JP4273335B2 - Robot arm - Google Patents

Description

  The present invention relates to a robot arm having a plurality of joints, a rotary joint device, and a wrist device for performing various operations in a non-manufacturing industry field including a daily life field in contact with a person.

  Industrial robots use many electric wires for actuators, sensors, and the like, but these wires are bent and twisted by the movement of joints. In order to reduce bending and twisting, a contrivance has been made such as making the joint shaft into a hollow structure and passing an electric wire therethrough (for example, Patent Document 3). However, there is a limit to the amount of rotation of the joint because bending and twisting are not completely eliminated.

  On the other hand, as a method for eliminating electric wire twist due to rotation and maintaining electrical connection, a so-called slip ring mechanism using a sliding contact of a conductive member that slides with rotation is generally used. Is used for transmitting sensor information and supplying current to a hand tool (for example, Patent Documents 4 and 5). However, if it is attempted to maintain the electrical connection of sensors and the like arranged at each joint from the base of the arm, the joint on the base side requires a larger number of poles of the slip ring, and there is a limit to miniaturization and cost reduction. Arise.

  On the other hand, by placing a local controller near the actuator of each joint so that sensor information acquisition and actuator commands can be processed locally, by connecting each controller using ARCNET, CAN bus, etc. Wiring to the joint can be reduced to only the power line and the communication line (for example, Non-Patent Document 2). However, although wiring is necessary, since the wiring is necessary, the operation of the joint is limited, and an arbitrary continuous operation cannot be performed.

  In addition, as an example of controlling the robot arm, not a simple teaching playback but an operation control adapted to the external force, there is a method using a 6-axis force sensor attached to the wrist of the robot arm. The control of the corresponding object shape is performed. However, only the detection of the force acting on the tool can control the operation characteristics of the tool, but it cannot detect the force acting on the link in the middle of the robot arm, so this method adapts to people and the environment for the purpose of ensuring safety. I can't let you. On the other hand, as a method of softly controlling the joint according to the external force applied to each joint itself for the purpose of interpersonal safety or the like, a method using a torque sensor (such as Patent Document 2) installed in the joint itself (Non-Patent Document 4, 5) and a mechanical variable rigidity mechanism (Non-patent Document 1). However, since the adaptation operation cannot be performed at the rotation limit of the joint, there is a problem that safety cannot be ensured sufficiently.

  Among the robot arms, there is a so-called redundant degree of freedom arm having a degree of freedom capable of deforming the shape of the arm itself, that is, the self shape, in addition to the 6 degrees of freedom of the position and orientation of the hand (for example, Patent Document 1, Non-Patent Document 1). Patent Documents 1, 3, 4, 5). For example, an arm configured with 7 degrees of freedom similar to a human arm can change the position of the elbow joint to some extent on a circular trajectory around the axis connecting the wrist joint and shoulder joint even if the position and orientation of the hand are fixed. (Patent Document 1). Conversely, even if the position of the hand is determined and the elbow position is fixed, the three degrees of freedom of the hand posture can be changed to some extent. If the advantage of such redundancy is used, the elbow position can be moved to some extent in a state where there is no interference in the work, so that the workability is higher than that of a normal 6-DOF arm. In addition, by changing the self-shape while adapting to the external force while maintaining the hand work, the collision force with the person and the environment can be softened and the safety can be improved. However, if there is a joint rotation limit, the state where you can enjoy the advantage of this redundancy is limited to the state where all joints are sufficiently away from the rotation limit. It is not possible to take advantage of the features of.

U.S. Pat.No. 4,999,553 JP 09-184777 A JP 2002-79487 A Japanese Patent Laid-Open No. 2003-117877 JP 2003-285167 A Morita, Iwata, Ueda, Hadano, “Development of 7-DOF MIA Arm”, Proc. Of the 1st Robotics Symposia, pp.179-184, 1996. C.J.J.Paredis, H.B.Brown, P.K.Khosla, “A rapidly deployable manipulator system”, Robotics and Autonomous Systems, vol.21, pp.289-304, 1997. W.T.Townsend and J.A.Guertin, “Teleoperator slave-WAM design methodology”, Industrial Robot, vol.26, no.3, pp.167-177, 1999. Hattori, Hashimoto, Kamada, "Development of a humanoid manipulator with a joint torque sensor", Proceedings of SICE System Integration Division Annual Conference, pp.29-30, 2001. M. Hashimoto, T. Hattori, M. Horiuchi, T. Kamata, “Development of a Torque Sensing Robot Arm for Interactive Communication”, Proc. 2002 IEEE Int. Workshop on Robot and HumanInteractive Communication, 2002.

