Rolling ball for a single-spherical-wheel mobile robot

Abstract

The present invention relates to a ball having a spherical outer surface comprising N parts (P1, P2, P3, P4), with N = 2K, K being an integer greater than or equal to 2, the parts all having identical general dimensions, each part comprising a cap-shaped body having an outer face coinciding with the outer sphere, each part comprising three joining edges (B1, B2, B3), each edge being delimited by an arc of a circle, a first joining edge being referred to as the equatorial edge (B1), and second and third joining edges (B2, B3), the angular range of the arc of the equatorial edge being equal to β, with β = 360° / K, each part comprising reinforcing elements, each edge comprising connecting elements. The present invention also relates to a method for assembling the ball and to a single-spherical-wheel mobile robot using such an assembled multi-piece ball.

Description

Ball bearing for mobile robot with single spherical wheel

[0001] The present invention relates to the field of robots, particularly mobile robots, for example, but not exclusively, humanoid robots. More specifically, the invention relates to a mobile robot with a single spherical wheel, said spherical wheel forming the only contact with the ground when the robot moves autonomously or stands motionless in balance.

[0002] The spherical wheel is also referred to here as a 'rolling ball' or simply a 'ball'. The present invention also relates to the structure of the ball in question and its manufacturing process. STATE OF THE ART

[0003] Robots are known to consist of a single spherical wheel (ball) on which the entire robot rests. These types of robots are commonly called "Ballbots." These robots are mobile in all directions using only this spherical wheel, with stability ensured by controlled actuators that act on the ball to rotate it. Three roller wheels interacting with the spherical surface of the ball can be used as actuators.

[0004] In particular, the applicant company presented such robots in humanoid form, called Miroki™ and Miroka™. Document FR3142113 presents certain aspects of these robots.

[0005] The ball bearing for these robots must have sufficient rigidity for the servo control loop using the three roller wheels to function effectively. The ball bearing is made of metal, such as aluminum or steel, using a construction method where two hemispheres are joined together. The weight and moment of inertia of this metal ball bearing are quite substantial and may be considered excessive for certain dynamic situations. Particular attention is also paid to the ball bearing's production cost.

[0006] The ball must resist mechanical wear caused by rough contact surfaces. A high coefficient of friction on its surface and low inertia are advantageous.

[0007] The inventors sought to reduce the weight and moment of inertia of the ball while maintaining good rigidity and a high-quality, non-slip surface finish to ensure proper interfacing with the drive rollers. They also aimed to reduce the ball's production cost. PRESENTATION OF THE INVENTION

[0008] In this context, the present invention relates, according to a first aspect, to a ball, intended to form a spherical wheel for the movement of a mobile robot, having a spherical outer surface, of radius R and centered on a center of the ball, comprising N pieces, with N = 2 x K, K being an integer greater than or equal to 2, the pieces all having identical general dimensions, each piece comprising a cap-shaped body having an outer face coinciding with the outer sphere, each piece comprising three junction edges, each edge being delimited by an arc of a circle having a center of curvature coinciding with the center of the ball, a first junction edge being called equatorial, the second and third junction edges joining at a vertex point, the angular range of the arc of the equatorial edge being equal to β, with β = 360° / K, each piece comprising reinforcing elements, each edge comprising connecting elements.

[0009] It must be understood that the parts in question here are formed as separate parts, which, after assembly, together form the ball bearing.

[0010] Thanks to these features, a multi-piece ball is proposed, consisting of at least four parts, each smaller than a hemisphere. As will be seen later, the parts can be assembled by simply clipping them together (or more generally, by the aforementioned fastening methods). This solution reduces the production cost of the bearing ball. As will be seen later, these parts can be made of plastic.

[0011] We note that the meeting of the equatorial edges of K pieces forms a diametrical circle, which allows the final assembly of the sphere to be carried out from two hemispheres prepared in advance, as will be seen in detail later.

