Actuator for robotic arm

Abstract

The invention relates to an actuator for a robotic arm (110), comprising: - a tubular casing; - an output shaft extending in the tubular casing; - a motor mounted in the tubular casing; - an input connection located outside the tubular casing; and - an output connection that is located in the tubular casing and is connected to the input connection by electrical connection means, the connection means comprising a rotating slip ring, and the output shaft is hollow.

Description

Actuator for robotic arm

[0001] The field of the invention is that of the design and manufacture of cobotic systems.

[0002] More specifically, the invention relates in particular, but not exclusively, to an actuator for a robotic arm.

[0003] Robotic arms can be used for a variety of tasks.

[0004] One of these tasks is assisting people with disabilities.

[0005] Indeed, certain disabilities reduce people's ability to use their arms to grasp and move objects.

[0006] Cobots, a term used to describe robotic limbs designed to interact with a user, are used to enable disabled people to regain autonomy in their movements.

[0007] For example, robotic arms can be mounted on wheelchairs to allow users to grasp and manipulate objects when their own arms are unable to do so.

[0008] The patent document published under number EP2355958 describes a robotic arm adaptable to a wheelchair.

[0009] Known robotic arms have a plurality of sections articulated relative to each other.

[0010] The joints are formed in particular by actuators.

[0011] Conventionally, an actuator comprises a motor associated with a reducer.

[0012] The motor allows two sections to be moved relative to each other and the reducer allows the torque supplied by the motor to be increased to increase the strength of the robotic arm.

[0013] However, the actuators used have many flaws.

[0014] First, they are limited in their degrees of freedom.

[0015] In other words, when multiple actuators are mounted in the robotic arm, they are positioned in series from a first end of the arm to a second end.

[0016] The cables intended to supply power and instructions to the actuators must therefore pass through the robotic arm.

[0017] Also, to avoid the risk of twisting and tangling of the cables, the rotation of the joints is limited.

[0018] This then complicates programming since it is necessary to ensure that certain sections are kept in a particular orientation when moving the robotic arm, while limiting the range of movement of the arm so as not to hinder people moving around the robotic arm.

[0019] For example, when the object grasped at the end of the robotic arm is an open glass or jar, it is necessary to keep the orientation of the glass or jar constant, or almost constant, to allow it to move without spilling its contents.

[0020] Depending on the starting position of the arm when it grasps the glass or jar, the movement can be complicated.

[0021] Second, when mounted on wheelchairs, robotic arms must have appropriate aesthetics and space requirements. In addition, robotic arms must also be lightweight and consume little electrical power to reduce the size of the wheelchair's battery(ies).

[0022] Therefore, the size of the joints constrains the power developed by the actuators.

[0023] Indeed, to increase the power of an actuator, without excessively increasing its cost, a widespread solution is to increase the size of the actuator, in particular the motor and / or the reducer.

[0024] However, increasing the size of actuators directly impacts the aesthetics and use of the robotic arm. Furthermore, the size of actuators also impacts the performance of the robotic arm.

[0025] At the expense of aesthetics and bulk, robotic arms are developed to provide the desired use.

[0026] Third, actuators require maintenance throughout their life.

[0027] This maintenance is particularly long, costly and tedious given the high number of parts contained in the actuators.

[0028] Indeed, in order to maximize the ratio between the power developed and the weight of the actuator, many wear parts, such as bearings, are used.

[0029] However, these wear parts, as their name suggests, wear out as the robotic arms are used. Maintenance is therefore necessary but problematic because, apart from the cost of the service, it requires the robotic arm to be immobilized for a long time.

[0030] The invention aims in particular to overcome the drawbacks of the prior art.

[0031] More specifically, the invention aims to propose an actuator for a robotic arm, the design of which makes it possible to limit its weight and size while increasing its developed power.

[0032] The invention also aims to provide such an actuator which makes it possible to produce joints offering a greater range of movement than those of the prior art.

[0033] The invention further aims to provide such an actuator which is reliable and whose maintenance is simplified compared to the actuators of the prior art.

