Variable stiffness robot wrist device

Abstract

The present invention relates to a variable stiffness robot wrist device comprising: a base unit; a fixing unit disposed on the upper portion of the base unit and including a plurality of actuators; a central unit disposed on the upper portion of the fixing unit and including a socket unit formed on the upper portion thereof; a movable unit including a ball joint extending downward, the ball joint being inserted in and supported by the socket unit and thus supported by the central unit; and an elastic member of which the inner circumference is coupled to the central unit around the central unit and the outer circumference is coupled to the outer circumference of the movable unit, wherein the movable unit can be tilted with respect to the central unit according to the rotation of the ball joint, and includes a plurality of connection units respectively connected to the fixing unit through wires respectively connected to the plurality of actuators.

Description

Variable stiffness robotic wrist device

[0001] This invention was made possible with the support of the National Research and Development Support Project [Project Unique Number: 1711168929, Project Number: 2020R1A2C2100193, Research Project Title: Development of a Shape and Flexibility Adaptive Robot Hand for Objects Based on Tactile / Variable Stiffness Palm Sensors] supported by the National Research Foundation of Korea, Ministry of Science and ICT.

[0002] The present invention relates to a variable stiffness robot wrist device, and more particularly, to a variable stiffness robot wrist device that can be changed into a rigidity mode in which the rigidity of the robot wrist is fixed by adjusting the tension of a wire, and a compliance mode in which the rigidity is removed and the robot wrist can comply with an external force.

[0003] Cross-reference to related applications

[0004] This application claims priority to Republic of Korea Patent Application No. 10-2024-0044771, filed April 2, 2024, the entire contents of which are incorporated herein by reference.

[0005] Currently, most robotic systems consisting of a robot manipulator and an end effector (e.g., a gripper or a hand) are widely used in various industrial fields, and these robotic systems operate by interacting with the environment based on physical contact in various fields.

[0006] For the interaction between these robots and the environment, for example, tactile sensors mounted on the robot can be used to detect external forces and provide feedback, or force or torque sensor-based control algorithms can be used to apply them to the field of physical interaction.

[0007] However, rigid robots that apply interaction by applying force or torque sensor-based control algorithms require very complex designs and have difficulty providing stable interaction that can respond to unexpected collisions or contacts.

[0008] Meanwhile, in order to supplement the stable interaction described above, methods are being used to control the stiffness of the robot wrist device by using a flexible material for the robot body, or by utilizing a variable stiffness actuator or a series of elastic structures.

[0009] However, conventional robotic wrist devices have limitations in application to various systems because the volume of the manipulator and end effector system is very large and the functions are limited due to structural rigidity.

[0010] For example, while a robotic wrist device with structural rigidity allows for precise manipulation, it has the disadvantage of being difficult to flexibly adapt to unstructured external environments. Conversely, a robotic wrist device with low rigidity can flexibly adapt to external environments, but its precision manipulation capabilities are limited.

[0011] Therefore, it is necessary to develop a device that can selectively change its stiffness while being flexible in operations where the force applied to the object changes depending on the stage of operation, as well as in operations where the robot simply maintains a constant force to contact the surface of the object to be worked on.

[0012] In order to achieve the above-described technical problem, the present invention can provide a variable stiffness robot wrist device including: a base portion; a fixed portion disposed on an upper portion of the base portion and including a plurality of actuators; a central portion disposed on an upper portion of the fixed portion and including a socket portion formed in an upper portion; a movable portion including a ball joint extending downward, the ball joint being inserted and supported in the socket portion and supported by the central portion; and an elastic member having an inner circumference joined to the central portion around the central portion and an outer circumference joined to the outer circumference of the movable portion; wherein the movable portion is capable of tilting relative to the central portion according to rotation of the ball joint, and the movable portion includes a plurality of connecting portions each connected to the fixed portion via wires each connected to a plurality of actuators.

[0013] In addition, the elastic member of the present invention may employ a circular diaphragm spring, and the diaphragm spring may include an inner rim coupled to a central portion; an outer rim coupled to an outer peripheral portion of a movable portion; and a sheet disposed between the inner rim and the outer rim.

[0014] Additionally, a plurality of slits may be formed in the sheet of the diaphragm spring of the present invention, which are arranged concentrically with the inner rim and the outer rim.

[0015] Additionally, the position of the inner rim of the diaphragm spring is fixed, and the outer rim is movable in response to the movement of the outer periphery of the movable part.

