regardless of the type of surface encountered, the screw thread penetrating the ground to a greater or lesser extent. Application WO2016/177436A1 describes such an example of a robotic device suitable for inspecting a pipe. The robotic device includes one or two pairs of propulsion assemblies arranged on either side of a body. Each propulsion assembly comprises a drum whose exterior surface has an Archimedean screw thread and an electric motor housed in the body in order to rotate the drum relative to the body. The robotic device can thus evolve on most types of surfaces likely to be encountered on the bottom of a pipe. However, when the robotic device evolves on a loose, muddy or granular support and the Archimedean screw threads sink into this support, the friction surface between the drum and the support becomes relatively large. A large amount of energy is then expended to move the robotic device forward. Since the robotic device is powered by an on-board energy storage source, its autonomy is then limited. In an alternative embodiment of the robotic device described in application WO2016/177436A1, wheels are integrated into the Archimedean screw threads in order to limit friction between the drums and the support on which the robotic device moves. However, the wheels have a narrow tread and are ineffective on loose ground. Application WO2018/065710 A1 describes an embodiment of an Archimedean screw robotic device in which wheels having a wide tread are used. However, the contact surface between the wheels and the loose support may be insufficient to prevent the wheels from sinking into the support. A further increase in tread width is possible but leads to increased friction on a rigid support. A compromise must then be found so that the wheels are adapted to the different types of surfaces encountered in the bottom of a pipe.

In addition, significant obstacles can obstruct the bottom of a pipeline, which complicates or even makes impossible the progression of the robotic device, including when it is equipped with Archimedean screw propulsion assemblies.

Consequently, the mobile robotic devices of the state of the art do not give complete satisfaction when they are used in a pipe whose bottom is cluttered with mud and with obstacles varying along this pipe. The invention thus aims to provide a robotic device capable of progressing along a pipe regardless of the nature of the support present on the bottom. Another object of the invention is to provide a robotic device whose design, manufacturing and maintenance costs are compatible with use on an industrial scale.

To this end, the invention proposes a mobile robotic device comprising at least one pair of propulsion assemblies arranged on either side of a main body, each propulsion assembly comprising an Archimedean screw in rotation relative to the main body along an axis of rotation. The robotic device is arranged so that a distance between the axes of rotation is adjustable in order to adapt the robotic device to the diameter of the pipe. In particular, the distance between the axes of rotation can be adjusted so that the Archimedes' screws bear against the wall of the pipe above any sludge present in the bottom of the pipe. The Archimedes screws thus remain in contact with the same type of surface throughout the progress of the robotic device in the pipe.

Another advantage of the possibility that the robotic device according to the invention alternatively has a relatively large or relatively small distance between the axes of rotation of the propulsion assemblies is to confer both great stability on the robotic device during its evolutions, and a limited footprint when not in use.

More specifically, the subject of the invention is a mobile robotic device comprising:

a main body,

a first propulsion assembly and a second propulsion assembly arranged on either side of the main body, each propulsion assembly comprising:

a side body arranged to receive a propulsion motor,

a drum mounted in pivot connection relative to the side body along an axis of rotation and arranged to be driven in rotation by the propulsion motor, and

an Archimedean screw thread secured to the drum and projecting from an outer surface of the drum.

According to the invention, the robotic device further comprises an adjustable structure arranged to fix the side body of each propulsion assembly to the main body, the adjustable structure being arranged to be able to modify a position of at least one propulsion assembly by relative to the main body so as to modify a distance between the axes of rotation of the propulsion assemblies.

Each drum extends longitudinally along its axis of rotation and forms an envelope covering all or part of the side body with which it is pivotally connected. Preferably, the drum covers at least 80% of the side body, in order to maximize the surface of the mobile parts of the robotic device with respect to the surface of the fixed parts.

According to a particular embodiment, the adjustable structure comprises a first arm fixed to the side body of the first propulsion assembly and arranged to be able to slide relative to the main body. A distance between the axis of rotation of the first propulsion assembly and the main body, and therefore the distance between the axes of rotation of the two propulsion assemblies can thus be modified.

Advantageously, the adjustable structure further comprises a second arm fixed to the side body of the second propulsion assembly and arranged to be able to slide relative to the main body. The possibility of causing each arm to slide relative to the main body makes it possible to maintain symmetry of the robotic device relative to a median plane, parallel to the axes of rotation of the propulsion assemblies.