[0034] These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to an actuator for a robotic arm comprising: a tubular casing extending along a main axis; an output shaft extending in the tubular casing along the main axis; a reducer coupled to the output shaft; a motor mounted in the tubular casing and comprising a stator secured to the tubular casing and a rotor coupled to the reducer; an input connection located outside the tubular casing, and an output connection located in the tubular casing and connected to the input connection by electrical connection means, characterized in that the connection means comprise a rotating collector, and in that the output shaft is hollow to allow the passage of cables joining the connection means to a device external to the actuator, and in that the actuator comprises means for guiding the rotation of the output shaft,interposed between the output shaft and the tubular casing, these guide means comprising a first member and a second member, the motor and the reducer being positioned between the first member and the second member, the tubular casing having three parts abutted along the main axis, including a central part, a first lateral part and a second lateral part, the central part being received between the first lateral part and the second lateral part, each lateral part comprising a shoulder for receiving the guide means, the first lateral part having a conical support extending and tapering towards the main axis, the shoulder of the first lateral part being made at a distal end of smaller diameter of the conical support.,

[0035] The use of a hollow output shaft combined with the presence of a rotating connector makes the actuator more compact than those of the prior art.

[0036] This also benefits the weight reduction of the actuator, which improves the power-to-weight ratio compared to prior art actuators.

[0037] In addition, the use of the hollow shaft and the rotating collector makes it possible to mount several actuators in series in a robotic arm while making it possible to rotate two parts of the arm over several turns relative to each other.

[0038] In fact, the risk of twisting the cables is eliminated by the fact that they pass through the output shaft. In addition, this reduces the limitation of movement of an arm equipped with actuators since the cables do not risk hindering the mobility of said arm.

[0039] The rotational guide means prevent bending of the output shaft, which could lead to damage to the actuator.

[0040] In addition, the guiding means make the actuator more reliable.

[0041] Thanks to the positioning of the motor and the reducer, the output shaft is guided near its ends, which further reduces the risk of bending.

[0042] The conical support limits the size of the first guide member, which further limits the weight of the actuator to the benefit of its size. This also benefits the aesthetics of the robotic arm, which can be more compact.

[0043] According to an advantageous aspect, the actuator also comprises a stress sensor configured to know, at any time, the forces applied to the output shaft.

[0044] This makes it possible, in particular, to monitor the activity of the actuator and to determine the stress of a joint in which the actuator is mounted.

[0045] According to another advantageous aspect, the stress sensor is mounted integrally with the tubular casing.

[0046] This allows easy access to the strain sensor for maintenance if necessary.

[0047] Furthermore, by being integral with the tubular casing, it is not subject to any movement which could be detrimental to data acquisition.

[0048] According to another advantageous aspect, the second plug is integral with the output shaft, the second member being interposed between the second plug and the second lateral part.

[0049] This also promotes the adaptability of the actuator as needed.

[0050] Indeed, for a specific need, it may be necessary to adapt the actuator. Changing the second cap allows this, quickly.

[0051] According to another advantageous aspect, at least one of the first member and the second member is a bearing.

[0052] The use of bearings allows efficient guidance with a small footprint.

[0053] According to another advantageous aspect, at least one of the first member and the second member is a plain bearing.

[0054] The use of a plain bearing further reduces the weight of the actuator.

[0055] According to another advantageous aspect, the rotating collector includes: a first part carrying at least three metal tracks, and a second part carrying at least three brushes each intended to cooperate with one of the metal tracks.

[0056] Two tracks can then be used for the transmission of a power current between several actuators connected in series, while the third track can allow the passage of a reference current allowing the actuator to be controlled.

[0057] The invention also relates to a robotic arm comprising at least two sections articulated relative to each other by means of

[0058] Compared to prior art robotic arms, a robotic arm according to the invention provides greater strength for less or at least the same weight.

[0059] Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment of the invention, given by way of illustrative and non-limiting example, and the appended drawings described below.

[0060] This is a schematic representation of a wheelchair carrying a robotic arm having at least one joint formed by an actuator according to the invention.

[0061] This is a schematic perspective representation of an actuator according to the invention.

[0062] This is a schematic representation in longitudinal section of an actuator according to the invention.

[0063] This is a simplified exploded schematic representation of an actuator according to the invention.

[0064] This is a schematic representation in longitudinal section of an exploded view of a tubular casing of the actuator according to the invention.

[0065] This is a schematic representation in longitudinal section of an electric rotating collector of the actuator according to the invention, this view showing a detail medallion on an enlarged scale.

[0066] Illustrates a wheelchair 100 provided with a robotic arm 110 comprising at least one actuator 1 according to the invention (illustrated by FIGS. 2 to 6). An actuator 1 according to the invention is notably used to form an articulation 120 of the robotic arm 110.