[0016] In addition, the plurality of actuators of the present invention can be arranged at the same angular phase on the circumference of the fixed portion, and specifically, the plurality of actuators is three, and can be arranged at a 120° angle on the circumference of the fixed portion.

[0017] In addition, the ball joint of the present invention further includes a magnetic material, and the central portion further includes a circuit portion having a magnetic sensor, so that the magnetic sensor detects movement of the magnetic material as the movable portion is tilted, thereby detecting the rotation angle of the ball joint.

[0018] In addition, the plurality of actuators of the present invention can each apply tension to the wire to limit the tilting movement of the movable part.

[0019] In addition, the base portion of the present invention may further include a circuit portion that controls the driving of a plurality of actuators.

[0020] The present invention can provide a robot wrist device with variable stiffness that can fix the stiffness of the robot wrist to enable precise position manipulation, while also securing a compliance function by removing the stiffness of the robot wrist as needed.

[0021] In addition, the present invention can provide a robot wrist device in which the entire system can convert the rigidity mode according to the environment without a separate device in the form of an independent module.

[0022] FIG. 1a is a perspective view schematically showing the structural characteristics of a robot wrist device according to one embodiment of the present invention.

[0023] Figure 1b is a conceptual diagram schematically showing application of a robot wrist device according to one embodiment of the present invention to a robot.

[0024] Figure 2 is an exploded perspective view schematically showing a robot wrist device according to one embodiment of the present invention.

[0025] Figure 3 is a cross-sectional view of a robot wrist device according to one embodiment of the present invention.

[0026] Figure 4 is a bottom view of a movable part of a robot wrist device according to one embodiment of the present invention.

[0027] Figure 5 is a perspective view schematically showing a diaphragm spring according to one embodiment of the present invention.

[0028] Figure 6 is a conceptual diagram schematically showing the behavior of a diaphragm spring according to one embodiment of the present invention.

[0029] Figure 7 is a conceptual diagram showing the operational relationship of a diaphragm spring according to the behavior of a movable part according to one embodiment of the present invention.

[0030] Figure 8 is a conceptual diagram schematically showing an operating mode according to wire tension adjustment of a robot wrist device according to one embodiment of the present invention.

[0031] FIG. 9 is a conceptual diagram schematically illustrating a method for measuring the inclination of a movable part of a robot wrist device according to one embodiment of the present invention.

[0032] FIG. 10 is a perspective view schematically showing an actuator mounted on a robot wrist device according to one embodiment of the present invention.

[0033] FIG. 11 is a conceptual diagram schematically showing the behavior of a robot wrist device according to one embodiment of the present invention in (a) compliance mode and (b) rigid mode.

[0034] FIG. 12 is a photograph schematically showing the behavior of a robot hand using a robot wrist device according to one embodiment of the present invention.

[0035] Hereinafter, a variable stiffness robot wrist device according to the present invention will be described through a preferred embodiment of the present invention based on the attached drawings.

[0036] Before the explanation, in various embodiments, components having the same configuration will be described representatively in one embodiment using the same symbols, and in other embodiments, only different components will be described.

[0037] FIG. 1a is a perspective view schematically showing the structural characteristics of a robot wrist device according to one embodiment of the present invention, and FIG. 1b is a conceptual diagram schematically showing the application of the robot wrist device according to one embodiment of the present invention to a robot.

[0038] As illustrated in FIG. 1b, a robot wrist device (1) according to one embodiment of the present invention can be installed and applied between a robot manipulator and a robot hand (e.g., a gripper).

[0039] In addition, the robot wrist device (1) according to one embodiment of the present invention can be independently configured without additional components other than a power input device, and its size can be structurally minimized in consideration of the operating range and moment inertia of the robot hand.

[0040] Specifically, a robot wrist device (1) according to one embodiment of the present invention has a structure in which a fixed portion (20) is arranged on the upper portion of a base portion (10), a central portion (30) is arranged on the upper portion of the fixed portion (20), and a movable portion (50) is arranged on the upper portion of the central portion (30). The specific configuration and operational relationship of the base portion (10), the fixed portion (20), the central portion (30), and the movable portion (50) will be described later.

[0041] In addition, the robot wrist device (1) according to one embodiment of the present invention can have a robot hand mounted on the aforementioned movable part (50), and the aforementioned base part (10) can be coupled to a manipulator to perform the function of a robot wrist.

[0042] FIG. 2 is an exploded perspective view schematically showing a robot wrist device (1) according to one embodiment of the present invention, and FIG. 3 is a cross-sectional view of a robot wrist device (1) according to one embodiment of the present invention.

