Joint for a robot comprising a cable transmission

Abstract

The present invention relates to a joint (2) for a robot, comprising: • a proximal segment (4); • a distal segment (6) connected to the proximal segment (4) via a pivot connection, the distal segment (6) being configured to pivot about an axis of the pivot connection between a first position of the joint (2) and a second position of the joint (2); • a motor configured to actuate a cable transmission (12), the cable transmission (12) comprising an upper part which is secured to both the proximal segment (4) and the distal segment (6) and a lower part secured to both the proximal segment (4) and the distal segment (6); • the joint (2) being characterised in that the pivot connection is formed by a toothed portion of the proximal segment (4) meshing with a toothed portion of the distal segment (6).

Description

Robot joint including a cable transmission

[0001] The present invention relates to the field of robots, in particular humanoid robots.

[0002] More specifically, the invention relates to a joint of a limb of such a robot, in particular an upper limb, for example an elbow joint. STATE OF THE ART

[0003] A known prior art joint for a robot's upper limb, particularly for a humanoid robot, is comparable to a human elbow. Such a joint generally comprises a proximal and a distal segment, connected by a pivot joint or a ball joint, with the distal segment pivoting around this joint to mimic elbow flexion or extension.

[0004] To animate such a joint and achieve the pivoting movement, it is common to use an electric motor, such as a servomotor, driving a cable transmission of the joint. Cable transmissions offer the advantage of ensuring high precision in matching the movement to a predetermined setpoint. Cable transmissions also allow, through the use of pulleys, for force multiplication. In the case of a robot joint, this results in the possibility of manipulating heavier objects using the same actuator mounted on a traditional joint, such as a bearing joint.

[0005] However, cable drives also have reliability limitations, particularly because they require optimal cable alignment relative to the loads being handled. Indeed, if the misalignment is too pronounced, the cables can slip, damaging the drive system. Furthermore, cable drives can also be larger than other types of traditional linkages, reducing their range of possible applications.

[0006] The invention aims to remedy all or part of the drawbacks of the prior art, in particular by proposing an articulation comprising a compact cable transmission that is resilient to cable misalignments. PRESENTATION OF THE INVENTION

[0007] More specifically, the invention relates to a joint for a robot, in particular a humanoid robot, comprising: a proximal segment configured to be connected to a body of the robot; a distal segment connected to the proximal segment via a pivot joint, the distal segment being configured to pivot around an axis of the pivot joint between a first position of the joint in which the proximal segment and the distal segment are aligned and a second position of the joint in which the proximal segment and the distal segment are substantially orthogonal;a motor configured to actuate a cable transmission of the joint, the cable transmission comprising an upper part attached on one side to the proximal segment and on the other side to the distal segment, the cable transmission further comprising a lower part attached on one side to the proximal segment and on the other side to the distal segment, a length of the upper part of the cable transmission being maximum and a length of the lower part of the cable transmission being minimum in the first position of the joint, the length of the upper part of the cable transmission being minimum and the length of the lower part of the cable transmission being maximum in the second position of the joint;

[0008] The joint is remarkable in that the pivot joint is formed by at least one toothed portion of the proximal segment in mesh with a toothed portion of the distal segment, the upper part of the cable transmission and the lower part of the cable transmission being located on either side of a first reference plane containing the axis of the pivot joint.

[0009] According to the invention, the cable transmission comprises a drum fixed in rotation to the motor and further comprises a cable.

[0010] Furthermore, the motor drives the drum in rotation around an axis of rotation substantially orthogonal to the axis of the pivot joint. The cable transmission also includes idler pulleys that allow the cable to be wound and unwound around the drum. In this configuration, the resulting joint is more compact, as the motor can be housed in the proximal segment. Moreover, this arrangement facilitates simultaneous winding and unwinding of the cable.

[0011] Thanks to this combination of features, such a cable joint offers the advantage of being significantly more robust, as the alignment necessary for cable guidance is ensured by at least one meshing contact between the distal and proximal segments. Furthermore, such a joint also has a reduced footprint, as the cable transmission can extend within a volume defined by the joint segments. In addition, such a joint offers the advantage of being highly reversible, not only for moving from one position to another but also for adopting any intermediate position between the first and second positions. Moreover, "reversibility" can also be understood as the ability to be actuated by external forces when the joint's motor is disengaged.Such reversibility allows, in the case of a humanoid robot joint, for a more faithful imitation of the kinetics of a human joint.