  Since the conventional robot arm is intended for use in industrial applications, it is difficult to use it as it is for work expected in non-manufacturing industries other than factories such as human life support fields. The reason is

  (1) Teaching playback work is mainly performed in the factory, but in many non-manufacturing industries, the work conditions are often not constant, and various operations according to the situation at the site are required. I cannot make an action plan. For example, if the user tries to continuously operate the position and orientation of an object gripped by the robot end effector while keeping the grip, the target hand position and orientation are within the movable range in the Cartesian coordinate system. Even in such a case, there is a great restriction on an arbitrary operation such that the joint reaches the limit of movement depending on the operation history, or the link in the middle of the arm interferes with the environment and the work cannot be continued.

(2) In the manufacturing industry, priority is given to work speed and high accuracy, so the robot arm is designed to increase the overall rigidity. This is good if it is based on the premise that people do not enter the movable range, but in non-manufacturing industries, it is assumed that the robot is often in contact with people and the environment, so it worked in the middle of the arm. It is dangerous for conventional industrial robots that do not have a structure that can adapt to force.
The point is mentioned.

  In particular, regarding (1), the movable limit of the joint itself is caused by interference between adjacent links and twisting of the electric wire inside the arm. That is, if you try to bend the links in the same plane by rotating joints, the links will always interfere with each other. The joints cannot be rotated indefinitely due to the twisting of the wires. On the other hand, the problem of interference between the arm and the environment becomes more prominent in a normal 6-DOF arm. Particularly in the vicinity of the singular point, even if the hand posture is slightly changed, the entire arm is greatly shaken. Therefore, it is necessary to secure a wide free space in advance for an arbitrary operation in which the singular point cannot be predicted.

  The present invention solves such a problem, and (i) to improve workability for a robot arm for a non-manufacturing industry field including a life support field, and to realize an arbitrary work according to the situation on the spot (1) Make the structure that can adapt to external force in order to improve the safety against people and the environment, and make the structure that can limit the joint movement as much as possible and avoid the interference between the arm and the environment. It is an object.

  The rotary joint device for a robot arm according to the present invention has an angle detector, a torque detector, an actuator, and a local controller to drive two links that are rotatably connected, and links while sliding with the rotation of the joint. A slip ring mechanism for maintaining an electrical connection therebetween. Based on the angle and torque values obtained from the angle detector and torque detector, control commands for the actuator are simultaneously issued to realize control related to the position, torque, stiffness, and viscosity characteristics specified by the master controller. It is characterized by being able to rotate indefinitely while calculating on the local controller and maintaining the electrical connection between the links.

A robot arm according to the present invention is characterized by having one or more of the above-described rotary joint devices to enable a continuous turning motion adapted to an external force.
The wrist device for a robot arm according to the present invention includes the three rotary joint devices in a plane in which the rotation axes of the adjacent joint devices are orthogonal to each other and the rotation axes of the joint devices at both ends are separated from each other. Power is supplied to the local controllers of the three joint devices by connecting the three joint devices in order to rotate with respect to the rotation shaft of the intermediate joint device. In addition, data communication between the local controller and the host controller is performed, and it is possible to arbitrarily change the hand posture while adapting to external force while providing electrical connection to various expansion devices. Features.

  In general, a robot arm has a plurality of links connected by a plurality of joint devices, and the position and posture of the hand in the orthogonal coordinate system are determined by the operation of each joint device. Normally, a specific operation for manipulating an object or environment is executed by changing the position and posture of the hand, but the target state is in the hand position and posture space that the robot arm can take in the Cartesian coordinate system. Even if there is, since the movement limit is reached depending on the motion history of each joint device in the motion space on the joint coordinate system, only the hand position / posture is concerned even if the work interest is only the hand position / posture. It is not possible to perform arbitrary operations in consideration of the above.