According to a particular embodiment, the first arm is arranged to be able to slide relative to the main body along a first axis of translation and the second arm is arranged to be able to slide relative to the main body along a second axis of translation. According to another particular embodiment, each arm is arranged to be able to slide along a curve, for example an arc of a circle.

The first axis of translation and the second axis of translation can form an angle comprised between 90 degrees and 180 degrees. This angle is for example formed in a transverse plane of the robotic device, orthogonal to the axes of rotation of the propulsion assemblies. Preferably, the angle is between 110 degrees and 160 degrees. The arms can then form an inverted V making it possible to leave a free space under the main body and the arms around the mid-plane of the robotic device.

The adjustable structure may include at least one guide pin for each arm, each guide pin being integral with the main body. Each arm can then include a guide groove arranged to accommodate said at least one respective guide pin. The sliding of each arm relative to the main body is thus ensured by guiding the guide pin or pins in the guide groove of this arm. In the presence of two arms, a guide pin may be common to the guide grooves of the two arms. When the arms slide along a first and a second translation axis, each guide groove extends along this respective translation axis.

The adjustable structure may further comprise a locking mechanism arranged to take alternately a locked configuration, in which it prevents the sliding of each arm relative to the main body, and an unlocked configuration, in which it allows the sliding of each arm relative to the main body.

The locking mechanism may comprise any type of quick-locking means, for example a screw or a quick-tightening lever.

According to a first particular embodiment, the locking mechanism comprises for example a screw arranged to pass through the guide groove of each arm and to be inserted into the main body. The screw is arranged, in the locked configuration, to press each arm against the main body and, in the unlocked configuration, to leave functional play between each arm and the main body. In the unlocked configuration, the screw can itself play the role of the guide pin common to the two arms.

According to a second particular embodiment, the locking mechanism comprises at least two positioning holes formed on each arm, and a screw arranged to pass through one of the at least two positioning holes and to be inserted into the main body. Each positioning hole defines a respective position of the arm relative to the main body. Each positioning hole or, in the presence of two arms, each pair of positioning holes, can thus be associated with a predetermined distance between the axes of rotation of the propulsion assemblies.

According to a particular embodiment, the robotic device further comprises a drive mechanism arranged to modify the position of the at least one propulsion assembly relative to the main body. The position of this propulsion assembly or these propulsion assemblies is then no longer modified manually but by an automatic mechanism. The distance between the axes of rotation of the propulsion assemblies can thus be modified remotely, in particular during the evolution of the robotic device in a pipeline.

When the adjustable structure comprises at least one arm sliding relative to the main body, the drive mechanism may comprise an adjustment motor and, for each arm, a rack and a toothed wheel. Each rack is integral with a respective arm and extends parallel to a sliding curve of this arm relative to the main body. Each toothed wheel is in pivot connection with the main body and meshes with the rack of a respective arm. The adjustment motor is arranged to drive the toothed wheel(s) in rotation. Thus, during rotation of the adjustment motor, each toothed wheel is driven in rotation and generates sliding of the arm integral with the rack associated with said toothed wheel.

When the adjustable structure has a second arm, the toothed wheels can mesh with each other, the adjustment motor being coupled to one of the toothed wheels. A single adjustment motor is then necessary.

According to a particular embodiment, the robotic device may comprise a third propulsion assembly and a fourth propulsion assembly, each propulsion assembly comprising:

a side body arranged to receive a propulsion motor,

a drum mounted in pivot connection relative to the side body along an axis of rotation and arranged to be driven in rotation by the propulsion motor, and

an Archimedean screw thread secured to the drum and projecting from an outer surface of the drum.

The side body of the third power set can be fixed to the side body of the first power set and the side body of the fourth power set can be fixed to the side body of the second power set.

Advantageously, the robotic device has symmetry with respect to a transverse plane. In particular, the axis of rotation of the third propulsion assembly may coincide with the axis of rotation of the first propulsion assembly and the axis of rotation of the fourth propulsion assembly may coincide with the axis of rotation of the second assembly propulsion.

According to a particular embodiment, the Archimedes screw threads of the first and fourth propulsion sets are right-hand threads and the Archimedes screw threads of the second and third propulsion sets are left-hand threads. Consequently, the propulsion assemblies of the same axis of rotation have threads that are inverted relative to each other, which allows greater maneuverability of the robotic device.