[0012] Advantageously, each segment comprises a first toothed portion and a second toothed portion. The first and second toothed portions of each segment mesh together, respectively, such that the axis of the pivot joint passes through points of meshing between the first and second toothed portions. In this configuration, force transmission occurs via two additional contacts besides the cable transmission, thus improving the service life of the joint components and significantly enhancing the alignment required for optimal cable transmission operation.

[0013] Advantageously, the cable of the cable transmission comprises an upper and a lower portion, each attached to an anchor point on the distal segment. The upper portion of the cable is configured to wrap around the drum, and the lower portion is configured to unwind from the drum when the joint moves from the first to the second position. In this configuration, the cable transmission can be achieved with a single cable, simplifying the joint's fabrication.Furthermore, the minimum and maximum lengths of the upper and lower sections of the cable transmission are directly proportional to the lengths of the upper and lower portions that wind and unwind from the drum. This results in the possibility of achieving high precision in controlling the joint to obtain a desired position, for example, an intermediate position between the first and second positions of the joint.

[0014] Advantageously, the upper part of the cable transmission comprises at least one pair of upper pulleys, each upper pulley of a pair being fixed to a different segment of the joint, the upper portion of the cable being configured to run between the upper pulleys. In such a configuration, a gear ratio for the cable-transmitted forces can be advantageously chosen according to the number of upper pulley pairs selected. In this embodiment, the length of the upper part of the cable transmission can be defined as the center-to-center distance between the two upper pulleys of the same pair.

[0015] Advantageously, the lower part of the cable transmission comprises at least one pair of lower pulleys, each lower pulley of a pair being fixed to a different segment of the joint, the lower portion of the cable being configured to run between the lower pulleys. In such a configuration, a gear ratio for the forces transmitted by the cable can be advantageously chosen according to the number of pairs of lower pulleys selected. In this embodiment, the length of the lower part of the cable transmission can be defined as the center distance between the two lower pulleys of the same pair.

[0016] Advantageously, a spacer is configured to maintain contact between the distal and proximal segments. In such a configuration, the robustness of the joint is significantly improved, as contact between the toothed portions and the alignment of the segments can be maintained even when the tension in the cable transmission is zero, for example, in the event of cable breakage.

[0017] Advantageously, the length of the spacer defines the center distance of the interlocking mechanism between the toothed portion of the proximal segment and the toothed portion of the distal segment. In such a configuration, the robustness of the joint is significantly improved, as the center distance of the interlocking mechanism is kept constant by the spacer, regardless of the angle formed by the segments relative to each other.

[0018] Advantageously, the joint comprises a first shell configured to enclose at least partially the proximal segment of the joint, a second shell configured to enclose at least partially the distal segment of the joint, and a third shell configured to enclose at least partially both segments simultaneously. In such a configuration, the mechanical components of the joint are protected from the external environment without the shell interfering with the mobility of the segments.

[0019] According to another aspect of the invention, it relates to a robot, in particular a humanoid robot, comprising: a body; a first joint according to one of the preceding claims, said joint being connected to the body of the robot via the proximal segment of the first joint; a second joint, said second joint being connected to the first joint via the distal segment of the first joint. PRESENTATION OF THE FIGURES

[0020] 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:

[0021] This is a schematic perspective representation of a robot joint according to a first aspect of the invention;

[0022] Laest is a schematic front view representation of the joint, in a withdrawn position from a plurality of the joint's shells;

[0023] This is a schematic diagram in front view of the joint, in a first position of the joint;

[0024] This is a schematic diagram in front view of the joint, in a second position of the joint;

[0025] This is a schematic top-view representation of the joint of the;

[0026] This is a partial schematic representation of a joint according to another embodiment of the invention.

[0027] 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

[0028] The invention relates, in particular, according to a first aspect, to a robot (not illustrated), specifically a humanoid robot. According to another aspect of the invention, the robot comprises a joint 2 as illustrated in the figure, forming a robotic arm of the robot.

[0029] The joint 2 comprises a proximal segment 4 and a distal segment 6. In the case of a humanoid robot, the proximal segment 4 can, for example, be an arm (comparable to a human humerus) and the distal segment 6 can, for example, be a forearm.

[0030] In this diagram, joint 2 is at least partially enclosed by a plurality of shells 32a, 32b, 32c, comprising a first shell 32a, a second shell 32b, and a third shell 32c. The first shell 32a is configured to at least partially enclose the proximal segment 4. The second shell 32b is configured to at least partially enclose the distal segment 6. The third shell 32c is configured to at least partially enclose both segments 4 and 6 simultaneously. Thus, the segments and mechanical components of joint 2 are advantageously protected.