  In addition, in a redundant degree-of-freedom robot arm having more than six degrees of freedom, which is necessary to arbitrarily determine the position and orientation of the hand, the position and orientation of the hand are kept constant by using redundancy. The self-shape of the robot arm can be changed, or the hand posture can be changed while keeping the self-shape of the arm substantially constant. Due to such characteristics, it is possible to avoid interference with the environment while keeping the hand work, or to perform the hand work by inserting an arm in a limited space. Also, by controlling while detecting the external force acting in the middle of the arm, it is possible to adapt to the external force by the deformability of self shape while maintaining the hand work when the arm contacts the person or the environment, Environmental safety can be improved. However, even here, since the joint has a movable limit, the self-shape can be changed only within the movable range of each joint. This is not a problem in the case of specific work in a factory where appropriate operations can be planned in advance, but in non-manufacturing sectors such as daily life support, in many cases Since it is required to continuously perform various actions according to the situation, the conventional redundant degree-of-freedom arm reaches the self-shape deformation limit during operation, and self-shape operation taking advantage of the redundancy degree of freedom. It becomes impossible to adapt to external force.

  According to the present invention, since the rotary joint device includes the angle detector, the torque detector, the actuator, and the local controller, the local controller can directly acquire the joint angle and the torque value. By executing the control algorithm above, the control related to the position, torque, stiffness, and viscosity characteristics specified by the master controller can be executed in a closed form in the joint device. A rotary joint device capable of adapting to an external force while performing stably can be provided. In addition, since it has a slip ring mechanism that maintains the electrical connection between the links while sliding along with the rotation of the joint, the electrical connection can be maintained regardless of the rotation angle of the joint. It is possible to rotate the joint indefinitely while maintaining power supply and communication connection to the device.

  In addition, according to the present invention, an electric motor and a harmonic drive speed reducer are used as an actuator, and a strain sensor pasted on the flexspline of the harmonic drive speed reducer is used as a torque detector, thereby adapting to an external force and infinite rotation. Possible rotary joint devices can be made small and lightweight.

  In addition, according to the present invention, the robot arm has one or more rotary joint devices that can adapt to an external force and can rotate infinitely, thereby enabling a continuous turning operation that adapts to the external force. The workability and safety of the robot arm can be improved.

  Further, according to the present invention, three rotary joint devices that adapt to an external force and can rotate infinitely are arranged in a plane in which the rotation axes of adjacent joint devices are orthogonal to each other and the rotation axes of joint devices at both ends are separated from each other. The joint device is coupled so as to rotate with respect to the rotation shaft of the intermediate joint device, and is electrically connected, so that any joint device can be continuously rotated without any collision between the joint devices. A wrist device is obtained. In the prior art, there are restrictions on the hand postures and posture changes that can be realized due to the limitations of individual joint angles, but this configuration eliminates restrictions on the hand postures that can be taken, and arbitrary continuous posture changes Will be able to give. Furthermore, since rigidity and viscosity can be set for each joint device, it is possible to perform an adaptation operation to an external force. Furthermore, since the joint device at the final stage can provide electrical connection to various expansion devices, a 6-axis force sensor, an end effector, or the like can be attached to the tip of the wrist device. Even if it is attached, the wiring for that purpose does not affect the movement of the wrist device or the entire robot arm.

  In addition, according to the present invention, a redundant degree of freedom configuration including a wrist device and having a rotary joint that can adapt to an external force of four or more axes in addition to the wrist device results in a rotation limit of the rotary joint of the wrist device. It is possible to increase the range in which the self-shape can be changed while adapting to external force by eliminating the robot arm motion restrictions. In addition, when teaching the robot arm's repeated motions with redundant degrees of freedom, it is necessary to teach not only the position and orientation of the hand, but also the robot's self-shape. Therefore, even without using a teaching pendant, it is possible for a person to directly grasp the robot arm link by hand and apply force to directly change the robot arm's hand position / posture and teach it. It becomes.

  Further, according to the present invention, a redundant robot arm having 7 degrees of freedom is composed of a shoulder device including three rotary joints, an elbow device including one rotary joint, and a wrist device. The rotary shafts are connected so as to be orthogonal to the rotary shafts of the adjacent rotary joints, and at least the rotary joints at both ends of the shoulder device can adapt to the external force and can rotate infinitely other than the three rotary joints of the wrist device. The result is that any continuous change can be made to the proximal position of the wrist device by using the rotary joint device, and any continuous change can be made to the hand posture with the wrist device. As described above, any continuous change can be applied to each of the hand position, hand posture, and self-shape of the robot arm except for the singular state while adapting to the external force.