[0012] It should be noted that the proposed solution also reduces the weight and moment of inertia of the ball, which increases the robot's agility and makes the stability control servo loop more robust.

[0013] For the 'ballbot' type application, the spherical surface of the ball should preferably be continuously spherical, without hollows or bumps, without protruding elements or holes, without facets.

[0014] Two adjacent edges meet at a corner of the piece. The piece thus has three edges and three corners. The arc of the circle delimiting the second edge has a measure of 90°, and the arc of the circle delimiting the third edge also has a measure of 90°.

[0015] Reinforcing elements provide good rigidity and resistance to stress on the assembled ball; they can take several forms, which will be discussed later.

[0016] In one embodiment, each edge includes a docking plane. The docking plane of the second edge is perpendicular to the docking plane of the first edge, and the docking plane of the third edge is perpendicular to the docking plane of the first edge. At the vertex opposite the first edge, the docking plane of the second edge is angularly separated from the docking plane of the third edge by an angle β, where β = 360° / K. Thus, for K=3, β = 120°, which is an obtuse angle. For K=5, β = 72°. For K=6, β = 60°. For K=2, β = 180°. The advantageous case K=4 is discussed later.

[0017] Plane-on-plane abutment at the edges joining two adjacent pieces allows for the efficient absorption of compressive forces, which can exist particularly when a force is exerted on the ball.

[0018] The two right angles are part of a simple geometric definition. Such a shape is easy to demold. If K=4, the vertex angle between the docking plane of the 2nd edge and the docking plane of the 3rd edge is also perpendicular, and therefore there are 3 right-angled corners.

[0019] In one embodiment, N = 8 is chosen, which gives K = 4 and therefore β = 90°. This results in a distinctive shape for each piece, with a right angle at each corner, and an overall equilateral triangular shape. The three edges are geometrically identical, and the piece can be mounted in any orientation. Each edge can be described as 'equatorial' because each edge, along with three other edges in the same plane, forms a great diametral circle that can be called the 'equator'.

[0020] In one embodiment, the connecting elements comprise a male and a female component. The male and female forms cooperate to lock together during assembly. These are easily recognizable and intuitive shapes to assemble.

[0021] Depending on the design, the connecting elements can take the form of hooks. Any clipping system with irreversible or nearly irreversible locking can be used to form the means of connecting the edges together.

[0022] According to one design, the N parts are strictly identical. Therefore, all the parts can be produced from a single mold. The tooling required is thus reduced, both in number and size. Indeed, the size of the part to be formed is on the order of the radius R, and not the diameter D=2R as would be the case if a hemisphere were to be formed.

[0023] This solution of strictly identical parts can be applied for all values ​​of K from 2 onwards, it is not only valid for K=4.

[0024] According to another aspect of the invention, the N parts are made of plastic. The use of a plastic molding process makes it possible to obtain complex shapes in the parts that constitute the sphere. The use of plastic also results in a lighter assembled sphere with a lower moment of inertia than a metal solution. Using plastic to produce a plurality of moderately sized parts also results in a lower production cost.

[0025] Depending on the specific design, a coating may be applied, obtained for example by an overmolding or dipping process, which then forms the outer layer of the ball. In some specific designs, the parts are made of polymer, for example, fiber-reinforced polyamide.

[0026] It is noted that the ball does not need to be perfectly balanced given the low rotational speeds involved; there is no imbalance effect.

[0027] In one embodiment, the reinforcing elements are formed as a network of ribs projecting inwards towards the sphere. Some ribs are parallel to an edge of the part. The rib network can form a matrix of intersecting ribs. These ribs significantly limit the deformation of the part, particularly its bending.

[0028] In one embodiment, the sphere may further comprise a core, each of the N pieces being radially supported on the core directly or indirectly via one or more supports. The core is placed at the center of the sphere.

[0029] This contributes to the overall rigidity of the assembled ball. The ball's deflection under crushing stress is greatly reduced due to the diametrical transfer of forces.

