Actuator for a robotic arm

Abstract

The present invention relates to an actuator for a robotic arm, comprising: • a casing (4) extending along an axis between a first end and a second end; • an output shaft (6) extending between a first end and a second end, the first end of the output shaft being located on the same side as the first end of the casing (4); • a motor comprising a drive shaft (10) extending between a first end and a second end, one of the ends of the drive shaft (10) being located on the same side as the second end of the casing; • a torque sensor (14); • the output shaft (6) and the casing (4) each being secured to the robotic arm by a fixing unit, the fixing units (16) being located on the first side of the actuator.

Description

Actuator for robotic arm

[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 or wrist joint, in particular actuated by an actuator. STATE OF THE ART

[0003] A known prior art is a joint in a robotic arm, particularly in a humanoid robot, comparable, for example, to a human elbow or wrist. In such a case, the joint generally connects a distal segment, for example a forearm, hand, or gripper, to a proximal segment, for example, respectively, a robot arm (anatomically comparable to the human humerus) or forearm.

[0004] Such a joint is generally formed by an actuator comprising a housing extending along a reference axis, within which extends at least one shaft also extending along the reference axis. This shaft is generally driven in rotation by means of a motor to rotate around the reference axis, so that the joint provides a pivot joint function.

[0005] When the robotic arm is assembled, the actuator housing is typically attached to the proximal segment of the robotic arm via a mounting unit, on one side of the actuator, and the actuator shaft is typically attached to the distal segment of the robotic arm via another mounting unit, on a second side of the actuator, axially opposite to the first side.

[0006] Depending on the mass of the element attached to the actuator shaft, the latter can be subjected to significant bending stresses, leading to elastic deformation of the shaft. The deflection induced by such a load on the shaft can cause various disturbances in the actuator's nominal kinematics, degrading its performance and weakening the assembly.

[0007] The invention aims to overcome all or part of the drawbacks of the prior art, by proposing an actuator with a more robust architecture while having a reduced footprint. PRESENTATION OF THE INVENTION

[0008] More specifically, the invention relates to an actuator for a robotic arm configured to form an articulation of said robotic arm, the actuator comprising: a housing extending along a reference axis between a first open end and a second end delimiting a bottom of the housing; an output shaft extending in the housing between a first end and a second end, the first end of the output shaft being located on the same first side of the actuator as the first end of the housing; a motor housed in the housing and comprising a motor shaft extending in the housing between a first end and a second end, the motor shaft being configured to rotate around the reference axis of the housing, one of the ends of the motor shaft being located on the same second side of the actuator as the second end of the housing, opposite the bottom of the housing;a reducer configured to couple the second end of the motor shaft and the second end of the output shaft; a torque sensor configured to measure a torque applied to the output shaft.

[0009] The said actuator is remarkable in that the output shaft and the housing are each secured to the robotic arm by a fastening unit, the fastening units being located on the first side of the actuator.

[0010] Thanks to this combination of features, the distance between the two mounting units is significantly reduced, thereby substantially reducing the lever arm of a bending moment generated by a load attached to the output shaft. This, in turn, reduces the elastic deformation of the output shaft, particularly its deflection. Furthermore, this design protects the actuator motor, which is thus axially recessed relative to the mounting units. In addition, this design allows for increased compactness of the drivetrain components, notably enabling the integration of a torque sensor.

[0011] Furthermore, the housing comprises a first housing body with a second end defining the housing base, the drive shaft extending axially within the first housing body, and a second housing body with a first end protruding from the housing, the output shaft extending axially within the second body, the first and second housing bodies being rigidly connected. In this configuration, the housing can be easily disassembled, particularly for maintenance purposes.

[0012] Advantageously, the sensor extends axially between the first end of the output shaft and the second end of the output shaft. Furthermore, the torque sensor is advantageously positioned radially relative to the output shaft, allowing for a direct reading of the torque received by the output shaft.

[0013] Advantageously, the drive shaft and the output shaft are coaxial.

[0014] Advantageously, the first end of the housing and the first end of the output shaft extend in the same plane orthogonal to the housing's reference axis. In such a configuration, the output shaft is completely protected by the housing.

[0015] Advantageously, the mounting unit securing the output shaft to the robotic arm and the mounting unit securing the housing to the robotic arm are located in the plane orthogonal to the housing's reference axis. In such a configuration, the axial distance between the two mounting units is zero, so the lever arm of a bending moment generated by a load attached to the output shaft is minimized.

[0016] Advantageously, the torque sensor includes a strain gauge attached to the output shaft and a detector attached to the housing, the detector being configured to detect a deformation of the strain gauge.

[0017] Advantageously, the motor is an electric motor comprising a stator attached to the casing and a rotor attached to the motor shaft.

[0018] Advantageously, the housing includes a third body forming a cover, the cover extending radially around the first end of the output shaft.

[0019] According to another aspect of the invention, it relates to a comprising: a proximal segment; a distal segment; an actuator as described above, the housing being secured to the proximal segment by one of the fastening units and the output shaft being secured to the proximal segment by the other fastening unit.

