JP7510836B2 - Power transmission device and robot device - Google Patents

Description

The present invention relates to a power transmission device and a robot device, and is suitable for use in, for example, the joint mechanism of a robot arm.

Conventionally, in humanoid robots, it is common for each joint mechanism of a multi-joint robot arm to be equipped with a single actuator for each rotation axis.

In such robot arms, cables are arranged for power supply and signal transmission to drive and control the end effector at the tip of the arm. These cables are housed inside the robot and connect to each part via inside the robot in order to save space and prevent contact or interference with the arm or peripheral devices.

This cable is a flexible member, and when it is installed inside the robot arm, there is a risk that it may be damaged due to friction with the casing or twisting at the points where it rotates around the joints.

For this reason, in the past, in robots equipped with articulated arms, a cable has been arranged to pass through the hollow part of the robot arm, and a folded part of the cable has been provided around the outer periphery of the motor at the joint, to prevent the cable from twisting or breaking (see Patent Document 1).

In addition, in a robot equipped with an articulated arm, a guide part has been provided on the periphery of the receiving part of the arm, and a flexible cable is guided from one side of the arm to the other side via the guide part, thereby preventing the cable from twisting locally (see Patent Document 2).

JP 2017-131969 A JP 2018-15872 A

However, in robots equipped with articulated arms such as those in Patent Documents 1 and 2, all they do is reduce the flexibility of the cable by preventing excessive load from being applied to the joints when they rotate. This means that there is a limit to the durability of the cable, and there is a problem that it cannot be said to be sufficient for practical use.

The present invention was made in consideration of the above points, and aims to propose a power transmission device and robot device that can reduce the space of the entire device and improve the durability of the cables.

In order to solve the above problem, the present invention provides a pair of actuators each having an output shaft with a drive gear of the same structure engaged thereto, a support frame for fixedly supporting the pair of actuators in a state in which the corresponding drive gears are disposed so as to face each other coaxially and inwardly, a driven rotor having a differential gear engaged with each drive gear of the pair of actuators in a contacting or non-contacting manner and rotating integrally with the differential gear , with a notch formed in the support frame as a movable area , and a cylindrical output shaft engaged with the support frame such that the axial direction is perpendicular to the output shaft of each actuator, and a pair of actuators are moved in response to the rotation of the cylindrical output shaft. The system includes an additional actuator that rotates the support frame together with the actuator, and a power supply control cable that is arranged to pass through a gap formed between a pair of opposing drive gears in the support frame and a hollow portion formed in the driven rotor and the differential gear along the rotation center of the differential gear, via a through hole of a predetermined diameter formed along the axial center of the cylindrical output shaft of the additional actuator and a frame through hole of the same diameter formed in the support frame and communicating with the through hole of the cylindrical output shaft, and a power supply control cable that is arranged to pass through the gap formed between a pair of opposing drive gears in the support frame and a hollow portion formed in the driven rotor and the differential gear along the rotation center of the differential gear, and power is supplied to the pair of actuators and the additional actuator via the power supply control cable.

As a result, in the power transmission device, when the support frame is rotated relative to the additional actuator, the power control cable is not at all affected by the rotational movement and direction of the cylindrical output shaft of the additional actuator, and when the driven rotor is rotated relative to the support frame, the power control cable is not at all affected by the rotational movement and direction of the driven rotor. Therefore, in the power transmission device, the power control cable can be arranged in a movable part having a rotation mechanism without applying any load such as twisting or breaking.

In addition, the present invention includes a control unit that drives and controls each of the pair of actuators and the additional actuator , and the control unit rotates both actuators simultaneously in the same direction to rotate the differential gear and the driven rotor, which are fixed in a non-rotating state, around the output shafts of the pair of actuators as the center of rotation relative to the support frame, while simultaneously rotating both actuators in opposite directions to rotate the differential gear and the driven rotor relative to the support frame.

As a result, in the power transmission device, the control unit can rotate the driven rotor relative to the support frame while simultaneously driving and rotating the pair of actuators to apply double the torque. At this time, the control unit can change the rotation direction of the driven rotor relative to the support frame by switching between driving and rotating the pair of actuators in the same or opposite directions.

Furthermore, in the present invention, instead of simultaneously driving and rotating both actuators in opposite directions, the control unit drives and rotates only one of the actuators in a desired direction to rotate the differential gear and the driven rotor relative to the support frame .