[0067] More specifically, the actuator 1 is used to form an articulation 120 between two sections of the robotic arm 110.

[0068] Illustrates an actuator 1 according to the invention.

[0069] The actuator 1 comprises: a tubular casing 2; an output shaft 3; a reducer 4 coupled to the output shaft 3; a motor 5; an input connector 6, and an output connector 7 located in the tubular casing 2 and connected to the input connector by electrical connection means.

[0070] As illustrated by the, the tubular casing extends along a main axis A.

[0071] Still with reference to the, the output shaft 3 is hollow and extends into the tubular casing 2 along the main axis A.

[0072] The fact that the output shaft 3 is hollow allows the passage of cables C joining the connection means to a device external to the actuator 1, as explained below.

[0073] The motor 5 is mounted in the tubular casing 2.

[0074] More precisely, the motor 5 comprises a stator 501 secured to the tubular casing 2 and a rotor 502 coupled to the reducer 4.

[0075] The coupling of the rotor 502 with the reducer 4 makes it possible to vary the rotation speed of the output shaft 3 relative to the rotation speed of the motor 5.

[0076] As seen in the, the stator 501 carries an electric coil 503 and the rotor 502 carries a plurality of magnets 504 intended to cooperate with a magnetic field generated by the coil 503 of the stator 501 in order to rotate the rotor 502.

[0077] With reference to the, the input connection 6 is located outside the tubular casing 2. On the other hand, the output connection 7 is located in the tubular casing 2. More precisely, the output connection 7 is located in the output shaft 3.

[0078] The connecting means comprise a rotating collector 8.

[0079] The use of a rotating collector 8 makes it possible to cancel, that is to say to avoid, the twisting of the cables C passing through the actuator 1, in particular for the series mounting of several actuators 1.

[0080] With reference to the, the rotating collector 8 includes: a first part 801 carrying at least three metal tracks 802, and a second part 803 carrying at least three brushes 804 intended to cooperate each with one of the metal tracks 802.

[0081] Two metal tracks 802 can in particular be dedicated to the passage of an electric supply current making it possible to supply several actuators 1 mounted in series.

[0082] A third of the metal tracks 802 can, for its part, be used for the passage of a control current for controlling the actuator 1.

[0083] Other metal tracks 802 may in particular be provided to allow the passage of control currents to other actuators 1.

[0084] As illustrated in Figures 3 and 4, the actuator 1 also comprises means for guiding the output shaft 3 in rotation.

[0085] These guide means are interposed between the output shaft 3 and the tubular casing 2.

[0086] More specifically, the rotational guide means comprise a first member 9 and a second member 10.

[0087] The first member 9 and the second member 10 are positioned such that the motor 5 and the reducer 4 are positioned between the first member 9 and the second member 10.

[0088] This benefits the compactness of the actuator 1, and the quality of rotational guidance of the output shaft 3.

[0089] According to one aspect, at least one of the first member 9 and the second member 10 is a bearing.

[0090] According to the embodiment illustrated by the, each of the first member 9 and the second member 10 is a bearing. The bearings may be ball bearings, needle bearings, tapered bearings, angular contact ball bearings, or any other type of bearing.

[0091] In a variant not shown in the figures, at least one of the first member 9 and the second member 10 is a plain bearing.

[0092] The rotational guide means may comprise other members 11, for example interposed between the output shaft 3 and the rotor 502.

[0093] With reference to figures 4 and 5, the tubular casing 2 has at least three parts abutted along the main axis A.

[0094] More specifically, the tubular casing 2 comprises a central part 201, a first lateral part 202 and a second lateral part 303.

[0095] The central portion 201 is received between the first lateral portion 202 and the second lateral portion 203.

[0096] Each lateral part 202, 203 comprises a shoulder 204 for receiving the guide means.

[0097] More specifically, as illustrated by the, the first lateral part 202 has a conical support 205 extending towards the inside of the tubular body 2, that is to say thinning in the direction of the main axis A, the shoulder 204 being made in said conical support 205. More precisely, the shoulder 204 of the first lateral part 202 is made at a distal end of smaller diameter of the conical support 205.

[0098] With reference to the exploded view of the, the tubular casing 2 is closed at a first end 206 by a first plug 207 and, at a second end 208, by a second plug 209.