[0020] According to another aspect of the invention, it relates to a robot, in particular a humanoid robot, comprising at least one robotic arm such as the one described above. PRESENTATION OF THE FIGURES

[0021] 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:

[0022] This is a schematic representation of a robotic arm according to a first aspect of the invention;

[0023] This is a schematic cross-sectional representation of an actuator of the robotic arm according to another aspect of the invention.

[0024] 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

[0025] The invention relates, according to a first aspect, to a robot (not illustrated), in particular a humanoid robot. According to another aspect of the invention, the robot comprises a robotic arm 1 as illustrated in the figure, including in particular a proximal segment 3 and a distal segment 5.

[0026] According to another aspect of the invention, the robotic arm 1 comprises an actuator 2 configured to form a joint of the robotic arm 1. In the case where the robotic arm 1 is the arm of a humanoid robot, such a joint 2 is, in particular, comparable to a human elbow or wrist. In such a configuration, the proximal segment 3 can form a robot arm (anatomically comparable to the human humerus) or a robot forearm, and the distal segment can form a robot forearm or hand, respectively, or alternatively, a gripper.

[0027] This is a schematic cross-sectional view illustrating the robotic arm 1 and, more specifically, the actuator 2. The actuator 2 includes a housing 4 extending along a reference axis 100, between a first open end and a second end defining the bottom of the housing. The housing 4 has a generally cylindrical shape. This housing 4 protects the electromechanical components of the actuator 2.

[0028] The actuator 2 also includes an output shaft 6 extending within the housing 4 between a first end and a second end, along the reference axis 100. The first end of the output shaft 6 is located on the same first side of the actuator 2 as the first end of the housing, i.e., the open end. The output shaft 6 is configured to drive an external load.

[0029] Advantageously, the first end of the housing 4 and the first end of the output shaft 6 extend in the same plane 200, orthogonal to the reference axis 100 of the housing 4. In such a configuration, the output shaft 6 is completely protected by the housing 4.

[0030] The actuator 2 also includes a motor 8 housed in the casing 4. The actuator 2 also includes a drive shaft 10 extending within the casing 4 between a first end and a second end. The motor 8 is configured to drive the drive shaft 10 in rotation.

[0031] The drive shaft 10 is configured to rotate around the reference axis 100 of the housing 4, and thus extends along said reference axis 100. One end of the drive shaft 10 is located on the same second side of the actuator 2 as the second end of the housing 4, opposite the bottom of the housing.

[0032] Preferably, motor 8 is an electric motor comprising a stator fixed to the casing and a rotor fixed to the motor shaft.

[0033] To closely mimic the articulation of a human elbow, the drive shaft 10 and the output shaft 6 are preferably coaxial. In other words, in this configuration, the output shaft 6 is also configured to pivot around the reference axis 100 of the housing 4.

[0034] Advantageously, the housing includes a first body 4b of housing 4 comprising the second end of the housing 4, that is to say the end delimiting the bottom of the housing 4. The drive shaft 10 then extends axially in the first body 4b of housing 4.

[0035] Similarly, the housing 4 comprises a second body 4c, which includes the first open end of the housing 4. The output shaft 6 extends axially within the second body 4c. The first body 4b and the second body 4c are mechanically joined. Such a housing 4, consisting of two bodies 4b and 4c, has the advantage of being easily disassembled for maintenance.

[0036] Alternatively, crankcase 4 is a single piece.

[0037] The actuator 2 also includes a reducer 12 configured to couple the second end of the motor shaft 10 and the second end of the output shaft 6. The reducer 12 is, for example, formed by an epicyclic gear train, or preferably by a strain-wave gear, commonly referred to as a "Harmonic drive" by those skilled in the art.

[0038] The output shaft 6 and the housing 4 are attached to the robotic arm 1, each by a fastening unit 16. The fastening units 16 are located on the first side of the actuator 2. By the term "attached", it is understood in particular that the output shaft 6 and the housing 4 are mechanically connected, by means of the fastening units 16, to different parts constituting the robotic arm 1.

[0039] The actuator 2 includes a torque sensor 14 configured to measure a torque applied to the output shaft 6. Preferably, the torque sensor 14 includes a strain gauge attached to the output shaft 6 and a detector attached to the housing, the detector being configured to detect a deformation of the strain gauge.

[0040] Thanks to this combination of features, the distance between the two mounting units 16 is significantly reduced, thereby substantially reducing the lever arm of a bending moment generated by a load attached to the output shaft 6. This, in turn, reduces the elastic deformation of the output shaft 6, particularly its deflection. Furthermore, this design protects the actuator motor, which is thus set back axially from the mounting units. In addition, this design allows for increased compactness of the drivetrain components, notably enabling the integration of a torque sensor.

[0041] The 16 fixing units illustrated on the diagram are notably formed by screws but can be formed by any fixing element, in particular removable.

[0042] Here, the output shaft 6 is subjected to the distal segment 5 and the housing 4 is subjected to the proximal segment 3. An inverse configuration, in which the output shaft 6 is subjected to the proximal segment 3 and the housing 4 is subjected to the distal segment 5, is also possible.