  A general configuration of a joint device 1 embodying the present invention is shown in FIG. The illustrated joint device 1 includes an actuator, devices such as an angle detector and a torque detector, a local controller 8 that locally controls the operation of the joint device 1, and a slip ring. A power line 9a and a communication line 10a are connected to the local controller 8, and a power line 9b and a communication line 10b are provided to the joint end via a slip ring regardless of the rotation angle of the joint. However, when the communication circuit on the local controller 8 is configured to enable wireless communication, the communication lines 10a and 10b are not necessary.

The joint device 1 shown in FIG. 2 is a more specific example, and includes a DC motor 2 as an actuator and a wave generator 3, a flex spline 4 and a circular spline 5 for decelerating the rotation speed. When using a harmonic drive decelerator, an encoder 6 for detecting the rotation angle of the motor as an angle detector, and a strain gauge 7 installed on the flexspline 4 of a harmonic drive (registered trademark) decelerator as a torque detector Is shown. The DC motor 2, the encoder 6, and the strain gauge 7 are connected to a local controller 8 that locally controls the operation of the joint device 1. The local controller 8 measures a torque from a change in resistance of the strain gauge 7 and a motor amplifier circuit for driving the DC motor 2, a counter circuit for counting pulses from the encoder 6, in addition to an arithmetic device that calculates a control algorithm. And a communication circuit for performing communication with an external controller. In addition, power is supplied by the power line 9a and the communication line 10a connected to the local controller 8, and data can be transmitted to and received from the external controller. Further, the rotation angle of the joint can be adjusted via a slip ring mechanism described later. Regardless, the power line 9b and the communication line 10b are provided at the joint end.

  A mechanism for rotating the joint will be described. First, the front link 11 is fixed integrally with the local controller 8, the case 13, the flex spline 4, the DC motor 2, and the encoder 6. Then, when a voltage is applied to the DC motor 2 by the local controller 8 and the motor shaft 14 rotates, the wave generator 3 fixed to the motor shaft 14 rotates, and a wave is generated due to the deformation of the flex spline 4 and the circular The spline 5 rotates at a speed obtained by multiplying the rotational speed of the motor shaft 14 by a certain reduction ratio. The circular spline 5 and the rear link 12 are fixed integrally. As a result, the front link 11 and the rear link 12 relatively rotate.

  Detection of torque acting on the joint can be performed according to Patent Document 2. That is, the joint torque is detected by detecting the deformation generated in the diaphragm portion of the flexspline 4 with the strain gauge 7.

  The slip ring mechanism will be described. An insulating ring 16 made of an insulating material is fixed on a sleeve 15 that rotates together with the circular spline 5, and a plurality of current collecting rings 17 made of a conductive material are fixed while being insulated by the insulating ring 16. Through a hole drilled through the insulating ring 16 and the sleeve 15, the power line 9 b and the communication line 10 b connected to the inner surface of the current collecting ring 17 are passed through the sleeve 15, and the sleeve 15, the circular spline 5, The power supply line 9b and the communication line 10b are wired to the rear link 12 side through a hole opened through the rear link 12. On the other hand, the brush 18 connected to each of the power supply line 9c and the communication line 10c taken out from the local controller 8 is attached to the case 13 while holding the insulator 19 so as to keep sliding contact with the corresponding current collecting ring 17. And fix. Even if the front link 11 and the rear link 12 rotate with each other by this slip ring mechanism, it is possible to supply power to the device ahead of the joint device 1 and maintain communication without depending on the rotation amount.

  Then, by connecting the joint device 1 of FIG. 1 or 2 mechanically and electrically, a mechanism with multiple degrees of freedom can be realized without increasing the number of wires. The block diagram of FIG. 3 shows wiring during operation of an n-joint robot arm to which an end effector is attached. Data can be sent and received between the master controller and the local controller via serial communication via the communication line. The control mode and parameters of the local controller can be set from the master controller, and the master controller can acquire various state quantities from the local controller. be able to.