[0030] We can aim for a deflection criterion of less than 3 mm, or even less than 2 mm, under a diametral crushing force of 100 Newton for a ball of 40 cm in diameter, without these values ​​being limiting.

[0031] In one embodiment, advantageously, the ball has a radius R of at least 15 cm and a weight of at most 1.5 kg. This results in a lightweight and rigid ball of sufficient size, well suited to the function of a ground interface for a mobile bale-type robot.

[0032] In another embodiment, the sphere has a radius R of at least 12 cm and a weight of at most 1 kg. In yet another embodiment, the sphere has a radius R of at least 18 cm and a weight of at most 2 kg.

[0033] One characteristic of the sphere is that it is hollow, not solid. A solid sphere would have a greater weight. It is also noted that the sphere is not pressurized and contains no active organs.

[0034] The present invention relates, according to a second aspect, to a method of assembling a ball as defined above, according to which K=N / 2 pieces are assembled together to form a first hemisphere, then the remaining N / 2 pieces are assembled together to form a second hemisphere, then the first and second hemispheres are assembled together, the ball thus assembled having a spherical outer surface.

[0035] The assembly described above is preferably non-dismantable. It would be necessary to break the surface to access the connecting means in order to unlock them.

[0036] According to one feature, the assembly requires no welding or screwing.

[0037] The present invention relates, according to a third aspect, to a mobile robot of the type with a single spherical wheel, said spherical wheel being formed by a ball conforming to the characteristics described above. PRESENTATION OF THE FIGURES

[0038] The invention will be better understood upon reading the following description, given solely by way of example, and referring to the accompanying drawings given by way of non-limiting examples, in which identical references are given to similar objects and on which:

[0039] This is a schematic representation of the lower part of an example of a mobile robot with a single spherical wheel, in which the present invention can be implemented;

[0040] Lamontre an example of a multi-piece ball, according to a first embodiment, with 8 identical pieces, in exploded view, with one piece in transparency;

[0041] Lamontre schematically shows the reference frame of the pieces in the sphere, with two opposite pieces visible in the upper hemisphere;

[0042] Laillustre, seen from above, shows an example of balls with 8 identical pieces;

[0043] Laest analogue to laet shows in top view an example of a ball with 8 identical pieces, with a 45° offset of one hemisphere relative to the other;

[0044] Lamontre, according to the first embodiment, one of the parts in isolation, seen from the center of curvature;

[0045] Lamontre schematically assembles the parts into a ball with 8 parts / quarters;

[0046] Laillustre a variant of the position of the male and female organs arranged in alternating materials;

[0047] Laillustre les angles aux coins de la pièce;

[0048] Laillustre provides examples of means of joining edges of parts;

[0049] Laillustre an embodiment with a core and radial support elements on the core;

[0050] Laillustre en vue de haut un mode de embodiment avec six pièces, i dit K=3 et β = 120°.

[0051] Laillustre en vue de perspective le mode de réalisation de laavec six pièces.

[0052] Laillustre en vue de coupe le mode de fabrication de laavec six pièces.

[0053] Laillustre en vue de haut un mode de embodiment avec 10 pièces, dit K=5 et β = 72°.

[0054] Laillustre en vue de haut un mode de embodiment avec 12 pièces, dit K=8 et β = 50°.

[0055] Laillustre en vue de haut un mode de embodiment avec 16 pièces, dit K=8 et β = 45°.

[0056] It should be noted that the figures set out the invention in detail to enable implementation of the invention; although not limiting, said figures serve in particular to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0057] The invention relates to a mobile robot with a single spherical wheel, said spherical wheel forming the sole contact with the ground when the robot moves autonomously or stands upright in stationary equilibrium. The lower part of the robot is shown in Figure 1. The robot's leg 10 rests on the ball bearing 1, which rests on the ground. A closed-loop control system with known stability allows the robot to remain upright continuously without any other point of support on the ground. The robot's leg 10 bears on the ball bearing 1 via three control roller wheels, labeled 11, 12, and 13, respectively. Each roller wheel comprises rollers 16 arranged on the circumference of the wheel with an axis perpendicular to the general axis of the wheel A. The wheel 11 is driven by a motor 15 and exerts a tangential force.The coordinated control of the 3 wheel motors allows the ball to be rotated in any direction according to the position correction necessary for stability and maintaining the vertical posture.