[0031] Figure 1 illustrates the joint from a front view. For clarity, the plurality of shells 32a, 32b, 32c is not shown. Segments 4, 6 can each be formed by a single flat plate or by a plurality of assembled flat plates defining an internal housing for the joint 2, as illustrated here.

[0032] Segments 4 and 6 are connected by a pivot joint. This joint has a pivot axis 100, represented by a point in Figures 2, 3, and 4 due to the chosen viewpoint. The pivot axis 100 is substantially orthogonal to both the proximal segment 4 and the distal segment 6. Furthermore, the pivot joint is such that the distal segment 4 is configured to pivot around the axis of the pivot joint 100 between a first position in which the proximal segment 4 and the distal segment 6 are aligned and a second position in which the proximal segment 4 and the distal segment 6 are substantially orthogonal. Naturally, the joint 2 can assume any intermediate position between these two limiting positions.

[0033] The joint 2 also includes a motor 10, for example an electric motor. Here, the motor 10 is received by the housing of the proximal segment 4. The joint 2 also includes a cable transmission 12. The cable transmission 12 includes an upper part 14 fixed to the proximal segment 4 on one side and to the distal segment 6 on the other. The cable transmission 12 also includes a lower part 16 fixed to the proximal segment 4 on one side and to the distal segment 6 on the other.

[0034] The motor 10 is configured to actuate the cable transmission 12, so that a mechanical tension within the cable transmission induces the pivoting of the distal segment 6 relative to the proximal segment 4 to move from one position to another or to adopt an intermediate position.

[0035] When the joint 2 is in the first position, particularly as illustrated in the figure (and this is not specific to the embodiment presented), the length of the upper part 14 of the cable transmission 12 is at its maximum. In other words, the ends of the upper part 14 of the cable transmission 12 are as close to each other as possible in this position. Conversely, the length of the lower part 16 of the cable transmission 12 is at its minimum in the first position. In other words, the ends of the lower part 16 of the cable transmission 12 are as close to each other as possible in this position.

[0036] Similarly, in the second position of the joint 2, representing the same embodiment, the length of the upper part 14 of the cable transmission 12 is minimal. In other words, the ends of the upper part 14 of the cable transmission 12 are as close to each other as possible in this position. Conversely, the length of the lower part 16 of the cable transmission 12 is maximal in the second position. In other words, the ends of the lower part 16 of the cable transmission 12 are as close to each other as possible in this position.

[0037] Joint 2 is notable in particular because the pivot joint is formed by at least one toothed portion 18 of the proximal segment 4 meshing with a toothed portion 20 of the distal segment. The term "meshing" refers to at least one contact between straight teeth of the toothed portions 18 and 20 of the same module and, a fortiori in this embodiment, of identical diameters and the same number of teeth. It is thus understood that this movable contact lies on the axis of the pivot joint 100. Furthermore, the axis of the pivot joint 100 also defines a reference plane 200 of the joint, represented by a segment in the figures due to the chosen viewpoint, separating joint 2 into a so-called "upper" part and a so-called "lower" part.

[0038] To allow the pivoting movement around the axis of the pivot link 100 of the distal segment 6 relative to the proximal segment 4, the upper part 14 of the cable transmission 12 and the lower part 16 of the cable transmission 12 are thus located on either side of the reference plane 200.

[0039] Thanks to this combination of features, such a cable joint 2 has the advantage of being significantly more robust, as the alignment necessary to guide the cable transmission 12 is guaranteed by at least one meshing contact between the distal segment 4 and the proximal segment 6. Furthermore, such a joint 2 also has a reduced footprint, as the cable transmission 12 can extend within a volume defined by the segments 4 and 6 of the joint. In addition, such a joint has the advantage of being highly reversible, not only for moving from one position to the other but also for adopting any intermediate position between the first and second positions. Moreover, "reversibility" can also be understood as the ability to be actuated by external forces when the joint's motor 10 is disengaged.Such reversibility allows, in the case of a humanoid robot joint, for a more faithful imitation of the kinetics of a human joint.

[0040] Advantageously, and as illustrated, each segment 4,6 can comprise a first toothed portion 18,20 and a second toothed portion 18,20. The first toothed portions 18,20 and the second toothed portions 18,20 of each segment 4,6 mesh with each other. It is understood that these two contacts lie on the axis of the pivot joint 100. In such a configuration, the transmission of forces occurs via two additional contacts besides the cable transmission 12, thus improving the service life of the components of the joint 2 and significantly enhancing the alignment necessary for the optimal operation of the cable transmission 12.

