A variable stiffness ball joint device based on particle jamming

Abstract

The application discloses a variable stiffness ball joint device based on particle blocking and relates to the technical field of robots, which comprises upper blocking air bags, a ball shell and lower blocking air bags arranged in sequence from top to bottom, the ball shell is internally provided with a ball groove, the ball groove is internally provided with a ball, the top of the ball is provided with an upper ball rod matched with the inner cylindrical surface of the upper blocking air bag, and the bottom of the ball is provided with a lower ball rod matched with the inner cylindrical surface of the lower blocking air bag. Through the arrangement, the upper blocking air bag and the lower blocking air bag are used as flexible elements to realize the variable stiffness of the ball hinge joint, the wall of the upper blocking air bag and the lower blocking air bag is designed in a bellows shape, the folding direction of the bellows is matched with the direction of the deformation of the ball hinge, and thus the initial stiffness of the air bag itself is reduced.

Description

Technical Field

[0001] The present invention relates to the field of robotics technology, and in particular to a variable-rigidity ball joint device based on particle blocking. Background Art

[0002] Humanoid robots are one of the most active branches of robotics. Joints are the most crucial component of a humanoid robot's mechanical structure. Their structure and performance directly impact the robot's overall performance, including maneuverability, operability, and smoothness. The ball-and-socket joint is a crucial component in robots. Existing ball-and-socket joints are rigid components with fixed stiffness, making them susceptible to damage when subjected to significant external forces. Summary of the Invention

[0003] The purpose of the present invention is to solve the defects in the prior art and to propose a variable stiffness ball joint device based on particle blocking.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A variable stiffness ball joint device based on particle blocking includes an upper blocking airbag, a spherical shell and a lower blocking airbag arranged in sequence from top to bottom, a ball groove provided in the spherical shell, a sphere provided in the ball groove, an upper ball rod provided on the top of the sphere to cooperate with the inner cylindrical surface of the upper blocking airbag, and a lower ball rod provided on the bottom to cooperate with the inner cylindrical surface of the lower blocking airbag.

[0006] Furthermore, a cylindrical hole is provided at the center of the upper blocking airbag, the cylindrical hole wall forms an inner cylindrical surface, the outer side of the inner cylindrical surface forms an outer bag wall of a bellows structure, the bottom of the inner cylindrical surface is an outer conical surface, and the inner side of the outer conical surface forms an inner bag wall of a bellows structure.

[0007] Furthermore, the spherical shell includes an upper spherical shell and a lower spherical shell. The upper end surface of the upper spherical shell is a conical structure that is compatible with the lower end surface of the upper blocking airbag. The lower end surface of the upper spherical shell is a planar structure that is compatible with the upper end surface of the lower spherical shell. The middle part of the lower part of the lower spherical shell is a truncated cone structure surrounded by a circular ring structure, and is compatible with the upper end surface of the lower blocking airbag.

[0008] Furthermore, the lower blocking airbag includes a spiral outer wall and a cylindrical hole, the cylindrical hole is used to cooperate with the lower club, and an S-shaped dividing wall is provided in the cavity inside the lower blocking airbag, the S-shaped dividing wall is used to separate the cavity, and a hole is opened on the S-shaped dividing wall.

[0009] Furthermore, the upper blocking airbag and the lower blocking airbag are both filled with hard particles.

[0010] Furthermore, both the upper blocking airbag and the lower blocking airbag are provided with air nozzles.

[0011] Beneficial effects

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The variable stiffness ball joint device mentioned in the present invention realizes active control of rotational stiffness based on the particle blocking principle, and realizes multi-medium mixed variable stiffness of a combination of fluid and solid. Its stiffness variation range is wide and the implementation method is simple and reliable;

[0014] (2) The upper blocking airbag and the lower blocking airbag work together to not only achieve the negative pressure stiffness change effect mentioned in the present invention, but also actively adjust the posture and position of the ball joint when positive and negative pressure are applied to each other, providing a desirable reference solution for the design of actively driven variable stiffness ball joints;

[0015] (3) The synergistic effect of the upper and lower blocking airbags can achieve a control effect of mutual antagonism between the upper and lower parts. From the perspective of balanced force, the ball joint can withstand a certain degree of external impact and maintain its posture unchanged, thereby improving the stability of the variable stiffness joint. Moreover, the high stiffness state of the mutually antagonistic combined variable stiffness components is far superior to the effect of a single airbag, greatly improving the variable stiffness range of the variable stiffness ball joint.

