Actuator for a robotic arm with improved configuration

Abstract

The present invention relates to an actuator (10) for a robotic arm, which includes: - an inlet casing (12); - an outlet casing (15); - an electric motor (18) including a stator (19) and a rotor (20); - a mechanical speed reducer (23); - a hollow output shaft (25) being arranged inside the hollow rotor shaft (21), so that the hollow output shaft (25) and the hollow rotor shaft (21) are coaxial with respect to each other; - the hollow output shaft (25) being rotatably connected at a first end to the output casing (15) bearing a circuit board (26) and rotatably connected to a second end to an element (271) of a rotary connector (29); and - at least one electric wire (32) which is arranged inside a hollow space passing through the hollow output shaft (15).

Description

DESCRIPTION TITLE: ACTUATOR FOR A ROBOTIC ARM WITH IMPROVED CONFIGURATION

[0001] The present invention relates to an actuator for a robotic arm with an improved configuration. The invention finds a particularly advantageous application in the field of robotics, in particular with remotely controlled robotic arms used for welding applications.

[0002] In a manner known per se, a robotic arm comprises a plurality of segments consisting of non-articulated solid bodies connected to each other by actuators conferring a degree of freedom in rotation of one segment relative to another. All of the actuators allow the robotic arm to move in rotation and / or translation along at least one axis, in particular three axes, of an orthonormal reference frame. For this purpose, the actuator conventionally comprises an electric motor associated with a mechanical speed reducer, an angular position measurement sensor making it possible to measure an angular position of a segment relative to another segment and, where appropriate, in particular for collaborative robots, a torque sensor making it possible to measure a torque applied to the actuator.

[0003] Current actuators located at one end of an arm segment have a high mass and are connected in series with each other, which generates a high inertia and implies an exponential increase in the force required to actuate the robotic arm. Typically, a torque / mass ratio of a robotic arm actuator is between 8 and 15 Nm / kg.

[0004] Additionally, the rotation of an actuator is typically angularly limited by a stop integrated into the actuator while some applications, particularly in the field of remote-controlled welding, may require a segment of the arm to travel more than 360 degrees when controlling the arm.

[0005] The invention aims to effectively meet this need by proposing an actuator for a robotic arm comprising: - an input casing provided with a fixing interface capable of ensuring fixing of the input casing with a first segment of the robotic arm, - an output casing provided with a fixing interface capable of ensuring fixing of the output casing with a second segment of the robotic arm, - an electric motor comprising a stator fixed to the input housing and a rotor mounted on a hollow rotor shaft, - a mechanical speed reducer having an input and an output, the hollow rotor shaft being connected to the input of the mechanical speed reducer and the output housing being connected to the output of the mechanical speed reducer, - a hollow output shaft being arranged inside the hollow rotor shaft, such that the hollow output shaft and the hollow rotor shaft are coaxial with each other, - the hollow output shaft being rotationally connected at a first end to the output casing carrying an electronic card and rotationally connected at a second end to an element of a rotating connector, and at least one electrical wire being arranged inside a hollow space passing through the hollow output shaft.

[0006] The invention thus makes it possible, thanks to the configuration of the double hollow shaft actuator, to lighten and reduce the size of the actuator while having a high torque. It is thus possible to obtain a torque / mass ratio of the actuator according to the invention of between 40 and 80 Nm / kg. The fact of being able to produce a lightweight robotic arm also makes it possible to save electrical energy. The invention also makes it possible to eliminate axis stops to allow multi-turn rotation of one of the segments relative to the other segment of the robotic arm. The invention facilitates the control of a robotic arm, in particular during a welding operation.

[0007] According to one embodiment of the invention, at least one bearing is interposed radially between an external periphery of the hollow output shaft and an internal periphery of the hollow rotor shaft.

[0008] According to one embodiment of the invention, if two end planes of the stator are considered perpendicular to an axis of the actuator, the bearing is arranged between the two end planes or at one end of the stator so that one end plane intersects the bearing.

[0009] According to one embodiment of the invention, there is an axial overlap along an axis of the actuator between the stator of the electric motor, the input casing, and the output casing.

[0010] According to one embodiment of the invention, the element of the rotating connector is fixed on a slidingly mounted guide stud while being rotationally linked relative to the hollow output shaft.

[0011] According to one embodiment of the invention, said actuator comprises an elastic member bearing on the one hand on a washer carried by the guide stud and on the other hand on the element of the rotating connector so as to urge brushes against corresponding tracks of the rotating connector.