[0099] The first plug 207 and the second plug 209 make it possible to seal the actuator 1 against any dust or dirt which could impair its proper functioning and lead to maintenance work, and therefore immobilization of the robotic arm 110 containing the faulty actuator 1.

[0100] To facilitate the assembly and maintenance of the actuator 1, the second cap 209 is secured to the output shaft 3.

[0101] The second member 10 is then interposed between the second plug 209 and the second lateral part 203 of the tubular casing 2, as illustrated by the.

[0102] According to the embodiment illustrated by the, the actuator 1 also comprises a stress sensor 11. The stress sensor 11 is mounted integral with the tubular casing 2 and is configured to know, at any time, the forces applied to the actuator 1 and in particular the forces applied to the output shaft 3.

[0103] The sensor 11 can also be connected to the rotating collector 8 to exchange data with a remote control unit.

[0104] As an illustrative and non-limiting example, the sensor 11 is a strain gauge.

[0105] In operation, the motor 5 rotates the output shaft 3.

[0106] The reducer 4 makes it possible to modify the torque supplied by the output shaft 3 according to the torque generated by the motor 5.

[0107] The transmission of information and power can be ensured between several actuators 1 mounted in series in a robotic arm 110, thanks to the presence of the rotating collector 8.

[0108] In fact, the cables maintain zero torsion since they pass through the output shaft 3 which is hollow.

[0109] Therefore, they are not subject to any possible torsion caused by the rotation of the output shaft 3.

[0110] Furthermore, the weight / power ratio offered by the actuator 1 which has just been described is superior to that of the actuators of the prior art.

[0111] This is explained in particular by the fact that the space requirement is reduced thanks to the developed architecture and the position of the different parts.

[0112] For information purposes, the architecture of the actuator according to the invention allows a space saving of around 15% on the diameter, and around 20% on the length, and a weight saving of more than 10%, compared to the actuators of the prior art.

[0113] Tests have also made it possible to demonstrate that, despite smaller dimensions and a lower weight than the actuators of the prior art, the actuator 1 according to the invention has: a continuous torque 50% higher; a maximum torque approximately 13% higher; a maximum rotation speed of the output shaft 265% higher.

Claims

Actuator (1) for robotic arm (110) comprising:a tubular casing (2) extending along a main axis (A);an output shaft (3) extending in the tubular casing (2) along the main axis (A);a reducer (4) coupled to the output shaft (3);a motor (5) mounted in the tubular casing (2) and comprising a stator (501) secured to the tubular casing (2) and a rotor (502) coupled to the reducer (4);an input connection (6) located outside the tubular casing (2), andan output connection (7) located in the tubular casing (2) and connected to the input connection (6) by electrical connection means,characterized in that the connection means comprise a rotating collector (8), and in that the output shaft (3) is hollow to allow the passage of cables (C) joining the connection means to a device external to the actuator (1), and in that it comprises means for guiding the output shaft (3) in rotation,interposed between the output shaft (3) and the tubular casing (2), these guide means comprising a first member (9) and a second member (10), the motor (5) and the reducer (4) being positioned between the first member (9) and the second member (10), the tubular casing (2) having three parts abutted along the main axis (A), including a central part (201), a first lateral part (202) and a second lateral part (303), the central part (201) being received between the first lateral part (202) and the second lateral part (203), each lateral part (202, 203) comprising a shoulder (204) for receiving the guide means, the first lateral part (202) having a conical support (205) extending and tapering in the direction of the main axis (A), the shoulder (204) of the first lateral part (202) being practiced at a distal end of smaller diameter of the conical support (205)., Actuator (1) according to the preceding claim, characterized in that it also comprises a stress sensor (11) configured to know, at any time, the forces applied to the output shaft (3). Actuator according to the preceding claim, characterized in that the stress sensor (11) is mounted integral with the tubular casing (2). Actuator (1) according to any one of the preceding claims, characterized in that at least one of the first member (9) and the second member (10) is a bearing. Actuator (1) according to any one of the preceding claims, characterized in that at least one of the first member (9) and the second member (10) is a plain bearing. Actuator (1) according to any one of the preceding claims, characterized in that the rotating collector (8) includes: a first part (801) carrying at least two metal tracks (802), and a second part (803) carrying at least three brushes (804) each intended to cooperate with one of the metal tracks (802). Robotic arm (110) comprising at least two sections articulated relative to each other by means of an actuator (1) according to any one of the preceding claims.

Images