According to a particular embodiment, each propulsion assembly further comprises rolling members mounted in a pivot connection on the corresponding drum and distributed along the Archimedean screw thread so as to be driven in rotation by contact with the ground as the drum rotates. The running gear makes it possible to limit the friction between the drums and the support on which the robotic device moves. Running gear is particularly useful on a hard support such as a metal wall or a concrete wall of a pipeline.

A running gear tread may form a portion of an Archimedean screw thread or be located close to this screw thread. Advantageously, each running gear protrudes relative to the Archimedean screw thread.

Other characteristics, details and advantages of the invention will become apparent on reading the following description, given solely by way of example and made with reference to the appended drawings for which:

represents, in a partially exploded perspective view, an example of a mobile robotic device according to the invention;

shows in more detail, in a view analogous to FIG. 1A, an adjustable structure of the robotic device of FIG. 1A;

shows, in a perspective view, the robotic device of Figure 1A in a collapsed configuration;

shows, in a perspective view, the robotic device of Figure 1A in a deployed configuration;

shows, in a front view, the robotic device of Figure 2A in a pipe of relatively small diameter;

shows, in a front view, the robotic device of FIG. 2B in a pipe of relatively large diameter;

represents another example of a segment capable of forming an arm of the robotic device according to the invention;

represents yet another example of a segment capable of forming an arm of the robotic device according to the invention;

shows, in a partial perspective view, another example of a mobile robotic device according to the invention in a folded configuration;

shows, in a view analogous to FIG. 5A, the mobile robotic device of FIG. 5A in a deployed configuration.

FIG. 1A represents, in a partially exploded perspective view, an example of a mobile robotic device according to the invention. The robotic device 1 is particularly suitable for inspecting pipes. It comprises a main body 10, four propulsion assemblies 20A, 20B, 20C, 20D and an adjustable structure 30. Due to their analogy, the propulsion assemblies 20A, 20B, 20C, 20D are generally designated by the reference 20, c ie omitting the final letter of the individual references. Likewise, the various parts and parts of these propulsion assemblies are designated individually with a final letter A, B, C or D and generally without a final letter. By convention, the propulsion assemblies 20A and 20B define a front part and the propulsion assemblies 20C and 20D define a rear part. Propulsion assemblies 20A and 20C define a left portion and assemblies 20B and 20D define a right portion.

The main body 10 is shown detached from the other elements of the robotic device in FIG. 1. It is arranged to be fixed to the propulsion assemblies 20 by means of the adjustable structure 30. The body 10 comprises a housing 11 arranged to receive different electronic components. It can in particular accommodate a camera and lighting sources, not shown. The box 11 then comprises windows 12 facing the camera and the lighting sources. Preferably, the housing 11 is sealed.

Each propulsion assembly 20 comprises a side body 21, a drum 22, an Archimedean screw thread 23 and running gear 24. Each side body 21 generally has a tubular shape and is arranged to receive an electric propulsion motor and an electrical energy storage device such as a battery or an accumulator. Each drum 22 comprises a hollow cylinder of revolution 221, closed at a proximal end by a sealing ring 222 and closed at a distal end by a dome 223. The cylinders of revolution of the various drums 22A, 22B, 22C, 22D have a same outer diameter. Each drum 22 is mounted in a pivot connection relative to the respective side body 21 along an axis of rotation. The axes of rotation of the drums 22A and 22C coincide, as well as the axes of rotation of the drums 22B and 22D. Furthermore, the axis of rotation of the drums 22A and 22C is parallel to the axis of rotation of the drums 22B and 22D. The Archimedean screw thread 23 of each propulsion assembly 20 is integrally mounted on the outer surface of the corresponding drum 22. It spans both cylinder of revolution 221 and cupola 223. Archimedean screw threads 23A and 23D are right-hand threads and Archimedean screw threads 23B and 23C are left-hand threads . The rolling members 24 of each propulsion assembly are mounted on the corresponding drum 22 by being distributed along the Archimedean screw thread 23. Each rolling member 24 comprises a foot 241 integral with the drum 22 and a wheel 242 mounted in pivot connection relative to the foot 241. In the embodiment of Figure 1, the pivot connection of each wheel 242 is formed by an axle mounted at one end on the foot 241 and at another end on the screw thread d Archimedes 23. The rolling elements 24 are arranged so that a tread of their wheels 242 is locally parallel with the Archimedes screw thread 23.