  In addition, a 6-axis force sensor is connected to the local controller of the end effector to measure the force and moment acting on the end effector, and a tactile sensor attached to the link surface near the joint is connected to the local controller of each joint. By detecting the contact force on the link and changing the control parameters of each joint while using the information on those forces, moments, and contact forces with the master controller, it is possible to adapt to external forces with high accuracy. It is also possible to extend to various configurations.

  Next, an example of a wrist device is shown in FIG. The wrist device 41 of FIG. 4 uses three joint devices 1 (42, 43, 44) as shown in FIG. 1 or FIG. 2 and the three axes (45, 46, 47) adjacent to each other are orthogonal to each other. In addition, the shafts (45, 47) at both ends are configured to be able to completely pivot with respect to the intermediate shaft 46 in a plane sufficiently separated from each other. According to this configuration, unlike the conventional wrist device, it is not limited by the rotation limit of the joint. Therefore, it is possible to give any hand posture change from any hand posture regardless of the operation history.

  By constructing such a control law, it is possible to set the apparent stiffness and viscosity of the joint, and at the same time, if the target joint torque and the actual joint torque match, F2 will be zero and position control will be performed correctly according to the F1 term When an external force is applied and a new joint torque is generated when the operation is in an equilibrium state, force control is performed so as to reduce the magnitude of the joint torque by the term of F2. As a result, the joint position can be controlled while adapting to the external force. In addition, when such a joint is connected and configured as a robot arm, the force control at each joint can be processed at high speed by the local controller, so that stable control that is not easily affected by communication delay is possible. . On the other hand, if the angle of each joint is acquired by the master controller, the entire arm is subjected to statics or dynamics calculation, and Ft is given so as to compensate for the torque acting on the joint by gravity or inertial force or Coriolis force, The impedance of each joint can be controlled at the same time while accurately controlling the position of the joint.

  In addition, as an example of configuring the robot arm with redundant degrees of freedom, the robot arm 61 in FIG. 6 includes a torque detector in addition to the three axes (66 to 68) of the wrist device having the same configuration as the wrist device 41 in FIG. This shows a case of a seven-degree-of-freedom configuration in which there are four rotational joints (62 to 65) and the rotational axes of all adjacent rotational joints are orthogonal to each other. In such a configuration, there is a degree of freedom that the self-shape can be changed even if the six degrees of freedom of the position and orientation of the hand are fixed, and a technique such as the impedance control described above is applied to all joints by a torque detector. Therefore, even if the position and orientation of the hand is fixed, it is possible to allow the robot arm to adapt to the collision force with the environment due to the self-deformability of the robot arm. Therefore, the operation of the wrist device is not restricted, and an adaptation operation that effectively uses the movable range of joints other than the wrist device is possible.

  Also, in general, if you want to teach repetitive motion to a robot arm with redundant degrees of freedom, it is necessary to teach not only the position and orientation of the hand but also the robot's self-shape. Difficult to operate. However, for example, if compensation such as gravity is performed with the target joint torque Ft in the above-described impedance control and the position error torque F1max is set to zero, the entire robot arm can be arbitrarily deformed by external force, so a special input device Without a person, it is possible to directly grasp the robot arm link by hand and apply force to directly change the hand arm position / posture and the self-shape of the robot arm to teach the operation.

  Further, in the configuration of the robot arm 61, at least the three rotation axes (62, 63, 64) of the shoulder device among the rotation joints other than the wrist device have the rotation axes (62, 64) at both ends as shown in FIG. If the configuration is such that the joint device 1 can rotate infinitely, the hand position, the hand posture, and the self-shape can be arbitrarily and continuously changed while adapting to the external force except for the specific posture. It is also possible to repeat the turning operation as shown in (a), (b), (c), (d), or the reverse turning operation indefinitely. Such characteristics can be obtained without necessarily making all the joints capable of infinite rotation. In the robot arm 61, the shaft 63 has a configuration in which the rotation angle is limited from the viewpoint of structural strength and the like.

  Further, when a robot arm is configured by connecting joints, when the two joint devices 1 are connected at the fixed end side of the local controller as shown in FIG. As shown in FIG. 8B, one of the joint devices 1 is assigned to the other joint device 1 as shown in FIG. 8B, and the joint device 1 itself does not have a local controller. Can be replaced by '. In addition, as in the joint device 63 of the robot arm 61 in FIG. 6, a rotary joint with a limited rotation angle does not require a slip ring, and control processing can be left to a nearby local controller. As described above, the joint device 1 ″ having neither a slip ring nor a local controller can be configured, and a number of such joint devices 1 ″ can be connected in the vicinity of the joint device 1 to form a robot arm.