[0012] According to one embodiment of the invention, the hollow output shaft comprises longitudinal extension arms each provided with at least one portion inserted inside a groove of corresponding shape made in the guide stud.

[0013] According to one embodiment of the invention, a screw inserted inside a through opening made in the element of the rotating connector cooperates with a tapped hole made in the guide stud.

[0014] According to one embodiment of the invention, said actuator comprises at least one current-breaking brake having an unlocked state when said current-breaking brake is supplied with a current and a locked state when said current-breaking brake is no longer supplied with a current.

[0015] According to one embodiment of the invention, according to a first safety level of the current-breaking brake, the rotating connector comprises at least one safety track intended to cooperate with a corresponding brush, so that a break in contact between the safety track and the corresponding brush causes a reaction from a speed variator capable of cutting off a power supply to the current-breaking brake to apply it.

[0016] According to one embodiment of the invention, according to a second safety level of the current-failure brake, a cut-off of an electrical power supply to the speed variator is capable of causing a cut-off of a power supply to the current-failure brake, causing its activation.

[0017] According to one embodiment of the invention, the safety track is a circular track located on the outside of the rotating connector. The outer track is the first track to wear, so that the actuator will be safe before a potential malfunction occurs due to transmission errors of control signals passing on less worn inner tracks.

[0018] According to one embodiment of the invention, the hollow output shaft is made of steel and the output housing is made of aluminum.

[0019] According to one embodiment of the invention, the hollow output shaft is mounted glued inside a receiving housing made in the output casing.

[0020] The invention further relates to a robotic arm comprising a plurality of actuators as previously defined comprising hollow output shafts, and a plurality of segments extending between two consecutive actuators.

[0021] According to one embodiment of the invention, all the actuators are powered by a single standby battery allowing a corresponding encoder of an actuator to retain its position in memory when said actuator is powered off.

[0022] According to one embodiment of the invention, electrical wires connected to the single standby battery pass inside the hollow output shafts.

[0023] The present invention will be better understood and other characteristics and advantages will become apparent upon reading the detailed description which follows, comprising embodiments given for illustrative purposes with reference to the appended figures, presented as non-limiting examples, which may be used to complete the understanding of the present invention and the description of its implementation and, where appropriate, contribute to its definition, on which:

[0024] [Fig. 1] Figure 1 is a perspective view of a robotic arm actuator according to the present invention;

[0025] [Fig. 2] [Fig. 3] Figures 2 and 3 are perspective and longitudinal sectional views from two different viewing angles of the robotic arm actuator according to the present invention;

[0026] [Fig. 4] Figure 4 shows a perspective and longitudinal sectional view of the rear part of the hollow output shaft on which a rotating collector of the actuator according to the invention is mounted;

[0027] [Fig. 5] Figure 5 is a detailed perspective view of the mechanical connection between the hollow output shaft and a guide stud on which is mounted an element of the rotating connector of the actuator according to the invention;

[0028] [Fig. 6] Figure 6 is a perspective view in which a partial section has been made of the rotating collector, the guide stud and the hollow output shaft of the actuator according to the invention;

[0029] [Fig. 7] Figure 7 is a detailed perspective view of a device for taking up play in the rotating collector of the actuator according to the invention;

[0030] [Fig. 8] Figure 8 is a front view of tracks of the rotating collector comprising safety tracks and communication tracks of the actuator according to the invention.

[0031] It should be noted that, in the figures, the structural and / or functional elements common to the different embodiments may have the same references. Thus, unless otherwise stated, such elements have identical structural, dimensional and material properties.

[0032] Figures 1, 2 and 3 show an X-axis actuator 10 for a robotic arm comprising an input housing 12 provided with a fixing interface 13 capable of ensuring fixing of the input housing 12 with a first segment of the robotic arm. The input casing 12 has an annular shape extending axially relative to the X axis. The projecting fixing interfaces 13 comprise fixing holes for the passage of fixing members, such as screws or studs or any other fixing member suitable for the application. Preferably, the input casing 12 is made of aluminum in order to lighten the actuator 10. However, as a variant, the input casing 12 may be made of another metallic material suitable for the application, in particular steel, or of a plastic material or of a composite material.