[0043] In the case where the robotic arm 1 forms the arm of a humanoid robot comprising a body, the robotic arm 1 is mounted on said robot body so that the first side of the actuator 2 is further away from the robot body than the second side of the actuator 2. Thus, the actuator is more protected by the segments 3,5 of the robotic arm and by the robot body.

[0044] In the case where the first end of the housing 4 and the first end of the output shaft 6 are coplanar, it can advantageously be provided that the fixing unit 16 securing the output shaft 6 to the robotic arm 1 and the fixing unit 16 securing the housing 4 to the robotic arm 1 are also located in this same plane 200. In such a configuration, an axial distance between the two fixing units 16 is substantially zero, so that the lever arm of a bending moment generated by a load attached to the output shaft 6 is minimized.

[0045] Advantageously, the housing 4 includes a third body forming a cover 4a. This cover 4a extends radially around the first end of the output shaft, thus limiting the exposure of the mechanical components to the external environment. When the housing 4 includes such a cover, said cover 4a can be secured to the second body 4b by means of the fastening units 16 that attach the housing 4 to the robotic arm. This improves the mechanical strength of the assembly, and this design reduces the number of fastening elements required to hold the cover 4a in position.

[0046] Advantageously, the torque sensor 14 is positioned radially opposite the output shaft 6, allowing a direct reading of the torque received by the output shaft 6. Furthermore, the torque sensor 14 can preferably be housed between two shoulders of the housing 4. One of the two shoulders is advantageously formed by the first open end of the housing 4. Thus, the attachment of the housing 4 to the robotic arm 1 by the fastening units 16 is located on the first shoulder of the housing 4. A second of the two shoulders is advantageously positioned radially opposite the second end of the output shaft.

[0047] Furthermore, as illustrated in the figure, the actuator 2 can include two bearings 18, for example, ball bearings. Here, an inner ring of one of the bearings 18 is fixed to the drive shaft 10 and an outer ring fixed to the housing 4. Similarly, an inner ring of one of the bearings 18 is fixed to the output shaft 6 and an outer ring fixed to the housing 4. In such a configuration, the rotational guidance of the two shafts 6, 10 around the reference axis 100 is improved.

Claims

Actuator (2) for a robotic arm (1) configured to form a joint of said robotic arm (1), the actuator (2) comprising: a housing (4) extending along a reference axis (100) between a first open end and a second end defining a bottom of the housing (4); an output shaft (6) extending in the housing (4) between a first end and a second end, the first end of the output shaft (6) being located on the same first side of the actuator (2) as the first end of the housing (4); a motor housed in the housing (4) and comprising a motor shaft (10) extending in the housing (4) between a first end and a second end, the motor shaft (10) being configured to rotate about the reference axis (100) of the housing (4), one end of the motor shaft (10) being located on the same second side of the actuator (2) that the second end of the casing (4), opposite the bottom of the casing (4);a reducer (12) configured to couple the second end of the drive shaft (10) and the second end of the output shaft (6); a torque sensor (14) configured to measure a torque applied to the output shaft (6); the output shaft (6) and the housing (4) being secured to the robotic arm (1) each by a mounting unit (16), the mounting units (16) being located on the first side of the actuator (2); the housing (4) comprising a first housing body (4b) comprising the second end defining the bottom of the housing (4), the drive shaft (10) extending axially into the first housing body (4), and a second housing body (4c) comprising the first end opening, the output shaft (6) extending axially into the second body (4c), the first housing body (4b) and the second housing body (4c) of casing (4) being integral.; Actuator (2) according to claim 1, wherein the sensor extends axially between the first end of the output shaft (6) and the second end of the output shaft (6). Actuator (2) according to any one of the preceding claims, wherein the drive shaft (10) and the output shaft (6) are coaxial. Actuator (2) according to any one of the preceding claims, wherein the first end of the housing (4) and the first end of the output shaft (6) extend in the same plane (200) orthogonal to the reference axis (100) of the housing (4). Actuator (2) according to claim 3, wherein the fixing unit (16) securing the output shaft (6) to the robotic arm (1) and the fixing unit (16) securing the housing (4) to the robotic arm (1) are located in the plane (200) orthogonal to the reference axis (100) of the housing (4). Actuator (2) according to any one of the preceding claims, wherein the torque sensor (14) comprises a strain gauge integral with the output shaft (6) and a detector integral with the housing (4), the detector being configured to detect a deformation of the strain gauge. Actuator (2) according to any one of the preceding claims, wherein the motor is an electric motor comprising a stator integral with the housing (4) and a rotor integral with the motor shaft (10). Robotic arm (1) of a robot, in particular humanoid, comprising: a proximal segment (3); a distal segment (5); an actuator (2) according to any one of the preceding claims, the housing (4) being attached to the proximal segment (3) by one of the fixing units (16) and the output shaft (6) being attached to the proximal segment (3) by the other fixing unit (16). Robot, in particular humanoid, comprising at least one robotic arm (1) according to claim 8.

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