As a result, in the power transmission device, when the driven rotor is rotated integrally in response to the rotation of the differential gear, only one of the pair of actuators is rotationally driven and the other is torque-free, so that the rotational torque of the differential gear can be applied only from one of the actuators.

Furthermore, in the present invention, a robot device equipped with the above-mentioned power transmission device includes first and second arms connected to be rotatable in a specific direction based on a joint portion, the first arm has a support frame , and the second arm has a driven rotor, the joint portion is composed of a pair of actuators, a pair of drive gears, an additional actuator and a differential gear, and a power supply control cable is arranged inside the first arm and the second arm via the joint portion.

As a result, in the robot device, the second arm can be rotated relative to the first arm in a specific direction corresponding to the joint, while the second arm can be rotated relative to the first arm in a twisting direction about a rotation center that is a direction perpendicular to the specific direction. In addition, in the robot device, by applying additional actuators to base joints of the limbs of a humanoid robot, such as shoulder joints and hip joints, it becomes possible to make the entire mechanism of the base joints compact.

The present invention makes it possible to realize a power transmission device and a robot device that can reduce the space required for the entire device and improve the durability of the cables.

1 is a conceptual diagram showing an external configuration of a power transmission device according to a first embodiment. 2 is a cross-sectional view of the power transmission device shown in FIG. 1 from two directions. 2A and 2B are a cross-sectional view and an exploded view showing a configuration of an actuator in the power transmission device. FIG. 2 is a conceptual diagram showing a configuration of a robot arm in the first embodiment. 5A to 5C are cross-sectional views of the robot arm shown in FIG. 4 from two directions. FIG. 11 is a conceptual diagram showing a configuration of a power transmission device according to a second embodiment. FIG. 7 is a conceptual diagram of the robot leg shown in FIG. FIG. 13 is a conceptual diagram of a power transmission device according to another embodiment. FIG. 9 is a cross-sectional view of the power transmission device shown in FIG. 8 . FIG. 13 is a conceptual diagram showing a configuration of a robot device to which a power transmission device according to another embodiment is applied.

One embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of a power transmission device according to a first embodiment Fig. 1 shows a power transmission device 1 according to a first embodiment. Fig. 2(A) and (B) are cross-sectional views of the power transmission device in Fig. 1 taken along arrows A-A' and B-B'. Arrows A-A' and B-B' are perpendicular to each other.

In FIG. 1, the power transmission device 1 has a housing portion 3 on which a pair of actuators 2 are mounted, and a driven rotor 4 that is rotatably engaged with the housing portion 3 in two different rotational directions. In FIG. 1, the housing ends of the housing portion 3 and the driven rotor 4 are omitted.

As shown in Figures 2(A) and (B), the housing section 3 has a pair of actuators 2, each of which has an identical bevel gear 6 engaged at the tip of the output shaft 5, and the actuators 2, each of which has the same structure, are fixed and held in place with the corresponding bevel gears 6 positioned coaxially and facing inward.

The driven rotor 4 has a differential gear 15 that meshes with each bevel gear 6 of the pair of actuators 2, and rotates together with the differential gear 15.

A power supply control cable 20 is arranged to pass through the gap G1 formed between a pair of opposing bevel gears 6 in the housing portion 3 and the hollow portion H1 formed along the rotation center of the differential gear 15 in the driven rotor 4 and the differential gear 15. The pair of actuators 2 in the housing portion 3 are each supplied with power and receive control signals, etc., via the power supply control cable 20.

In this way, in the power transmission device 1, the power supply control cable 20 is arranged to pass through the gap G1 in the housing portion 3 and the hollow portion H1 in the driven rotor 4 including the differential gear 15, so that when the driven rotor 4 is rotated relative to the housing portion 3, the power supply control cable 20 is not affected at all by the rotational motion and direction of the driven rotor 4.

Therefore, in the power transmission device 1, it is possible to arrange the power supply control cable 20 in the movable part having the rotation mechanism without applying any load such as twisting or breaking.

As shown in Figures 3(A) and (B), the actuator 2 is, for example, a flat brushless DC motor, and includes a stator 30 having an armature winding, and a rotor 40 including a group of permanent magnets rotatably supported relative to the stator.

The rotor 40 of this actuator 2 is composed of a Halbach array of permanent magnets (a circular array of individual magnets) 41 and an annular band 42 made of a high magnetic susceptibility material that surrounds the outer periphery of the permanent magnets 41.