[0033] Furthermore, an output casing 15 is provided with a fixing interface 16 capable of ensuring fixing of the output casing 15 with a second segment of the robotic arm. The output casing 15 comprises an annular wall of axial orientation relative to the X axis and an annular wall of radial orientation relative to the X axis carrying an electronic card 26. The fixing interfaces 16 comprise fixing holes for the passage of fixing members, such as screws or studs or any other fixing member suitable for the application. Preferably, the output casing 15 is made of aluminum in order to lighten the actuator 10. However, as a variant, the output casing 15 can be made of another metallic material suitable for the application, in particular steel, or of a plastic material or of a composite material. The input housing 12 and the output housing 15 are coaxial with respect to the X axis of the actuator.

[0034] An electric motor 18 comprises a stator 19 fixed to the input housing 12 and a rotor 20 mounted on a hollow rotor shaft 21. The stator 19 is preferably a wound stator and the rotor 20 is preferably a permanent magnet rotor. The electric motor 18 is preferably a brushless motor (called "brushless" according to English terminology) capable of being controlled by a speed variator comprising an inverter, in particular a transistor inverter.

[0035] In order to determine an angular position of the rotor 20, the electric motor 18 is associated with an encoder 22 comprising a magnetic annular target integral in rotation with the hollow rotor shaft 21, and at least one fixed magnetic field sensor, in particular a Hall effect type sensor arranged close to the target. Under the effect of the rotation of the target together with the shaft of hollow rotor 21, the magnetic field received by the sensor varies. The sensor is connected to an electronic management and control device, and transmits to it signals depending on the magnetic fields received, this device processing said signals to deduce the angular position as well as the speed of the rotor 20.

[0036] A mechanical speed reducer 23 has an input and an output. The hollow rotor shaft 21 is connected to the input of the mechanical speed reducer 23 and the output housing 15 is connected to the output of the mechanical speed reducer 23. Preferably, the mechanical speed reducer 23 is of the harmonic type. Such a reducer has the advantage of being able to be easily integrated into the actuator 10. Alternatively, it is possible to use a conventional gear wheel speed reducer or any other type of speed reducer suitable for the application.

[0037] A hollow output shaft 25 is arranged inside the hollow rotor shaft 21, such that the hollow output shaft 25 and the hollow rotor shaft 21 are coaxial with each other with respect to the X axis.

[0038] The hollow output shaft 25 comprises a recess passing axially through the shaft from one side to the other. The wall of the shaft 25 may also comprise a window at one end for the passage of at least one electrical wire, in particular several electrical wires arranged in one or more bundles of electrical wires.

[0039] The hollow output shaft 25 is rotatably connected at a first end to the output casing 15 carrying the electronic card 26 and rotatably connected at a second end to an element 27.1 of a rotating connector 29. The hollow output shaft 25 is preferably mounted glued inside a receiving housing made in the output casing 15. The mounting can be carried out by cold gluing, in particular by means of a single-component glue or any other type of glue suitable for the application. Alternatively, the hollow output shaft 25 is mounted shrink-fitted or force-fitted with the output casing 15.

[0040] Preferably, the hollow output shaft 25 is made of steel in order to have sufficient rigidity to withstand the torques imposed on the actuator 10. Alternatively, the hollow output shaft 25 may be made of another material. metallic, in particular steel, or in a plastic material or in a composite material.

[0041] At least one electrical wire 32 is arranged inside a hollow space passing through the hollow output shaft 15. The electrical wire 32 can provide at least one electrical connection between the electronic card 26 and the rotating connector 29. As a variant, the electrical wire 32 can provide an electrical connection between other electrical members of the actuator 10 or between electrical members external to the actuator 10 which may in particular belong to other actuators or to a control unit of a robotic arm.

[0042] The rotating connector 29 comprises a first element 27.1 and a second rotating element 27.2 which are movable in rotation relative to each other. One of the elements 27.1, 27.2 carries brushes 28 intended to cooperate with circular electrical tracks 43 carried by the other element 27.1, 27.2 (see figure 8). In the example shown, the first element 27.1 carrying the brushes 28 is mounted on the hollow output shaft 25. Alternatively, the structure can be reversed and the second element 27.2 carrying the electrical tracks 43 can be mounted on the hollow output shaft 25. The circular electrical tracks 43 and the brushes 28 have contact faces extending in a radial plane relative to the axis X, so that the contact faces of the brushes 28 can establish electrical contact, in an axial direction relative to the axis X, with the contact faces of the brushes 28.