In non-manufacturing industry fields including daily life fields that come into contact with humans, the present invention can be applied to robots for safely performing various and complex tasks on behalf of human hands.

The block diagram which shows the structure of the rotary joint apparatus of this invention. Sectional drawing which shows the structure of the rotary joint apparatus of this invention. The block diagram which shows the structure of the robot arm of this invention. The perspective view of the wrist apparatus of this invention. The figure which shows a position error compensation torque. The perspective view of the 7 degree-of-freedom robot arm of this invention. The perspective view which shows the continuous self-deformability of the redundant freedom degree robot arm of this invention. The figure which illustrates the case where two joint apparatuses are connected by the edge part side fixed of the local controller. The block diagram which shows the structure of the robot arm of this invention different from FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Joint apparatus 2 DC motor 3 Wave generator 4 Flex spline 5 Circular spline 6 Encoder 7 Strain gauge 8 Local controller 9a, 9b, 9c Power supply line 10a, 10b, 10c Communication line 11 Pre-stage link 12 Post-stage link 17 Current collection ring 18 Brush 41 Wrist device 61 Robot arm

Claims (7)

In a robot arm in which a plurality of rotary joint devices for driving two links that are rotatably connected are connected ,
A local controller that locally controls the operation of the rotary joint device, and a master controller capable of transmitting and receiving data by communication via a communication line with the local controller,
The rotary joint device, the the angle detector and a torque detector and an actuator and a local controller, while based on the obtained value of angle and torque from said angle detector and said torque detector, said master controller In order to simultaneously realize control related to each characteristic of position, torque, rigidity, and viscosity instructed from the control command from the local controller to the actuator on the local controller,
The local controller obtains a torque value from the torque detector, thereby processing the control to adapt to the external force acting on the robot arm in a closed form on the local controller, and
The rotary joint device includes a slip ring mechanism that maintains an electrical connection between links while sliding along with the rotation of the joint, thereby enabling infinite rotation while maintaining an electrical connection between the links. robot arm, characterized. The rotation of the robot arm according to claim 1, wherein an electric motor and a speed reducer that decelerates the number of rotations of the electric motor are used as the actuator , and a strain sensor installed in the speed reducer is used as the torque detector. Joint device. The local controller with one of the two rotary joint device, shared by the other rotary joint device, according to the two rotary joint device to claim 1 which is connected at the end side that is fixed in the local controller Robot arm. The said other rotation joint apparatus is a rotation joint apparatus with a restriction | limiting in the rotation angle which does not require a slip ring , The process of the control was left to the local controller with which said one rotation joint apparatus was provided. Robot arm. The three rotary joint device is with respect to the axis of rotation of the intermediate rotary joint device in a rotating axis orthogonal to each other of the adjoining rotary joint device, and the rotation axis of the two ends of the rotary joint device is separated from each other plane The robot arm according to claim 1, wherein the robot arm is configured to be connected so as to rotate and to electrically connect three rotary joint devices in order. Said three a redundant degree of freedom structure having a rotating joint device for more than four axes other than the rotational joint device, according to claim 5 wherein the 4 or more axes of the rotary joint device comprising at least angle detector and a torque detector actuator of the robot arm. Three of the rotating joint device, with respect to the axis of rotation of the intermediate rotary joint device in a rotating axis orthogonal to each other of the adjoining rotary joint device, and the rotation axis of the two ends of the rotary joint device is separated from each other plane And a wrist device composed of three rotational joint devices electrically connected in order, a shoulder device composed of three rotational joint devices, and an elbow composed of one rotational joint device. A 7-degree-of-freedom redundant robot arm consisting of a device,
Said four rotary joint device in the shoulder unit and the elbow device and an actuator at least the angle detector and a torque detector,
The axis of rotation of all seven rotary joint device comprising three rotary joint device of the wrist device is connected so as to be perpendicular to each other and the rotation axis of the rotary joint device that is adjacent,
Robot arm according to claim 1, rotary joint device at both ends of the at least the shoulder device has the same configuration as the rotary joint device of the wrist device in addition to three rotational joint device of the wrist device.