[0043] As shown in FIGS. 2 and 3, a robot wrist device (1) according to one embodiment of the present invention has a fixing part (20) arranged on the upper portion of a base part (10), and this fixing part (20) includes a plurality of actuators.

[0044] In addition, a central portion (30) is placed on the upper portion of the fixed portion (20), and a socket portion (31) having a concave shape facing upward is formed at the center of the central portion (30).

[0045] In addition, an elastic member (40) is arranged around the central part (30), the inner circumference of which is connected to the central part (30) and the outer circumference of which is connected to a movable part (50) to be described later, and the movable part (50) is arranged on top of the elastic member (40).

[0046] Figure 4 is a bottom view of a movable part (50) of a robot wrist device (1) according to one embodiment of the present invention.

[0047] As shown in Fig. 4, a ball joint (51) extending downward is formed at the center of the movable part (50), and this ball joint (51) is inserted and supported in the socket part (31) formed in the aforementioned central part (30), so that the movable part (50) can be supported by the central part (30).

[0048] In addition, since the ball joint (51) of the movable part (50) and the socket part (31) of the central part (30) have a spherical shape, the ball joint (51) can rotate inside the socket part (31) according to the movement of the robot hand (not shown), so that the movable part (50) can tilt relative to the central part (30).

[0049] In addition, the movable part (50) has a plurality of connecting parts (53) formed on its outer periphery, and these multiple connecting parts (53) can be connected to a plurality of actuators (21) formed on the fixed part (20) through wires (22), respectively. The connection between the connecting part (53) of the movable part (50) and the wire (22) can be made, for example, by a screw bolt assembly or by fixing a wire (22) knot to the connecting part (53) of the movable part (50) with an adhesive.

[0050] Figure 5 is a perspective view schematically showing a diaphragm spring, which is an elastic member (40) according to one embodiment of the present invention.

[0051] As illustrated in Fig. 5, the diaphragm spring may be formed of an inner rim (42) coupled with the aforementioned central portion (30), an outer rim (43) coupled with the outer periphery (52) of the movable portion (50), and a sheet (44) disposed between the inner rim (42) and the outer rim (43). The coupling between the outer periphery (52) of the movable portion (50) and the outer rim (43) may be accomplished, for example, through a screw bolt assembly.

[0052] Additionally, a plurality of slits (45) are formed in the sheet (44) and are arranged concentrically with the inner rim (42) and the outer rim (43).

[0053] FIG. 6 is a conceptual diagram schematically showing the behavior of a diaphragm spring according to one embodiment of the present invention, and FIG. 7 is a conceptual diagram showing the operational relationship of a diaphragm spring according to the behavior of a movable part (50) according to one embodiment of the present invention.

[0054] In one embodiment of the present invention, the position of the inner rim (42) of the diaphragm spring is fixed by being combined with the aforementioned central portion (30), and the outer rim (43) is movable in response to the movement of the outer peripheral portion (52) of the movable portion (50).

[0055] Specifically, by introducing the aforementioned elastic member (40) into the robot wrist device (1), the robot wrist device (1) can be made to move flexibly. Accordingly, the elastic member (40) according to one embodiment of the present invention is composed of a plate spring such as a diaphragm spring, and each has a shape in which they are symmetrically connected at 120° intervals in the circumferential direction.

[0056] In addition, the diaphragm spring according to one embodiment of the present invention may be composed of a polymer material (e.g., POM) that is lighter than a metal material, and it is preferable to use a material with a large elastic modulus to allow a large deflection.

[0057] In addition, the diaphragm spring according to one embodiment of the present invention can be easily manufactured as an integral body through plate-shaped laser cutting processing, and can reduce weight and assembly errors with other parts.

[0058] As described above, since the ball joint (51) of the movable part (50) is supported by the central part (30), the Z-axis movement of the diaphragm spring is restricted, and only angular movement in the X-axis and Y-axis is permitted, thereby restricting the undesired parasitic translation displacement of the movable part (50), thereby preventing the occurrence of tip motion when an external force is applied to the robot hand, and allowing the occurrence of a controllable tilt motion.

[0059] FIG. 9 is a conceptual diagram schematically illustrating a method for measuring the inclination of a movable part (50) of a robot wrist device (1) according to one embodiment of the present invention.