[0043] As can be seen in Figure 3, at least one bearing 35, in this case two bearings 35 are interposed radially between an outer periphery of the hollow output shaft 15 and an inner periphery of the hollow rotor shaft 21. If we consider two end planes P1, P2 of the stator 19 perpendicular to an axis X of the actuator 10, a given bearing 35 is arranged between the two end planes P1, P2 or at one end of the stator 19) so that an end plane P1, P2 intersects the bearing 35.

[0044] There is also an axial overlap along an X axis of the actuator between the stator 19 of the electric motor 18, the input casing 12, and the output casing 15. Such a configuration makes it possible to obtain a compact assembly that can be easily integrated inside a robotic arm.

[0045] As can be clearly seen in Figures 4, 5, 6, and 7, the element 27.1 of the rotating connector 29 is fixed on a guide stud 38 mounted to slide axially, relative to the axis X, while being linked in rotation relative to the hollow output shaft 25.

[0046] An elastic member 41 bears on the one hand on a washer 42 carried by the guide stud 38 and on the other hand on the element 27.1 of the rotating connector 29 so as to axially urge the brushes 28 against the corresponding tracks 43 of the rotating connector 29. The elastic member 41 is preferably a flat spiral spring. Alternatively, the elastic member 41 may be a helical spring, a conical spring, an elastic washer, a leaf washer, a leaf spring or any other elastic member suitable for the application. Such a configuration makes it possible to compensate for the wear of the brushes 28 by guaranteeing electrical contact between the brushes 28 and the electrical tracks 43 despite the wear of the brushes 28.

[0047] The hollow output shaft 25 comprises arms 44 extending longitudinally relative to the axis X, each provided with at least one portion inserted inside a groove 47 of corresponding shape made in the guide stud 38, as shown in FIGS. 5 and 7. The groove 47 elongated along the axis X makes it possible to confer a degree of freedom in translation of the guide stud 38 relative to the hollow output shaft 25 while ensuring a rotational connection between these two elements 25 and 38.

[0048] Furthermore, as can be seen in particular in Figures 4 and 6, a screw 48 inserted inside a through opening made in the element 27.1 of the rotating connector 29 cooperates with a tapped hole made in the guide stud 38. This makes it possible to connect the element 27.1 in rotation with the guide stud 38.

[0049] The actuator 10 further comprises at least one current-breaking brake 51 visible in FIGS. 2 and 3 having an unlocked state when said current-breaking brake 51 is supplied with a current and a locked state when said current-breaking brake 51 is no longer supplied with a current.

[0050] According to a first safety level of the current-breaking brake 51, the rotating connector 29 comprises at least one safety track 43' illustrated in FIG. 8 intended to cooperate with a corresponding brush 28, so that a break in contact between the safety track 43' and the corresponding brush 28 causes a reaction from a speed variator capable of cutting off the power supply to the current-breaking brake 51 to apply it.

[0051] According to a second level of safety of the current-breaking brake 51, a cut-off of an electrical power supply to the speed variator is capable of causing a cut-off of a power supply to the current-breaking brake 51, causing its activation.

[0052] As illustrated in Figure 8, two safety tracks 43' are circular tracks located outside the rotating connector 29, in particular the element 27.1. Circular communication tracks 43 on which communication signals pass correspond to the internal tracks of the rotating connector 29. In other words, the safety tracks 43' are arranged outside around the communication tracks 43.

[0053] The outer track(s) 43' are the first tracks to wear, so that the actuator 10 will be safe before a potential malfunction occurs due to transmission errors of control signals passing on less worn inner tracks 43.

[0054] Since the outer tracks are the first to wear, such a configuration makes it possible to avoid a situation in which the main communication with the actuator 10 would be degraded while the safety tracks 43' continue to allow rotation of the actuator 10.

[0055] The invention also relates to a robotic arm comprising a plurality of actuators 10 comprising hollow output shafts 15, and a plurality of segments extending between two consecutive actuators 10.

[0056] Preferably, all the actuators 10 are powered by a single standby battery allowing the corresponding encoder 22 of an actuator 10 to retain its position in memory when said actuator 10 is powered off. Electrical wires connected to the single standby battery pass inside the hollow output shafts 15.

[0057] Of course, the various features, variants and / or embodiments of the present invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

[0058] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms and other variations that may be envisaged by those skilled in the art within the scope of the present invention and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination.