Here, the Halbach array permanent magnet group 41 is a combination of a main magnetic pole magnet in which north and south poles are alternately arranged in the radial direction of the rotor 40, and auxiliary magnets magnetized in a direction other than the radial direction (circumferential direction) on both circumferential sides of the main magnetic pole magnet, and by optimizing the direction of the magnetic poles, it is possible to strengthen the magnetic field strength in a specific direction.

Each individual magnet in the permanent magnet group 41 is arranged such that the magnetic field of adjacent magnets in an array segment (e.g., a unit of 8 magnets) is tilted at 45 degrees from each other, so that the composite magnetic field is generated perpendicular to the array direction (towards the inner center) and the magnetic field shape approximates a sine wave.

The annular band 42 is designed to have a predetermined thickness around its outer periphery so as to confine the magnetic field lines emanating from the permanent magnet group 41 and increase the internal magnetic field.

The stator 30 of the actuator 2 has a ring-shaped fixed pole 31 consisting of an armature winding wound around each iron core, and a reducer 32 that converts the rotational speed of the rotor 40 of the actuator 2 to a predetermined reduction ratio and outputs it. The ring-shaped fixed pole 31 is designed to ensure the maximum magnetic field in relation to the rotor by the dimensions, volume, and outer diameter of the core and the number of cores arranged (number of teeth). The ring-shaped fixed pole 31 also has a ring member that supports each core in an annular shape and has a thickness designed to confine the generated magnetic field and prevent magnetic flux leakage in the direction of the center of rotation.

In addition, in the actuator 2, the number of individual magnets in the permanent magnet group 41 of the rotor 40 and the number of cores (number of poles) of the ring-shaped fixed pole 31 of the stator 30 are set to have optimal magnetic pole pairs so that the driving torque can be maximized.

The motion transmission device 1 has a built-in actuator control unit (not shown) consisting of an MCM (Multi-Chip Module) equipped with a CPU (Central Processing Unit), memory, etc., and is configured to drive and control the pair of actuators 2.

The actuator control unit controls the actuators 2 to rotate simultaneously in the same direction, rotating the differential gears 15 and driven rotors 4, which are fixed in a non-rotating state, around the output shafts 5 of the pair of actuators 2 as the center of rotation relative to the housing unit 3, while simultaneously rotating the actuators 2 in the opposite direction, rotating the differential gears 15 and driven rotors 4 relative to the housing unit 3.

As a result, in the power transmission device 1, the actuator control unit can rotate the driven rotor 4 relative to the housing part 3 while simultaneously driving and rotating the pair of actuators 2 to apply double the torque. In this case, the actuator control unit can change the rotation direction of the driven rotor 4 relative to the housing part 3 by switching between driving and rotating the pair of actuators 2 in the same or opposite directions.

(2) Configuration of Robot Arm in First Embodiment A case where the power transmission device 1 shown in Fig. 1 is applied to a robot arm 60 will be described with reference to Fig. 4 and Figs. 5(A) and (B). Figs. 5(A) and (B) are cross-sectional views of the robot arm 60 in Fig. 4 taken along the lines of arrows A-A' and B-B'.

In the robot arm 60, the power transmission device 1 is applied to the shoulder joint and elbow joint, and the power control cable 20 drawn from the robot device body is arranged on the hand side through both the shoulder joint and elbow joint.

That is, as shown in FIG. 4, the robot arm 60 includes a shoulder body frame 61 and an upper arm arm 62 connected to be rotatable in a specific direction with the power transmission device 1 serving as the shoulder joint, and an upper arm arm 62 and a forearm arm 63 connected to be rotatable in a specific direction with the power transmission device 1 serving as the elbow joint.

As shown in Figures 5(A) and (B), in the power transmission device 1 that serves as the shoulder joint, the housing 3 constitutes a part of the shoulder body frame 61, the driven rotor 4 constitutes a part of the upper arm arm 62, and the shoulder joint is composed of a pair of bevel gears 6 and a differential gear 15. The power supply control cable 20 is arranged inside the shoulder body frame 61 and the upper arm arm 62 via the shoulder joint.

In this way, in the robot arm 60, the power transmission device 1 can rotate the upper arm arm 62 relative to the shoulder body frame 61 in a specific direction corresponding to the shoulder joint, while also rotating the upper arm arm 62 relative to the shoulder body frame 61 in a twisting direction with the perpendicular direction to the specific direction as the center of rotation.