[0060] As illustrated in Fig. 9, the ball joint (51) of the movable part (50) may further include a magnetic material (511), and the central part (30) may include a circuit part (32) in which a magnetic sensor (33) is built in a position corresponding to the magnetic material (511). Accordingly, as the movable part (50) tilts, the magnetic sensor (33) detects a change in the magnetic field according to a change in the posture of the magnetic material (511), and thus the movement of the movable part (50) can be detected by detecting the rotation angle of the ball joint (51).

[0061] That is, since the magnetic material (511) and the magnetic sensor (33) are located close together, the change in magnetic flux density according to the change in the attitude of the magnetic material (511) can be sensitively measured while minimizing the effect of an external magnetic field.

[0062] FIG. 8 is a conceptual diagram schematically showing an operation mode according to tension adjustment of a wire (22) of a robot wrist device (1) according to one embodiment of the present invention, and FIG. 10 is a perspective view schematically showing an actuator (21) mounted on a robot wrist device (1) according to one embodiment of the present invention.

[0063] As illustrated in FIG. 10, a plurality of actuators (21) according to one embodiment of the present invention can be arranged at the same angle (θ) phase in the circumferential direction of the fixed part (20), and for example, when three actuators (21) are set, they can be arranged at an angle of 120° in the circumferential direction of the fixed part (20).

[0064] That is, by arranging three actuators (21) radially at the same angular phase, the robot wrist device (1) according to one embodiment of the present invention is capable of not only tilting motion but also conical motion that can rotate the robot hand around the robot wrist device (1), like a human wrist.

[0065] Specifically, the robot wrist device (1) according to one embodiment of the present invention can release or provide a certain rigidity to the robot wrist by releasing the wire (22) connected to each actuator (21) (22a, releasing the tension of the wire (22)) or by pulling the wire (22) (22b, adding tension to the wire (22)).

[0066] In addition, FIG. 11 is a conceptual diagram schematically showing the behavior of a robot wrist device (1) according to one embodiment of the present invention in (a) a compliance mode and (b) a rigid mode, and FIG. 12 is a photograph schematically showing the behavior of a robot wrist device (1) according to one embodiment of the present invention.

[0067] Specifically, when tension is applied to all wires (22), the movement of the movable part (50) is restricted, so that the robot wrist can be operated in a fixed rigidity mode that locks the movement. Conversely, when the tension of all wires (22) is released, the movable part (50) of the robot wrist device (1) can be operated in a compliant mode that allows it to passively respond to an external force.

[0068] Therefore, the robot wrist device (1) according to one embodiment of the present invention can be used as a robot wrist device with variable stiffness that can be changed between a rigid mode and a compliant mode.

[0069] Fig. 12 is a photograph schematically showing the behavior of a robot hand using a robot wrist device (1) according to one embodiment of the present invention.

[0070] Specifically, in the case where the rigidity is fixed as the rigid mode in the initial movement process (① in FIG. 12) of the robot wrist device (1) according to one embodiment of the present invention, as in ② in FIG. 12, even if the gripper, which is the robot hand, comes into contact with the ground, the movement of the gripper toward the ground is continuously performed while maintaining the rigidity of the robot wrist device (1). Thereafter, when the robot wrist device (1) is changed to the compliance mode, deformation occurs as the robot wrist device conforms to the ground, and the gripper can be positioned horizontally with the ground.

[0071] For example, in order to stably grip a flat object such as a coin, it is necessary to align the center line of the gripper with the line perpendicular to the surface of the object, but it is generally difficult to precisely manipulate the center line of the gripper, so as shown in ① of Fig. 12, it can be confirmed that the center lines of the manipulator and the gripper do not align with the line perpendicular to the surface of the object located on the table.

[0072] Accordingly, as shown in ② of Fig. 12, the position of the gripper on the surface is moved to match the line perpendicular to the surface of the object, and during this movement process, a single contact occurs between the gripper and the ground of the table.

[0073] Next, as illustrated in ③ of FIG. 12, when the robot wrist device (1) is in the compliance mode, the robot wrist device (1) is deformed due to the repulsive force of the ground due to the continuous position movement of the gripper, and as the gripper and the ground come into multiple contact, the movement of the gripper is completed so that the vertical line of the coin plane perpendicular to the surface of the object and the center line of the robot and the gripper coincide. That is, through the compliance mode of the robot wrist device (1) according to one embodiment of the present invention, the robot wrist can be deformed into a desired posture while complying with an external force until the position of the gripper is determined.