[0058] The ball 1 must resist mechanical wear caused by the rough contact surfaces of the drive wheel rollers. A high coefficient of friction on its surface and low inertia are advantageous. The ball 1 must exhibit good rigidity and high elastic stiffness. The first mode of deformation corresponds to crushing under the robot's vertical weight; the deformation must be as small as possible. Stability control is all the more robust if the ball remains perfectly spherical while rotating. Its apparent elastic modulus must be uniform in all radial directions.

[0059] For example, the diameter D of the ball can be between 20 cm and 50 cm, without these values ​​being limiting.

[0060] According to the first embodiment illustrated in Figure 1, the sphere is composed of 8 identical pieces. The pieces in question are respectively identified as P1, P2, P3, P4, P5, P6, P7, P8 and generically by the reference 2.

[0061] Each piece 2 comprises a cap-shaped body with an outer face coinciding with the outer sphere of the ball to be formed. As shown in Figures 6 and 9, each piece has three connecting edges labeled B1, B2, and B3. Here, each edge forms the interface with only one adjacent piece. We will see later that, according to certain variations, an edge can form an interface with two adjacent pieces. As shown in Figures 6 and 9, the first edge B1 and the third edge B3 join at a corner E1, the first edge B1 and the second edge B2 join at a corner E2, and the second edge B2 and the third edge B3 join at a corner E3.

[0062] As can be seen in the image, each edge is delimited by an arc of a circle C having a center of curvature coinciding with the center of the ball CB, or in other words a radius of curvature corresponding to the radius R of the ball to be formed.

[0063] This also illustrates a spherical coordinate system that can be used to geometrically describe the multi-piece sphere. The origin of the coordinate system is the center of the sphere CB. An azimuth angle θ is defined with respect to an arbitrary reference direction θ=0. An elevation angle Φ is defined with respect to an arbitrary reference direction Φ=0. The sphere is defined as all points M with coordinates θ, Φ that lie at a given distance R from the center of the sphere CB. By convention for this description, the equator is denoted as the circle of points with coordinates Φ=0. Each of the poles Φ=+90° and -90° is designated as a 'vertex'.

[0064] The first junction edge B1 is called 'equatorial' purely by convention. The second junction edge B2 and the third junction edge B3 join at a point called here vertex S, which is located opposite the first junction edge.

[0065] The first joining edge B1 presents a berthing plane A1. The second joining edge B2 presents a berthing plane A2 and the third joining edge B3 presents a berthing plane A3. After assembly, the berthing planes of two adjacent edges form a plane-on-plane interface that allows compressive forces to be absorbed without substantial deformation.

[0066] The berthing plans are also equipped with means of connection to link the sides which are opposite each other.

[0067] The angular range of the arc of the equatorial edge B1 is 90° here. The arc of the circle delimiting the second edge B2 and the third edge B3 also has a range of 90°.

[0068] According to a general definition of the present invention, the angular range of the arc of the equatorial edge is an angle called β, with β= 360° / K, with K=4 for the first embodiment.

[0069] According to various designs, each piece includes 6 reinforcing elements which will be seen in detail later.

[0070] Furthermore, each edge includes elements for connecting to other adjacent edges. These connecting means include positioning elements and retention or locking elements.

[0071] According to the example illustrated in figures 2,3,6,7,10, the retention elements3 comprise a male organ5 and a female organ4. The male and female forms (respectively identified asMetF) cooperate together to lock into each other during assembly.