In the power transmission device 1, which is the elbow joint, the housing 3 constitutes a part of the upper arm arm 62, and the driven rotor 4 constitutes a part of the forearm arm 63, and the elbow joint is composed of a pair of bevel gears 6 and a differential gear 15. The power supply control cable 20 drawn out through the shoulder joint is arranged inside the upper arm arm 62 and the forearm arm 63 via the joint.

In this way, in the robot arm 60, the power transmission device 1 can rotate the forearm arm 63 relative to the upper arm arm 62 in a specific direction corresponding to the elbow joint, while rotating the forearm arm 63 relative to the upper arm arm 62 in a twisting direction with the perpendicular direction to the specific direction as the center of rotation.

(3) Configuration of the power transmission device in the second embodiment Figures 6(A) and (B) show a power transmission device 70 in the second embodiment. In the power transmission device 70 shown in Figures 6(A) and (B), a housing portion 71 on which a pair of actuators 2 are mounted has a driving pulley 72 engaged with the output shaft 5 of the actuator 2, and a pair of bevel gears (driven pulleys) 74 of the same structure that are engaged with the driving pulleys 72 via wires 73, and that face each other coaxially and inwardly.

In this housing part 71, a differential gear 75 is meshed with each bevel gear 74, and a driven rotor 76 rotates integrally with the differential gear 75. In Figures 6 (A) and (B), the housing end of the driven rotor 76 is omitted.

A power supply control cable 20 is arranged to pass through the gap formed between a pair of opposing bevel gears 74 in the housing part 71 and through a hollow portion formed along the rotation center of the differential gear 75 in the driven rotor 76 and the differential gear 75. The pair of actuators 2 in the housing part 71 are each supplied with power via the power supply control cable 20.

In this way, in the power transmission device 70, the power supply control cable 20 is arranged to pass through the gap in the housing portion 71 and the hollow portion in the driven rotor 76 including the differential gear 75, so that when the driven rotor 76 is rotated relative to the housing portion 71, the power supply control cable 20 is not affected at all by the rotational motion and direction of the driven rotor 76.

Therefore, in the power transmission device 70, it is possible to arrange the power supply control cable 20 in a movable part having a rotation mechanism without applying any load such as twisting or breaking.

The actuator 2 and the structure of the actuator 2 are the same as those shown in Figs. 3(A) and (B) above. The actuator control unit in the power transmission device 70 controls the actuators 2 to rotate simultaneously in the same direction, rotating the differential gears 75 and driven rotors 76, which are fixed in a non-rotating state, around the output shafts 5 of the pair of actuators 2 as the center of rotation relative to the housing unit 71, while simultaneously rotating both actuators 2 in the opposite direction, rotating the differential gears 75 and driven rotors 76 relative to the housing unit 71.

As a result, in the power transmission device 70, the actuator control unit can rotate the driven rotor 76 relative to the housing part 71 while simultaneously driving and rotating the pair of actuators 2 to apply double the torque. In this case, the actuator control unit can change the rotation direction of the driven rotor 76 relative to the housing part 71 by switching between driving and rotating the pair of actuators 2 in the same or opposite directions.

(4) Configuration of Robot Leg in Second Embodiment A case where the power transmission device 70 shown in Figures 6(A) and (B) described above is applied to a robot leg 80 will be described with reference to Figures 7(A) and (B). In the robot leg 80, the power transmission device 70 is applied to the knee joint and the ankle joint, respectively, and the power supply control cable 20 drawn out from the robot device main body is arranged to pass through both the knee joint and the ankle joint and to be routed to the hand side.

In addition, in this robot leg 80, the power transmission device 1 according to the first embodiment described above is applied to the hip joint, and the driven rotor 4 of the power transmission device 1 is fixed integrally to the hip joint side of the thigh frame 81 serving as a housing part.

The robot leg 80 comprises a thigh frame 81 and a shin frame 82 connected to the power transmission device 70, which serves as the knee joint, so as to be rotatable in a specific direction, and a shin frame 82 and an instep frame 83 connected to the power transmission device 70, which serves as the ankle joint, so as to be rotatable in a specific direction.

In the power transmission device 70, which is the knee joint part, the housing part 71 constitutes a part of the thigh frame 81, and the driven rotor 76 constitutes a part of the shin frame 82, and the knee joint part is composed of a pair of bevel gears 74 and a differential gear 75. The power supply control cable 20, which is pulled out through the hip joint part, is arranged inside the thigh frame 81 and the shin frame 82 via the shin joint part.