[0041] In the embodiment illustrated on the and on the, the cable transmission 12 includes a drum 22. The drum 22 is rotationally fixed to the motor 10 which drives it in rotation.

[0042] The cable transmission 12 also includes a single cable 24. The cable 24 comprises an upper and a lower portion, each attached to an anchor 26 of the distal segment 6. Preferably, each portion of cable 24 is attached to a separate anchor 26. The upper portion of cable 24 is configured to wind around the drum 22, and the lower portion of cable 24 is configured to unwind from the drum 22 when the joint 2 moves from the first position to the second position. This generates a force on the anchor point 26 in the upper part of the joint 2, resulting in a counterclockwise rotation of the distal segment 4, in other words, shortening the length of the upper portion 14 of the cable transmission 12 and lengthening the length of the lower portion 16 of the cable transmission 12.

[0043] Similarly, the upper portion of cable 24 is configured to unwind from the drum 22, and the lower portion of cable 24 is configured to wind around the drum 22 when the joint 2 moves from the second position to the first position. This generates a force on the anchor point 26 in the lower part of the joint 2, resulting in a clockwise rotation of the distal segment 4, in other words, lengthening the upper portion 14 of the cable transmission 12 and shortening the lower portion 16 of the cable transmission 12.

[0044] In such a configuration, the cable transmission 12 can be made with a single cable 24, simplifying the manufacture of the joint 2. In addition, the minimum and maximum lengths of the upper and lower parts of the cable transmission 12 are directly proportional to the lengths of the upper and lower portions winding and unwinding from the drum 22. This results in the possibility of obtaining high precision in the control of the joint 2 to obtain a desired position, for example an intermediate position between the first and second positions of the joint.

[0045] Naturally, the rolling of one portion and the unrolling of the other portion happen simultaneously.

[0046] In the embodiment illustrated, for example, in Figure 1, the upper portion 14 of the cable transmission 12 comprises at least one pair of upper pulleys 28. Each upper pulley 28 of a pair of upper pulleys 28 is fixed to a different segment 4, 6 of the joint 2. The upper portion of the cable 24 is configured to run between the upper pulleys 28. In such a configuration, a gear ratio for the forces transmitted by the cable can be advantageously chosen depending on the number of pairs of upper pulleys 28 selected. In this embodiment, the length of the upper portion 16 of the cable transmission 12 can be defined as the center distance between the two upper pulleys 28 of the same pair.

[0047] In the illustrated embodiment, the lower part 16 of the cable transmission 12 comprises at least one pair of lower pulleys 30. Each lower pulley 30 of a pair of lower pulleys 30 is fixed to a different segment 4,6 of the joint 2. The lower portion of the cable 24 is configured to run between the lower pulleys 30.

[0048] Preferably, the upper and lower parts 14,16 of the cable transmission 12 comprise the same number of pulleys, so that the multiplication of forces is symmetrically distributed on either side of the reference plane 200.

[0049] As illustrated, and optionally, the motor 10 drives the drum 22 in rotation about an axis of rotation substantially orthogonal to the axis of the pivot joint 100 of the articulation. Thus, the cable transmission 12 further includes return pulleys 34 allowing the cable 24 to be wound and unwound around the drum 22 in the direction described. In such a configuration, the resulting articulation 2 is more compact, as the motor 10 can be housed in the proximal segment 4. Moreover, this arrangement facilitates the simultaneous winding and unwinding of the cable 24.

[0050] To further guide the cable 24, the cable transmission 12 may include rollers or bearings to obtain an optimal angle for winding the cable around the various pulleys described.

[0051] Figure 1 illustrates a joint according to another embodiment of the invention. For clarity, the cable 24 is not shown but should be considered as being present within the cable transmission 12. In this embodiment, the joint 2 advantageously comprises a spacer 36 configured to maintain contact between the distal segment 6 and the proximal segment 4. In such a configuration, the robustness of the joint 2 is significantly improved, as contact between the toothed portions 18, 20 and the alignment of segments 4, 6 with each other can be maintained even when the tension in the cable transmission 12 is zero, for example, in the event of a break in the cable 24. Advantageously, a length of the spacer 36 defines a center distance of the meshing between the toothed portion 18 of the proximal segment 4 and the toothed portion 20 of the distal segment 4.In such a configuration, the robustness of the joint 2 is significantly improved, as the center distance of the meshing is kept constant by the spacer 36, regardless of the angle formed by the segments 4, 6 with respect to each other. Preferably, the spacer 36 is connected to each of the segments 4, 6 by a pivot joint. Thus, the spacer 36 neither contributes to nor impedes the transmission of forces between the segments 4, 6 as long as the tension in the cable transmission is non-zero.