[0074] Next, as shown in ④ of Fig. 12, after the gripper has gripped an object in a compliant state of the robot wrist device (1), the gripper is moved as shown in ⑤ of Fig. 12. In particular, since the posture and position of the manipulator and the gripper after gripping the object must be fixed, it is necessary to switch the robot wrist device (1) from the compliant mode to the rigid mode. In addition, since the inclination of the movable part (50) can be accurately measured through the magnetic sensor (33) built into the central part (30), the operation value of the actuator (21) can be accurately calculated to fix the rigid mode of the robot wrist device (1).

[0075] Finally, as shown in ⑥ of Fig. 12, even if the contact between the gripper and the ground is removed, it can be confirmed that the object is lifted while the center line of the gripper is maintained perpendicular to the ground of the table because the robot wrist device (1) is switched to the rigid mode in the process of ⑤ of Fig. 12.

[0076] Therefore, by using a robot wrist device (1) having variable stiffness according to one embodiment of the present invention, it can be advantageous to grasp a flat object such as a coin, and after grasping the object, the robot wrist device (1) that has completed adaptation is switched back to a rigid mode with the rigidity fixed, as shown in ④ of Fig. 12, so that stable gripping of the gripper can be maintained, and an accurate posture of the gripper can be maintained.

[0077] That is, it was confirmed that the robot wrist device (1) according to one embodiment of the present invention can have variable stiffness, so that it is advantageous in adapting to a difficult environment based on the flexibility of the compliance mode, and that it is capable of stable post-grabbing work based on the stiffness of the rigid mode.

[0078] By referring to the above description, those skilled in the art to which the present invention pertains will be able to understand that the present invention can be implemented in other specific forms without changing the technical idea or essential characteristics thereof.

[0079] Therefore, it should be understood that the embodiments described so far are exemplary in all respects and are not intended to limit the present invention to the embodiments described above, and the scope of the present invention is indicated by the claims described below rather than the detailed description described above, and all changes or modified forms derived from the meaning and scope of the claims and equivalent concepts should be interpreted as being included in the scope of the present invention.

[0080] According to the variable stiffness robot wrist device according to embodiments of the present invention, precise position manipulation is possible while ensuring compliance function, and the stiffness mode can be changed according to the environment without a separate device in the form of an independent module.

Claims

1. Base section; A fixed part disposed on the upper part of the base part and including a plurality of actuators; A central portion including a socket portion formed at the upper portion and disposed at the upper portion of the fixed portion; A movable part including a ball joint extending downward, wherein the ball joint is inserted and supported into the socket part and supported in the central part; and An elastic member is included, wherein the inner circumference is connected to the central portion around the central portion, and the outer circumference is connected to the outer circumference of the movable portion; The above movable part can tilt relative to the central part according to the rotation of the ball joint, A variable stiffness robot wrist device, characterized in that the movable part includes a plurality of connecting parts, each of which is connected to the fixed part via wires that are respectively connected to the plurality of actuators.

2. In paragraph 1, A variable stiffness robot wrist device characterized in that the above elastic member is a circular diaphragm spring.

3. In paragraph 2, A variable stiffness robot wrist device characterized in that the diaphragm spring includes an inner rim coupled to the central portion; an outer rim coupled to the outer peripheral portion of the movable portion; and a sheet disposed between the inner rim and the outer rim.

4. In paragraph 3, A variable stiffness robot wrist device characterized in that a plurality of slits are formed in the sheet and are arranged concentrically with the inner rim and the outer rim.

5. In paragraph 4, A variable stiffness robot wrist device characterized in that the position of the inner rim is fixed and the outer rim is movable in response to movement of the outer peripheral portion of the movable portion.

6. In paragraph 1, A variable stiffness robot wrist device, characterized in that the plurality of actuators are arranged with the same angular phase on the circumference of the fixed part.

7. In paragraph 6, A variable stiffness robot wrist device characterized in that the plurality of actuators are three and arranged at a 120° angle around the circumference of the fixed part.

8. In paragraph 1, The above ball joint further includes a magnetic material, The central portion further includes a circuit portion having a magnetic sensor, A variable stiffness robot wrist device characterized in that the magnetic sensor detects the movement of the magnetic material according to the inclination of the movable part, thereby detecting the rotation angle of the ball joint.

9. In paragraph 1, A variable stiffness robot wrist device, characterized in that the plurality of actuators can each apply tension to the wire to limit the tilting movement of the movable part.

10. In paragraph 1, A variable stiffness robot wrist device, characterized in that the base portion further includes a circuit portion that controls the operation of the plurality of actuators.

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