[0016] (4) The inner cylindrical surface of the upper blocking airbag is fixed to the ball rod, and the outer conical surface is fixed to the upper spherical shell. The middle airbag wall is a bellows structure, and its folding direction is along the spherical surface of the ball joint. Its design concept fully refers to the rotation direction of the ball joint around the Y axis and the Z axis. This can increase the deformation space of the airbag wall from a structural perspective, reduce deformation stress, and thus greatly reduce the initial stiffness of the ball joint;

[0017] (5) The upper and lower blocking airbags achieve stiffness changes by means of vacuum negative pressure, which can ensure that the stiffness is changed without changing the posture of the components at both ends of the ball joint, and will not generate additional interference forces on the connecting components at both ends of the joint;

[0018] (6) The upper blocking airbag and the lower blocking airbag are filled with positive pressure to enable the ball joint to drive the sole of the foot to return to its initial position. The implementation method is simple and reliable, and no additional return elements such as springs are required. While ensuring the recovery effect, the complexity of the robot leg structure is reduced, which is more conducive to the miniaturization of the entire robot.

[0019] (7) The outer wall of the lower blocking airbag is stretched along a spiral line around the outer cylindrical surface of the airbag. Compared with a conventional circular bellows, it has a certain degree of guidance for deformation in the direction of the central axis of the outer cylindrical surface of the airbag after being subjected to force (equivalent to increasing the load arm). Therefore, the outer wall deforms more and has lower stress after being subjected to force, and its initial stiffness is lower, and the overall stiffness change effect of the airbag is better.

[0020] (8) The initial stiffness of the lower blocking airbag is relatively low. Therefore, in the initial state, as long as there is a relatively low air pressure in the airbag, the particles in the airbag can be separated to achieve any deformation of the airbag (i.e., the low stiffness requirement of the ball joint is met). Therefore, in comparison, the ball joint has lower requirements for the pneumatic system equipped on the robot body, which is of great benefit to the miniaturization of the robot body.

[0021] (9) For the lower blocking balloon, the outer balloon wall mainly changes the stiffness of the ball joint around the Y and Z axes, and the S-shaped partition balloon wall mainly changes the stiffness of the ball joint around the X axis. The three-way composite structure allows the ball joint to rotate in a wider range of space.

[0022] (10) The S-shaped partition wall inside the lower blocking airbag can adjust the stiffness of the ball joint when rotating clockwise and counterclockwise around the X-axis, and evenly divide the inner cavity of the airbag into four equal parts, which can greatly improve the problem of uneven distribution of hard particles in the airbag after the ball joint is restored, which leads to uneven initial stiffness distribution after the ball joint is restored, which is a problem encountered in conventional bellows.

[0023] (11) Small holes are evenly arranged in a regular pattern on the wall of the S-shaped partition. On the one hand, this ensures that the air paths between the various partitioned chambers of the blocking airbag are connected, so that there is no need to set up a separate connecting air path inside the airbag, which greatly simplifies the air path design of the airbag. On the other hand, the mesh structure after the holes are opened can also greatly reduce the initial stiffness of the blocking airbag, thereby improving the variable stiffness effect of the blocking airbag.

[0024] (12) The outer wall of the lower blocking airbag is a specific spiral structure, which can be twisted around the X-axis under positive pressure. The greater the pressure, the greater the twist angle. This active twisting effect can be used for active drive and posture adjustment of the robot joint, which has great guiding significance for the development of active modular robot joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0026] Figure 1 Schematic diagram of the variable stiffness ball joint coordinate system (front view).

[0027] Figure 2 Schematic diagram of the variable stiffness ball joint coordinate system (top view).

[0028] Figure 3 Axonometric view of a variable stiffness ball joint.

[0029] Figure 4 This is the exploded diagram of the variable stiffness ball joint.

[0030] Figure 5 Cross-sectional view of a variable stiffness ball joint.

[0031] Figure 6 This is an axonometric view of the upper blocking airbag.

[0032] Figure 7 It is a cross-sectional view of the upper blocking airbag (schematic diagram of the folding direction of the bellows).

[0033] Figure 8 This is an axonometric view of the lower blocking airbag.

[0034] Figure 9 This is a cross-sectional view of the lower blocking airbag (middle cross-sectional view).

[0035] Figure 10 This is a cross-sectional view of the lower blocking airbag (middle longitudinal section).

[0036] In the figure: ball joint supporting parts - 1, upper blocking airbag - 2, lower blocking airbag - 3, upper ball shell - 11, lower ball shell - 12, ball rod - 13, upper ball rod - 131, sphere - 132, lower ball rod - 133, first inner cylindrical surface - 21, outer conical surface - 22, inner ball wall - 23, outer ball wall - 24, spiral outer ball wall - 31, upper flat bottom - 32, conical top surface - 33, lower bottom surface - 34, S-shaped segmented ball wall - 35, second inner cylindrical surface - 36, air nozzle - 37, sub-cavity - 38. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0038] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0039] Reference Figures 1-10 (1) The ball joint supporting parts 1 mainly include the upper ball shell 11, the lower ball shell 12, and the ball rod 13