[0052] It should also be noted that the invention is not limited to the embodiments described above. Indeed, it will be 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.

[0053] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiments set forth in this description, but shall be interpreted as including 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

Articulation (2) for robot, in particular humanoid, comprising: a proximal segment (4) configured to be connected to a body of the robot; a distal segment (6) connected to the proximal segment (4) via a pivot joint, the distal segment (6) being configured to pivot about an axis of the pivot joint (100) between a first position of the joint (2) in which the proximal segment (4) and the distal segment (6) are aligned and a second position of the joint (2) in which the proximal segment (4) and the distal segment (6) are substantially orthogonal;a motor (10) configured to actuate a cable transmission (12) of the joint (2), the cable transmission (12) comprising an upper part (14) attached on one side to the proximal segment (4) and on the other side to the distal segment (6), the cable transmission (12) further comprising a lower part (16) attached on one side to the proximal segment (4) and on the other side to the distal segment (6), a length of the upper part (14) of the cable transmission (12) being maximum and a length of the lower part (16) of the cable transmission (12) being minimum in the first position of the joint (2), the length of the upper part (14) of the cable transmission (12) being minimum and the length of the lower part (16) of the cable transmission (12) being maximum in the second position of the joint (2);the joint (2) being characterized in that: the pivot joint is formed by at least one toothed portion of the proximal segment (4) meshing with a toothed portion of the distal segment (6), the upper part (14) of the cable transmission (12) and the lower part (16) of the cable transmission (12) being situated on either side of a first reference plane (200) containing the axis of the pivot joint (100); the cable transmission (12) comprises a drum (22) rotationally fixed to the motor (10) and further comprises a cable; the motor (10) drives the drum (22) in rotation about an axis of rotation substantially orthogonal to the axis of the pivot joint (100) of the joint (2), the cable transmission (12) further comprising return pulleys (34) allowing the winding and unwinding of the cable around the drum (22). Articulation (2) according to claim 1, wherein each segment comprises a first toothed portion and a second toothed portion, the first toothed portions of each segment and the second toothed portions of each segment being respectively meshed together so that the axis of the pivot joint (100) passes through points of meshing respectively of the first toothed portions together and of the second toothed portions together. Joint (2) according to any one of the preceding claims, wherein the cable of the cable transmission (12) comprises an upper portion and a lower portion each integral with an anchorage (26) of the distal segment (6), the upper portion of cable being configured to wind around the drum (22) and the lower portion of cable being configured to unwind from the drum (22) in the case where the joint (2) moves from the first position to the second position, the upper portion of cable being configured to unwind from the drum (22) and the lower portion of cable being configured to wind around the drum (22) in the case where the joint (2) moves from the second position to the first position. Articulation (2) according to any one of the preceding claims, wherein the upper part (14) of the cable transmission (12) comprises at least one pair of upper pulleys (28), each upper pulley of a pair of upper pulleys (28) being integral with a different segment of the articulation (2), the upper portion of the cable being configured to run between the upper pulleys (28). Articulation (2) according to any one of the preceding claims, wherein the lower part (16) of the cable transmission (12) comprises at least one pair of lower pulleys (30), each lower pulley of a pair of lower pulleys being integral with a different segment of the articulation (2), the lower portion of the cable being configured to run between the lower pulleys (30). Articulation (2) according to any one of the preceding claims, comprising a spacer (36) configured to maintain contact between the distal segment (6) and the proximal segment (4). Articulation (2) according to claim 6, wherein a length of the spacer (36) defines a center distance of the meshing between the toothed portion of the proximal segment (4) and the toothed portion of the distal segment (6). Joint (2) according to any one of the preceding claims, comprising a first shell (32a) configured to at least partially envelop the proximal segment (4) of the joint (2), a second shell (32b) configured to at least partially envelop the distal segment (6) of the joint (2) and a third shell (32c) configured to at least partially envelop both segments simultaneously. Robot, in particular humanoid, comprising: a body; a first joint (2) according to any one of the preceding claims, said joint (2) being connected to the body of the robot via the proximal segment (4) of the first joint (2); a second joint, said second joint being connected to the first joint (2) via the distal segment (6) of the first joint (2).

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