FIG. 1B shows in more detail, in a view similar to FIG. 1A, the adjustable structure 30. The adjustable structure 30 comprises a first arm 31, a second arm 32, guide pins 33 and a locking screw 34. The first arm 31 is fixed to the side bodies 21 of the propulsion assemblies 20A and 20C and the second arm 32 is fixed to the side bodies 21 of the propulsion assemblies 20B and 20D. Each arm 31, 32 comprises a first segment 31A, 32A on the front side and a second segment 31B, 32B on the rear side, the segments of each arm surrounding the main body 10 on two of its opposite faces. Each segment 31A, 31B, 32A, 32B has a guide groove 311A, 311B, 321A, 321B, respectively, and two positioning holes 312A and 313A, 312B and 313B, 322A and 323A, 322B and 323B, respectively. Each positioning hole is formed at a guide groove and has a diameter greater than the width of the guide groove. The guide pins 33 are integral with the main body 10. A guide pin 33 on the front left side is housed in the groove 311A of the segment 31A and a guide pin on the rear left side is housed in the groove 311B of the segment 31B. Symmetrically, a guide pin 33 on the right front side is housed in the groove 321A of the segment 32A and a guide pin 33 on the right rear side is housed in the groove 321B of the segment 32B. The guide pins 33 have a diameter less than or equal to the width of the guide groove 311A, 311B, 321A, 321B, so as to allow them to slide in their respective guide groove. Elastic rings 35 are mounted on the guide pins in order to prevent the guide pins 33 from coming out of the grooves 311A, 311B, 321A, 321B. The grooves 311A, 311B extend perpendicular to the axes of rotation of the drums 22A, 22C along a first axis of translation and the grooves 321A, 321B extend perpendicular to the axes of rotation of the drums 22B, 22D along a second axis of translation. The first and second axes of translation form an angle of 140 degrees between them, so as to raise the main body 10 with respect to the propulsion assemblies 20. The locking screw 34 is arranged to pass successively through one of the positioning holes 312A , 313A of the segment 31A, one of the positioning holes 322A, 323A of the segment 32A, a through hole formed in the main body 10, one of the positioning holes 312B, 313B of the segment 31B and one of the positioning 322B, 323B of segment 32B. A nut, not visible in Figure 1, allows the screw 34 to be tightened. The locking screw 34 has a diameter greater than the width of the guide grooves 311A, 311B, 321A, 321B, so that when it is inserted in a positioning hole of a segment, it blocks the translation of this segment with respect to the main body 10. Each positioning hole therefore defines a relative position of the arms 31, 32 with respect to the main body 10, and therefore a relative position propulsion assemblies 20 with respect to the main body 10. In particular, the positioning holes 312A, 312B, 322A and 322B define a folded configuration of the robotic device, in which a distance between the axes of rotation of the propulsion assemblies 20A, 20C on the one hand, and 20B and 20D on the other hand, is relatively small, and the positioning holes 313A, 313B, 323A and 323B define a deployed configuration of the robotic device, in which the distance is relatively large. When the locking screw 34 is removed, the guide pins 33 can slide freely in the grooves 311A, 311B, 321A, 321B. The arms 31, 32 can then be positioned so that one of the positioning holes of each segment comes opposite the through hole arranged to receive the locking screw 34. The locking screw 34 can be tightened so as to press the segments 31A, 31B, 32A, 32B against the main body 10 and thus eliminate the operating games.

The robotic device 1 generally has symmetry with respect to a transverse plane passing through the main body 10 and symmetry with respect to a median plane, parallel to the axes of rotation of the propulsion assemblies 20.

Figures 2A and 2B show, in a perspective view, the robotic device 1 in the folded configuration and in the deployed configuration, respectively. The robotic device 1 can pass from one configuration to another simply by removing the screw 34, by sliding each of the arms 31, 32 via the guide pins 33 and the guide grooves 311A, 311B, 321A, 321B, and replacing the screw 34 in the positioning holes corresponding to the desired configuration.