[0040] The upper end surface of the upper spherical shell 11 is a conical surface for being fixedly connected to the outer conical surface of the upper blocking airbag, and the lower end surface of the lower spherical shell 12 is a circular plane for being fixedly connected to the upper bottom surface of the lower blocking airbag;

[0041] The club 13 includes an upper club 131, a ball 132, and a lower club 133. The upper club is fixedly connected to the inner cylindrical surface of the upper blocking airbag. The ball is detachably mounted between the upper and lower spherical shells, and together they constitute the basic kinematic pair of the ball joint. The lower club is fixedly connected to the inner cylindrical surface of the lower blocking airbag and the calf rod; the sole of the foot is fixedly connected to the mounting blocks on the upper and lower spherical shells.

[0042] (2) The upper blocking airbag 2, as a flexible element in the ball joint, can realize active control of its own stiffness. The first cylindrical surface 21 in the airbag is fixedly connected to the ball rod, and the outer conical surface 22 is fixedly connected to the upper spherical shell. The airbag walls between the inner cylindrical surface and the outer conical surface (inner airbag wall 23, outer airbag wall 24) are both bellows structures. The folding direction of the bellows structure of the outer airbag wall of the upper blocking airbag is along the spherical arc of the ball joint ball, so as to reduce the rotational stiffness of the ball joint around the Y axis and the Z axis. The low stiffness state of the ball joint around the X axis is mainly guaranteed by the deformation component of the bellows in the rotation direction around the Y axis and the Z axis and the flexibility of the material itself.

[0043] The upper blocking airbag is filled with hard particles approximately 0.5mm in diameter. When the upper blocking airbag is under a positive pressure greater than 30kPa, the airbag expands slightly, loosening the hard particles. When the ball joint is subjected to external force, the airbag's expansion force becomes the bearing capacity. The ball joint's stiffness is primarily affected by the positive pressure in the upper blocking airbag, at which point the ball joint is in a low-stiffness state. After the ball joint has rotated and deformed to a certain extent, the airbag is evacuated. The upper blocking airbag's main shape and posture remain unchanged, maintaining the relative position of the shell and the ball. The hard particles inside squeeze against each other, and the friction between the hard particles and their own rigidity work together to resist the external load on the ball joint. At this point, the ball joint barely deforms under the load, maintaining a high-stiffness state. Once the ball joint has completed its deformation, simply pressurizing the airbag with a positive pressure greater than 50kPa returns the ball joint to its original position.

[0044] (3) The lower blocking airbag 3 mainly includes a spiral outer wall 31, an upper flat bottom 32, a conical top surface 33, a lower bottom surface 34, an S-shaped segmented airbag wall 35, a second inner cylindrical surface 36, an air nozzle 37, and four circumferentially equidistantly arranged sub-cavities 38;

[0045] The upper bottom surface of the blocking airbag is divided into two parts. The upper flat bottom is glued to the upper spherical shell. The conical top surface is set inside. On the one hand, it can reduce the rotational stiffness of the blocking airbag itself around the Y-axis and Z-axis. On the other hand, it facilitates the positioning of the connection surface between the upper spherical shell and the blocking airbag, and prevents excessive glue from flowing into the ball joint matching area during gluing.

[0046] The lower blocking airbag is a flexible element in the variable-stiffness ball joint. Its function is to vary the overall rotational stiffness of the ball joint by actively changing its own stiffness. Installed between the lower ball shell and the calf bar, the lower blocking airbag has its upper flat bottom glued to the upper ball shell, and its inner cylindrical surface glued to the main ball joint bar (connecting the main ball joint shell and the main ball, acting as a flexible element between the shell and the ball during relative motion). This allows for three-way rotational stiffness control between the ball and shell.

[0047] The spiral bladder wall is a folded bellows structure. The direction of stretching of the bellows section is the spiral line around the outer cylindrical surface of the lower blocking airbag. After the outer bladder wall is compressed, the spiral line has a certain guiding effect on its deformation direction, thereby extending the local deformation of the blocking airbag under a slight positive pressure to the entire outer bladder wall (from the perspective of force analysis, it is equivalent to increasing the load arm), greatly reducing the initial stiffness of the variable stiffness ball joint around the Y-axis and Z-axis.

[0048] The S-shaped partition wall located inside the lower blocking airbag primarily functions to adjust the stiffness of the ball joint's rotation around the X-axis (the S-shaped structure ensures that the stiffness of the ball joint can be adjusted both clockwise and counterclockwise around the X-axis). The S-shaped partition wall divides the interior of the ball joint blocking airbag into four equally spaced chambers, significantly improving the uneven distribution of hard particles within the airbag after the ball joint returns to its original position, a problem often encountered with single-chamber bellows. Regularly spaced small holes are evenly distributed throughout the S-shaped partition wall (the size of the holes should be similar to or smaller than the size of the hard particles being filled). This ensures that the air paths between the various compartments of the blocking airbag are interconnected, eliminating the need for a separate connecting air path within the airbag, greatly simplifying the air path design. Furthermore, the resulting mesh structure significantly reduces the initial stiffness of the blocking airbag, improving the variable stiffness of the blocking airbag.