Claims

CLAIMS 1. Actuator (10) for a robotic arm, said actuator (10) having an axis (X) characterized in that said actuator (10) comprises: - an input casing (12) provided with a fixing interface (13) capable of ensuring fixing of the input casing (12) with a first segment of the robotic arm, - an output casing (15) provided with a fixing interface (16) capable of ensuring fixing of the output casing (15) with a second segment of the robotic arm, - an electric motor (18) comprising a stator (19) fixed on the input casing (12) and a rotor (20) mounted on a hollow rotor shaft (21), - a mechanical speed reducer (23) having an input and an output, the hollow rotor shaft (21) being connected to the input of the mechanical speed reducer (23) and the output housing (15) being connected to the output of the mechanical speed reducer (23), - a hollow output shaft (25) being arranged inside the hollow rotor shaft (21), such that the hollow output shaft (25) and the hollow rotor shaft (21) are coaxial with each other, - the hollow output shaft (25) being rotationally connected at a first end to the output casing (15) carrying an electronic card (26) and rotationally connected at a second end to an element (27.1) of a rotating connector (29), and - at least one electric wire (32) being arranged inside a hollow space passing through the hollow output shaft (15), - the element (27.1) of the rotating connector (29) being fixed on a guide stud (38) mounted to slide relative to the axis (X) of the actuator (10) while being linked in rotation relative to the hollow output shaft (25), - said actuator (10) further comprises an elastic member (41) bearing on the one hand on a washer (42) carried by the guide stud (38) and on the other hand on the element (27.1) of the rotating connector (29) so as to urge brushes (28) against corresponding tracks (43) of the rotating connector (29).

2. Actuator according to claim 1, characterized in that at least one bearing (35) is interposed radially between an external periphery of the hollow output shaft (15) and an internal periphery of the hollow rotor shaft (21).

3. Actuator according to claim 1 or 2, characterized in that if two end planes (P1, P2) of the stator (19) are considered perpendicular to an axis (X) of the actuator (10), the bearing (35) is arranged between the two end planes (P1, P2) or at one end of the stator (19) so that one end plane (P1, P2) intersects the bearing (35).

4. Actuator according to any one of claims 1 to 3, characterized in that there is an axial overlap along an axis of the actuator between the stator (19) of the electric motor (18), the input casing (12), and the output casing (15).

5. Actuator according to any one of claims 1 to 4, characterized in that the hollow output shaft (25) comprises longitudinal extension arms (44) each provided with at least one portion inserted inside a groove (47) of corresponding shape made in the guide stud (38).

6. Actuator according to any one of claims 1 to 5, characterized in that a screw (48) inserted inside a through opening made in the element (27.1) of the rotating connector (29) cooperates with a tapped hole made in the guide stud (38).

7. Actuator according to any one of claims 1 to 6, characterized in that it comprises at least one current-breaking brake (51) having an unlocked state when said current-breaking brake (51) is supplied with a current and a locked state when said current-breaking brake (51) is no longer supplied with a current.

8. Actuator according to claim 7, characterized in that, according to a first safety level of the current-breaking brake (51), the rotating connector (29) comprises at least one safety track (43') intended to cooperate with a corresponding brush (28), so that a break in contact between the track safety (43') and the corresponding brush (28) causes a reaction from a speed variator capable of cutting off a power supply to the current-breaking brake (51) to apply it.

9. Actuator according to claim 8, characterized in that, according to a second safety level of the current-failure brake (51), a cut-off of an electrical power supply to the speed variator is capable of causing a cut-off of a power supply to the current-failure brake (51) causing its activation.

10. Actuator according to claim 8 or 9, characterized in that the safety track (43') is a circular track located outside the rotating connector (29).

11. Actuator according to any one of claims 1 to 10, characterized in that the hollow output shaft (25) is made of steel and the output casing (15) is made of aluminum.

12. Actuator according to any one of claims 1 to 11, characterized in that the hollow output shaft (25) is mounted glued inside a receiving housing made in the output casing (15).

13. Robotic arm comprising a plurality of actuators (10) as defined according to any one of the preceding claims comprising hollow output shafts (15), and a plurality of segments extending between two consecutive actuators (10).

14. Robotic arm according to claim 13, characterized in that all the actuators (10) are powered by a single standby battery allowing a corresponding encoder (22) of an actuator (10) to keep its position in memory when said actuator (10) is powered off.

15. Robotic arm according to claim 14, characterized in that electrical wires connected to the single standby battery pass inside the hollow output shafts (15).

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