Figures 3A and 3B represent, in a front view, the robotic device 1 inside a pipe. In FIG. 3A, the robotic device 1 is in the folded configuration in a pipe 2 having a diameter of 30 centimeters and in FIG. 3B, the robotic device 1 is in the deployed configuration in a pipe 3 having a diameter of 40 centimeters. It can be noticed that, both in the 30cm pipe 2 and in the 40cm pipe 3, the Archimedean screw threads 23 and the running gear 24 come into contact with the wall of the pipe at a height corresponding approximately one third of the diameter of this pipe. Consequently, the robotic device 1 is both able to be inserted into a pipe of relatively small diameter and to evolve in support on the wall of a pipe of larger diameter. Furthermore, the inverted V configuration allows the main body 10 and in particular the windows 12 to always be at substantially the same height in the pipe. Of course, the dimensions of the robotic device 1 and, in particular, of the arms 31, 32, can be adapted to different pipe dimensions.

Figures 4A and 4B show two other examples of segments capable of forming an arm of the adjustable structure. Segment 41A of Figure 4A has a guide groove 411A and five locating holes 412A into each of which locking screw 34 can be inserted. Each positioning hole 412A can be associated with a predetermined distance between the main body 10 and the corresponding propulsion assembly 20, that is to say a distance between the axes of rotation of the right and left propulsion assemblies. Segment 41B of Fig. 4B has a guide groove 411B and no locating hole. The locking screw 34 can then be positioned freely along the guide groove 411B.

Figures 5A and 5B show, in a partial perspective view, another example of a mobile robotic device according to the invention, in a folded configuration and in a deployed configuration, respectively. The robotic device 100 comprises a main body 10 and propulsion assemblies 20 identical to those of the robotic device 1 of FIG. 1. It further comprises an adjustable structure 40 comprising an arm 41 formed of segments 41A and 41B, and an formed of segments 42A, 42B. The segments 41A, 41B, 42A, 42B respectively include guide grooves 411A, 411B, 421A, 421B and differ in particular from the segments 31A, 31B, 32A, 32B in that they do not include positioning holes. The robotic device 100 further comprises a drive mechanism 50 arranged to actuate the adjustable structure 40, that is to say to modify the position of the propulsion assemblies 20 relative to the main body 10. The drive mechanism 50 comprises an adjustment motor, not shown, a first toothed wheel 51, a second toothed wheel 52, a first rack 53 and a second rack 54. The toothed wheel 51 is rotatably mounted around an axis of rotation orthogonal to the axis of translation of the arm 41 and the toothed wheel 52 is mounted in rotation around an axis of rotation orthogonal to the axis of translation of the arm 42 and parallel to the axis of rotation of the toothed wheel 51. The rack 53 is formed on a surface of segment 41B and the rack 54 is formed on a surface of segment 42B. The toothed wheel 51 meshes the toothed wheel 52 and the rack 53, and the toothed wheel 52 meshes the rack 54. The adjustment motor is for example an electric motor. It is housed in the main body 10 and is coupled to the toothed wheel 51, so as to be able to drive it in rotation. Thus, when the adjustment motor is actuated, it rotates the toothed wheel 51, which causes a rotation in the opposite direction of the toothed wheel 52. The rotation of the toothed wheels 51, 52 causes the movement of the arms 41, 42 along from their axis of translation towards the folded configuration, shown in FIG. 5A, or towards the deployed configuration, shown in FIG. 5B. The adjustment motor can have mechanical resistance when it is not actuated, allowing the arms 41, 42 to be held in position without tightening the locking screw 34. Said screw then only plays a role in guiding the arms 41, 42.

Claims (15)

Mobile robotic device (1, 100) comprising:
a main body (10),
a first propulsion assembly (20A) and a second propulsion assembly (20B) arranged on either side of the main body, each propulsion assembly (20A, 20B) comprising:
a side body arranged to receive a propulsion motor,

• a drum (22A, 22B) mounted in a pivot connection relative to the side body along an axis of rotation and arranged to be driven in rotation by the propulsion motor, and
• an Archimedean screw thread (23A, 23B) integral with the drum and projecting with respect to an outer surface of the drum,