[0072] The female form can be understood as an orifice with a non-return shoulder 42; the male form 5 can include a hook 52 which comes to rest against the non-return shoulder of the female form.

[0073] The retention elements 3, once locked, prevent the adjacent edges from separating. The circles delimiting the edges thus remain against each other without gaps or gaps.

[0074] Furthermore, positioning elements consisting of complementary shapes in the berthing planes may be provided. For example, as illustrated in the figure, the berthing plane A2 includes a projecting shape 53 (generally a projection or convex shape), and the opposite berthing plane A3 includes a recessed shape 43 (generally a depression or concave shape complementary to the shape of the projection opposite).

[0075] These positioning elements prevent radial shift of one edge relative to the other under radial force supported by only one edge.

[0076] Variants concerning the retention elements have been illustrated. In the detail on the left, in zone 10A, the hook 54 is arranged on the radially inner side of the edge and protrudes tangentially from the cap. The hook is anchored to a notch 44 in the opposite edge.

[0077] On the detail on the right, in zone 10B, the retention elements are formed like male hooks55 that hook onto each other.

[0078] According to an advantageous embodiment of the invention, all parts can be strictly identical. This is the case in the illustrated example of the first embodiment. This can also apply for K other than 4, as will be seen later.

[0079] With reference to the terrestrial analogy presented at the, the room in the southern hemisphere corresponds to the opposite room in the northern hemisphere after a 180° rotation, the docking plane passing through the equatorial circle EQ.

[0080] According to various designs, the parts are made of plastic.

[0081] Advantageously, the parts are manufactured from a single mold if they are all identical. Of course, depending on the different solutions for the connecting elements, there could be two different molds.

[0082] The molding injection points are advantageously located in an inner radial area of ​​the cap, so that the outer spherical surface of the cap is free of sprue and the need for rework.

[0083] Preferably, the sphere is formed simply by assembling the molded parts. However, it is possible to apply a coating to cover the entire spherical surface of the assembled plastic parts. This coating can be applied by overmolding or dipping. It can serve several purposes, particularly if the sphere is used in a context other than a mobile robot with a single spherical wheel.

[0084] The reinforcing elements are formed as a network of ribs projecting inwards towards the sphere. Some ribs are parallel to an edge of the part. The rib network can form a matrix of intersecting ribs.

[0085] The arrangement of the ribs in the radially inner part of the cap complements the berthing planes located at the edges of the part.

[0086] As can be seen in the diagram, the cap then has a radial thickness denoted DR which can typically be between 0.1 x R and 0.2 x R.

[0087] According to another configuration illustrated in particular in Figure 1, a core 7 can be provided in a central position within the sphere. Each of the parts can include arms 81, 82 directed radially inwards which contact the core 7 as shown on the left half of Figure 1. In the case of an integral mold, there could be only one arm.

[0088] In the right part of the diagram, another solution has been represented where the radial support is formed by a strut shaped as a separate piece.

[0089] Since each of the parts is radially supported on the core, it is easy to understand that the first mode of elastic deformation of the ball, namely crushing, is strongly limited by the presence of the diametrical transfer of the forces which pass through the core.

[0090] We note that the corner chamfers25 ensure that the contact of the circular arcs of the opposite edges, and that the contact of the corners at the vertices are not hindered by a contact located further inside the sphere.

[0091] Figures 12 to 14 illustrate a second embodiment with a multi-piece ball of 6 pieces, i.e. K=3. We note that the upper hemisphere is offset by 60° with respect to the lower hemisphere, that is to say that the edges between the pieces of the upper hemisphere are not aligned with the edges between the pieces of the lower hemisphere.

[0092] Therefore, in this configuration there are no vertex points with 4 branches / segments, only vertex points with 3 segments (for example, intersection 9en). Note that a particular edge interfaces with two other edges in this configuration.

[0093] Conversely, in the configuration of the first embodiment with K=4, all vertices are 4-segment vertices (cfet 4).