In this way, in the robot leg 80, the power transmission device 70 can rotate the shin frame 82 relative to the thigh frame 81 in a specific direction corresponding to the knee joint, while also rotating the shin frame 82 relative to the thigh frame 81 in a twisting direction with the perpendicular direction to the specific direction as the center of rotation.

In the power transmission device 70, which serves as the ankle joint, the housing 71 constitutes part of the shin frame 82, and the driven rotor 76 constitutes part of the instep frame 83, with the ankle joint being made up of a pair of bevel gears 74 and a differential gear 75. The power supply control cable 20 is pulled out via the knee joint and is arranged inside the shin frame 82 and instep frame 83 via the joint.

In this way, in the robot leg 80, the power transmission device 70 can rotate the instep frame 83 relative to the shin frame 82 in a specific direction corresponding to the elbow joint, while also rotating the instep frame 83 relative to the shin frame 82 in a twisting direction with the perpendicular direction to the specific direction as the center of rotation.

(5) Other Embodiments In the above-mentioned first and second embodiments, the two types of power transmission devices 1, 70 are applied to the robot arm 60 and the robot leg 80. However, the present invention is not limited to this, and may be widely applied to robot devices having various joints, such as human-type or animal-type robot devices.

For example, in a humanoid robot device (not shown), it can be applied not only to the shoulder joints and elbow joints, but also to the waist joints and the connection parts with the drive wheels.

In the above-mentioned first embodiment, the housing portion 3 that holds the pair of actuators 2 in the power transmission device 1 is fixed, but the present invention is not limited to this. The power transmission device may be directly rotated integrally with the entire housing portion.

That is, for example, the power transmission device 100 shown in Figures 8 and 9 has a support frame 102 that supports a pair of actuators 2 inside a housing part 101 that has a generally spherical shell structure as a whole. This support frame 102 has a notch 102A formed at one end that corresponds to the movable range of the driven rotor 4, and has a structure in which the output shaft 104 of an additional actuator 103 is engaged at the other end.

The driven rotor is omitted from FIG. 8. The pair of actuators 2 and the corresponding bevel gears 6 may have the same configuration as the power transmission device 1 in the first embodiment. Although not shown, the driven rotor 4 and differential gear 15 may also have the same configuration as the motion transmission device 1 in the first embodiment.

This additional actuator 103 has a through hole 104A of a predetermined diameter formed along the axial center of the output shaft 104. The support frame 102 also has a through hole 102B of the same diameter that communicates with the through hole 104A of the output shaft 104. This allows the power supply control cable 20 to be inserted through the through hole 104A of the output shaft 104 of the additional actuator 103 and the through hole 102B of the support frame 102.

As a result, the power transmission device 100 can be arranged so that the power supply control cable 20 drawn from the outside is inserted through the through hole 104A of the output shaft 104 of the additional actuator 103, through the gap G1 formed between a pair of opposing bevel gears 6 in the housing portion 101, and through the hollow portion H1 formed along the rotation center of the driven rotor 4 and the differential gear 15 in the differential gear 15.

Therefore, in the power transmission device 100, when the housing part 101 is rotated relative to the additional actuator 103, the power control cable 20 is not affected at all by the rotational movement and direction of the output shaft 104 of the additional actuator 103, and when the driven rotor 4 is rotated relative to the housing part 101, the power control cable 20 is not affected at all by the rotational movement and direction of the driven rotor 4. Therefore, in the power transmission device 100, it is possible to arrange the power control cable 20 in a movable part having a rotation mechanism without applying any load such as twisting or breaking.

The power transmission device 100 including such an additional actuator 103 can be applied to the base joint of a limb of a humanoid robot, such as the shoulder joint or hip joint, as a robot device 110 as shown in FIG. 10, making it possible to make the entire mechanism of the base joint compact.

Furthermore, in the power transmission devices 1, 70 of the first and second embodiments described above, instead of simultaneously driving and rotating both actuators 2 in opposite directions, the actuator control unit may drive and rotate only one of the actuators 2 in a desired direction to rotate the differential gears 15, 75 and the driven rotors 4, 76 relative to the housing parts 3, 71.

As a result, in the power transmission device 1, 70, when the driven rotors 4, 76 are rotated integrally in response to the rotation of the differential gears 15, 75, only one of the pair of actuators 2 is rotationally driven and the other is torque-free, so that the rotational torque of the differential gears 15, 75 can be applied only from one of the actuators 2.