the mobile robotic device (1, 100) being characterized in that it further comprises an adjustable structure (30, 40) arranged to fix the side body of each propulsion assembly (20A, 20B) to the main body (10 ), the adjustable structure (30, 40) being arranged to be able to modify a position of at least one propulsion assembly (20A, 20B) relative to the main body so as to modify a distance between the axes of rotation of the propulsion assemblies . Robotic device according to Claim 1, in which the adjustable structure (30, 40) comprises a first arm (31, 41) fixed to the side body of the first propulsion assembly (20A) and arranged to be able to slide with respect to the main body (10 ). Robotic device according to Claim 2, in which the adjustable structure (30, 40) comprises a second arm (32, 42) fixed to the side body of the second propulsion assembly (20B) and arranged to be able to slide with respect to the main body (10 ). Robotic device according to Claims 2 and 3, in which the first arm (31, 41) is arranged to be able to slide relative to the main body (10) along a first axis of translation and the second arm (32, 42) is arranged to able to slide relative to the main body (10) along a second axis of translation. Robotic device according to Claim 4, in which the first axis of translation and the second axis of translation form an angle comprised between 90 degrees and 180 degrees, preferably comprised between 110 degrees and 160 degrees. Robotic device according to one of Claims 2 to 5, in which the adjustable structure (30, 40) comprises at least one guide pin (33) for each arm (31, 32, 41, 42), each guide pin ( 33) being secured to the main body (10), each arm (31, 32, 41, 42) comprising a guide groove (311A, 311B, 321A, 321B, 411A, 411B, 421B) arranged to accommodate said at least one pin respective guide (33). Robotic device according to one of Claims 2 to 6, in which the adjustable structure (30, 40) further comprises a locking mechanism (34) arranged to alternately assume a locked configuration, in which it prevents the sliding of each arms (31, 32, 41, 42) relative to the main body (10), and an unlocked configuration, in which it allows the sliding of each arm relative to the main body. Robotic device according to Claims 6 and 7, in which the locking mechanism comprises a screw (34) arranged to pass through the guide groove (311A, 311B, 321A, 321B, 411A, 411B, 421B) of each arm (31, 32 , 41, 42) and fit into the main body (10), the screw (34) being arranged, in the locked configuration, to press each arm against the main body and, in the unlocked configuration, to leave functional play between each arm and the main body. A robotic device according to claims 6 and 7, wherein the locking mechanism has at least two positioning holes (312A, 312B, 313A, 313B, 322A, 322B, 323A, 323B) formed on each arm (31, 32), and a screw (34) arranged to pass through one of the at least two positioning holes and to be inserted into the main body (10). Robotic device according to one of the preceding claims, further comprising a drive mechanism (50) arranged to modify the position of the at least one propulsion assembly (20A, 20B) relative to the main body (10). Mobile robotic device according to Claim 10, taken together with one of Claims 2 to 9, in which the drive mechanism (50) comprises an adjustment motor and, for each arm (41, 42), a rack (53, 54) and a toothed wheel (51, 52), each rack (53, 54) being integral with a respective arm (41, 42) and extending parallel to a sliding curve of this arm relative to the main body ( 10), each toothed wheel (51, 52) being in pivot connection with the main body and meshing with the rack (53, 54) of a respective arm (41, 42), the adjustment motor being arranged to drive in rotation the toothed wheel(s) (51, 52). A robotic device according to claim 11 taken together with claim 3, wherein the gear wheels (51, 52) mesh with each other, the adjustment motor being coupled to one of the gear wheels. Robotic device according to one of the preceding claims further comprising a third propulsion assembly (20C) and a fourth propulsion assembly (20D), each propulsion assembly comprising:
a side body (21C, 21D) arranged to receive a propulsion motor,
a drum (22C, 22D) mounted in pivot connection with respect to the side body along an axis of rotation and arranged to be driven in rotation by the propulsion motor, and
an Archimedean screw thread (23C, 23D) integral with the drum and projecting with respect to an outer surface of the drum,
the side body (21C) of the third propulsion assembly (20C) being attached to the side body of the first propulsion assembly (20A) and the side body (21D) of the fourth propulsion assembly (20D) being attached to the side body of the second assembly propulsion (20B). A robotic device according to claim 13, wherein the Archimedean screw threads (23A, 23D) of the first and fourth propulsion assemblies (20A, 20D) are right-handed threads and the Archimedean screw threads (23B, 23C ) of the second and third propulsion assemblies (20B, 20C) are left-hand threads. Robotic device according to one of the preceding claims, in which each propulsion assembly (20A, 20B, 20C, 20D) further comprises rolling members (24) mounted in pivot connection on the corresponding drum and distributed along the Archimedes screw thread so as to be driven in rotation by contact with the ground during the rotation of the drum.