[0094] A specific arrangement of the retention mechanisms, in the form of male and female parts, is illustrated. An alternation of these male and female parts is observed. The parts can interlock when one part is rotated 180° relative to the median axis of the edge PMB. Furthermore, it is noted that if an angular offset of β / 2 is applied, the complementary parts end up facing each other, and interlocking is possible. This allows for a general offset of one hemisphere relative to the other, by an angle of β / 2, as illustrated in Figures 5 and 13.

[0095] Thus, for the embodiment shown in figures 12 to 14, all the parts are identical to each other.

[0096] The assembly process includes preparing one hemisphere as illustrated in the figure, then preparing another hemisphere, and then assembling the two hemispheres.

[0097] Figure 1 illustrates an embodiment with 10 pieces, i.e. K=5 and β = 72°. Figure 2 illustrates an embodiment with 12 pieces, i.e. K=8 and β = 50°. Figure 3 illustrates an embodiment with 16 pieces, i.e. K=8 and β = 45°.

[0098] It is preferable for the ball to have a continuously spherical surface, however it is not excluded to provide a very small through hole (diameter of the order of 0.5 mm) to be able to pass a suspension wire through in order to suspend the parts and / or the ball in particular during manufacturing operations.

[0099] It should be noted that the ball proposed here can be used in a context other than that of a spherical wheel for moving a mobile robot.

[0100] It should also be noted that the invention is not limited to the embodiments described above. Indeed, it will become apparent to a person skilled in the art that various modifications can be made to the embodiments described above, in light of the information just provided.

[0101] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiment set forth in this description, but shall be interpreted to include all equivalents which can be foreseen by a person skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

A sphere (1), intended to form a spherical wheel for the movement of a mobile robot, having a spherical outer surface of radius R centered on a sphere center (CB), comprising N parts (P1, P2, P3, P4), with N = 2 x K, K being an integer greater than or equal to 2, the parts all having identical overall dimensions, each part comprising a cap-shaped body having an outer face coinciding with the outer sphere, each part comprising three connecting edges (B1, B2, B3), each edge being delimited by an arc of a circle having a center of curvature coinciding with the sphere center (CB), a first connecting edge (B1) being called equatorial, the second and third connecting edges (B2, B3) joining at a vertex point (S), the angular range of the arc of the equatorial edge being equal to β, with β = 360° / K, each part comprising reinforcing elements (6), each edge comprising connecting elements (3). Ball (1) according to claim 1, wherein each edge comprises a berthing plane, the berthing plane (A2) of the second edge being perpendicular to the berthing plane (A1) of the first edge, the berthing plane (A3) of the third edge being perpendicular to the berthing plane of the first edge (A1). Ball according to any one of claims 1 to 2, in which N = 8, i.e. K=4 and therefore β = 90°. Ball according to any one of claims 1 to 3, wherein the connecting elements comprise a male organ (5) and a female organ (4). Ball according to any one of claims 1 to 4, wherein the N pieces are strictly identical. Ball according to any one of claims 1 to 5, wherein the N parts are made of plastic material. Ball according to any one of claims 1 to 6, wherein the reinforcing elements (6) are formed as a network of ribs projecting into the interior of the sphere. Ball according to any one of claims 1 to 7, further comprising a core (7), each of the N pieces being radially supported on the core directly or indirectly through one or more supports (8). Ball according to any one of claims 1 to 8, having a radius R of at least 15 cm and a weight of at most 1.5 kg. Method of assembling a ball according to any one of claims 1 to 9, wherein K=N / 2 pieces are assembled together to form a first hemisphere, then the remaining N / 2 pieces are assembled together to form a second hemisphere, then the first and second hemispheres are assembled together, the ball thus assembled having a spherical outer surface. Mobile robot of the type with a single spherical wheel, said spherical wheel being formed by a ball conforming to any one of claims 1 to 10.

Images