In the above-mentioned first and second embodiments, the actuator control unit is built into the power transmission device 1, 70. However, the present invention is not limited to this. An actuator control unit may be applied to control the power transmission device 1, 70, 100 and a robot device (including a robot arm and a robot leg) including the power transmission device 1, 70, 100 in whole or in part. In this case, the control signal from the actuator control unit may be transmitted to each actuator 2 via a signal line included in the power supply control cable 20.

In addition, in the power transmission devices 1, 70, 100 in the first and second embodiments described above, the drive gears engaged with the pair of actuators 2 are configured from bevel gears 6, 74, and the differential gears rotating integrally with the driven rotors 4, 76 are configured from differential gears 15, 75. However, the present invention is not limited to this, and the drive gear may be a non-contact coaxial center transmission gear such as a magnet gear or a contact coaxial center transmission gear such as a friction roller, in addition to the bevel gear, and the differential gears engaged in contact or non-contact with the drive gear may have a differential transmission mechanism according to the drive gear.

Furthermore, in the power transmission device 70 according to the second embodiment, the housing portion 71 on which the pair of actuators 2 are mounted is described as having a drive pulley 72 engaged with the output shaft 5 of each of the actuators 2, and each of the drive pulleys 72 and the drive gear (driven pulley) 74 engaged via a wire 73, but the present invention is not limited to this, and in addition to the drive pulleys and wires, various configurations of drive ropes and rope-like bodies (belts, ropes, etc.) may be used as the transmission mechanism.

1, 70, 100...Power transmission device, 2...Actuator, 3, 71, 101...Housing section, 4, 76...Driven rotor, 5, 104...Output shaft, 6, 74...Bevel gear, 15, 75...Differential gear, 20...Power supply control cable, 30...Stator, 31...Ring-shaped fixed pole, 32...Reduction gear, 40...Rotor, 41...Permanent magnet group, 42...Annular band, 60...Robot arm, 61...Shoulder body frame, 62...Upper arm arm, 63...Forearm arm, 72...Driving pulley, 73...Wire, 80...Robot leg, 81...Thigh frame, 82...Shin frame, 83...Instep frame, 110...Robot device, 102...Support frame, 103...Additional actuator.

Claims (4)

A pair of actuators, each having an output shaft connected to a drive gear of the same structure,
a support frame that fixes and supports the pair of actuators in a state in which the corresponding drive gears are disposed coaxially and inwardly facing each other;
a driven rotor having a differential gear that is engaged with the drive gears of the pair of actuators in a contact or non-contact manner, and that rotates integrally with the differential gear and has a notch formed in the support frame as a movable region ;
an additional actuator having a cylindrical output shaft engaged with the support frame such that an axial direction of the additional actuator is perpendicular to the output shafts of the actuators, and rotating the support frame together with the pair of actuators in response to rotation of the cylindrical output shaft;
a power supply control cable arranged to pass through a gap formed between a pair of opposing drive gears in the support frame and a hollow portion formed in the driven rotor and the differential gear along the rotation center of the differential gear, via a through hole of a predetermined diameter formed along the axial center of the cylindrical output shaft of the additional actuator and a frame through hole of the same diameter formed in the support frame and communicating with the through hole of the cylindrical output shaft, wherein power is supplied to the pair of actuators and the additional actuator via the power supply control cable. a control unit that drives and controls the pair of actuators and the additional actuator ,
2. The power transmission device according to claim 1, wherein the control unit simultaneously drives and rotates both of the actuators in the same direction to rotate the differential gear and the driven rotor, which are fixed in a non-rotating state, relative to the support frame about the output shafts of the pair of actuators as centers of rotation, while simultaneously drives and rotates both of the actuators in opposite directions to rotate the differential gear and the driven rotor relative to the support frame . 3. The power transmission device according to claim 2, wherein the control unit rotates only one of the actuators in a desired direction to rotate the differential gear and the driven rotor relative to the support frame , instead of simultaneously driving and rotating both of the actuators in opposite directions. A robot device comprising the power transmission device according to any one of claims 1 to 3,
The robot has a first and a second arm connected to each other so as to be rotatable in a specific direction with respect to a joint portion as a reference,
the first arm has the support frame and the second arm has the driven rotor;
the joint portion is composed of a pair of the actuators, a pair of the drive gears , the additional actuator, and the differential gear;
the power supply control cable is arranged inside the first arm and the second arm via the joint portion.

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