[0049] The working principle and use process of the present invention:

[0050] In the initial state, the airbag is under positive pressure, and the lower blocking airbag cavity is under a positive pressure of 5-15 kPa. The airbag expands slightly, and the hard particles inside are in a loose state. The friction between the particles is very small. In this way, the S-shaped partition walls can produce arbitrary deformation, and the inner cylindrical surface of the blocking airbag connected by the S-shaped partition walls and the outer airbag wall can produce relative rotation. That is, the rotational stiffness of the ball joint along the X-axis is low.

[0051] After the sole of the foot rotates to a certain extent, the flexible ball joint is deformed. At this time, negative pressure is input into the ball joint. The blocking airbag shrinks while the ball joint maintains its deformed shape (that is, the sole of the foot maintains its original posture). The hard particles in the airbag are squeezed against each other, and the friction between the particles resists the external force on the ball joint. At this time, the outer wall of the lower blocking airbag and the S-shaped partition wall are difficult to deform, that is, the three-way rotational stiffness of the ball joint is greatly enhanced.

[0052] The blocked airbag returns to its original position by injecting a positive pressure greater than 50Kpa into the airbag. At this time, the airbag expands and the hard particles inside return to their original position.

[0053] The folding direction of the bellows structure of the outer wall of the upper blocking airbag is along the spherical arc of the ball joint to reduce the rotational stiffness of the ball joint around the Y and Z axes. The low stiffness state of the ball joint around the X axis is mainly guaranteed by the deformation component of the bellows in the direction of rotation around the X axis and the flexibility of the material itself.

[0054] The outer wall of the lower blocking airbag is a folded, bellows-like structure. The bellows' cross-section stretches in a helical line around the club's cylindrical surface. This structure guides the outer wall's deformation when the upper and lower cylindrical surfaces of the blocking airbag are subjected to force, resulting in a lower initial stiffness and a reduced rotational stiffness around the Y and Z axes of the variable-stiffness ball joint. The S-shaped separator walls within the blocking airbag primarily alter the ball joint's rotational stiffness around the X axis. The four S-shaped separator walls, arranged equidistantly around the circumference, separate the hard particles within the blocking airbag, mitigating, to a certain extent, the problem of incomplete return of hard particles after significant deformation, leading to uneven distribution within the blocking airbag.

[0055] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A variable stiffness ball joint device based on particle blocking, characterized in that: The spherical body is provided with an upper blocking airbag, a spherical shell and a lower blocking airbag arranged in sequence from top to bottom, the spherical shell is provided with a ball groove, the ball is provided in the ball groove, the top of the sphere is provided with an upper ball rod which cooperates with the inner cylindrical surface of the upper blocking airbag, and the bottom is provided with a lower ball rod which cooperates with the inner cylindrical surface of the lower blocking airbag; the bottom of the inner cylindrical surface is an outer conical surface, and the inner side of the outer conical surface forms an inner airbag wall with a bellows structure; the spherical shell includes an upper spherical shell and a lower spherical shell, the upper end surface of the upper spherical shell is a conical surface structure which is adapted to the lower end surface of the upper blocking airbag, and the lower side of the lower spherical shell is adapted to the upper end surface of the lower blocking airbag; the lower blocking airbag includes a spiral outer airbag wall and a cylindrical hole, the cylindrical hole is used to cooperate with the lower ball rod, and an S-shaped dividing airbag wall is provided in the cavity inside the lower blocking airbag, the S-shaped dividing airbag wall is used to separate the cavity, and a hole is opened on the S-shaped dividing airbag wall; the interiors of the upper and lower blocking airbags are both filled with hard particles.

2. A variable stiffness ball joint device based on particle blocking according to claim 1, characterized in that: A through cylindrical hole is provided at the center of the upper blocking airbag, the cylindrical hole wall forms an inner cylindrical surface, and the outer side of the inner cylindrical surface forms an outer bag wall of a bellows structure.

3. The variable stiffness ball joint device based on particle blocking according to claim 1, characterized in that: The lower end surface of the upper spherical shell is a plane structure that matches the upper end surface of the lower spherical shell. The middle part below the lower spherical shell is a truncated cone structure surrounded by a circular ring structure.

4. The variable stiffness ball joint device based on particle blocking according to claim 1, characterized in that: The upper blocking airbag and the lower blocking airbag are both provided with air nozzles.

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