Spatial two-rotation and one-movement three-degree-of-freedom parallel mechanism and mechanical device

Abstract

The invention provides a spatial two-rotation and one-movement three-degree-of-freedom parallel mechanism. The spatial two-rotation and one-movement three-degree-of-freedom parallel mechanism comprises a fixed platform, a movable platform and three main branch chains. Each main branch chain supports the movable platform to realize two-rotation and one-movement three-degree-of-freedom movement and comprises a first branch chain and a second branch chain; the first end of the first branch chain and the first end of the second branch chain are in spherical connection with the movable platform through equivalent spherical hinges, the second end of the first branch chain is rotationally connected with the fixed platform, and the second end of the second branch chain is rotationally connected with the fixed platform through a rotating pair. The parallel mechanism is high in bearing capacity, high in rigidity, high in fault-tolerant capability, high in reliability and high in stability, and stable supporting and stable movement of the movable platform can be achieved; spherical surface connection is achieved through equivalent spherical hinges, two-rotation and one-movement three-degree-of-freedom flexible movement is achieved only through a rotary hinge mode, and the parallel mechanism has the advantages of being large in working space, small in accumulative error, timely in motion response and high in motion output efficiency and precision.

Description

Technical Field

[0001] This disclosure relates to the field of parallel robots, and more specifically to a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space. Background Technology

[0002] Parallel robots possess advantages such as small cumulative error, high motion accuracy, and fast response speed, playing a crucial role in industrial production. Thanks to their excellent characteristics, low-degree-of-freedom parallel robots can be used in scenarios such as posture adjustment, precision manufacturing, and medical surgery. Spatial two-rotation-one-transfer parallel mechanisms are a very typical type of low-degree-of-freedom parallel mechanism. Due to their simple structure and ease of control, they have received widespread attention from academia and industry.

[0003] Existing parallel mechanisms consisting of two rotary axes and one linear actuator often suffer from structural asymmetry, insufficient rigidity, low load-bearing capacity, and low fault tolerance. In related technologies, parallel mechanisms with few degrees of freedom (two rotary axes and one linear actuator) frequently employ sliding pairs as the sliding drive pair. However, since the current power source is a rotary motor, additional linear mechanical structures such as linear slides or ball screws are needed to convert the motor's rotational motion into linear motion. This introduction of linear mechanical structures introduces a certain degree of dynamic response delay into the parallel structure, reducing the output efficiency and accuracy of the rotary motor. Therefore, friction and backlash in the sliding pairs become error sources in the two-rotor-one-linear actuator parallel mechanism, reducing its transmission accuracy and increasing its mechanical complexity, resulting in a more complex overall parallel structure.

[0004] The information disclosed in the Background section of this disclosure is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or any implication that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] In view of the above problems, this disclosure provides a three-degree-of-freedom parallel mechanism and mechanical device with two rotations and one transfer in space.

[0006] According to the first aspect of this disclosure, a three-degree-of-freedom parallel mechanism with two spatial rotations and one spatial transfer is provided, comprising:

[0007] Determine the platform;

[0008] Dynamic platform;

[0009] Three identical main branches support the moving platform in achieving three degrees of freedom motion. The three degrees of freedom motion includes two rotational motions about two skew axes in space, and one translational motion along the normal direction of the fixed platform. Each main branch includes a first branch and a second branch. The first end of the first branch and the first end of the second branch are connected to the spherical surface of the moving platform via an equivalent ball joint. The second end of the first branch is rotatably connected to the fixed platform, and the second end of the second branch is rotatably connected to the fixed platform via a revolute joint.

[0010] Each of the first branch chains includes;

[0011] The first upper connecting rod has its first end connected to the moving platform via the equivalent ball joint.

[0012] The first lower connecting rod has its first end rotatably connected to the second end of the first upper connecting rod via a first revolute joint, and the second end of the first lower connecting rod is rotatably connected to the fixed platform via a second revolute joint.

[0013] Each second branch chain includes:

[0014] The first end of the second upper link is connected to the first end of the first upper link and the moving platform respectively through the equivalent ball joint;

[0015] The first end of the second lower connecting rod is rotatably connected to the second end of the second upper connecting rod via a third revolute joint, and the second end of the second lower connecting rod is rotatably connected to the fixed platform via a fourth revolute joint.

[0016] According to embodiments of this disclosure, the equivalent ball joint includes:

[0017] A first rotating shaft is rotatably connected to the moving platform, and the rotation axis of the first rotating shaft is perpendicular to the moving platform;

[0018] The second rotating shaft is rotatably connected to the first rotating shaft, and the rotation axis of the second rotating shaft is perpendicular to the rotation axis of the first rotating shaft;

[0019] A third rotating shaft is rotatably connected to the second rotating shaft, and the rotation axis of the third rotating shaft is perpendicular to the rotation axis of the second rotating shaft and the axis of the first rotating shaft, respectively.

[0020] According to embodiments of this disclosure, the second revolute joint and the fourth revolute joint of each main branch are configured as follows:

[0021] The arrangement points of each of the second revolute joints are evenly distributed on the arc of the first circumcircle, and the axis of each of the second revolute joints is tangent to the first circumcircle; wherein, the first circumcircle is the circumcircle formed by the connection points of each of the second revolute joints and the fixed platform;

[0022] The arrangement points of each of the fourth revolute joints are evenly distributed on the arc of the second circumcircle, and the axis of each of the fourth revolute joints is tangent to the second circumcircle; wherein, the second circumcircle is the circumcircle formed by the connection points of each of the fourth revolute joints and the fixed platform;

[0023] The diameter of the first circumcircle is larger than the diameter of the second circumcircle.

[0024] According to embodiments of this disclosure, the axes of the first revolute joint, the second revolute joint, the third revolute joint, and the fourth revolute joint in each of the main branches are parallel to each other.

[0025] According to an embodiment of this disclosure, the arrangement points of each of the equivalent ball joints are evenly distributed on the arc of the third circumcircle of the moving platform; wherein, the third circumcircle is the circumcircle formed by the connection points of each of the equivalent ball joints and the moving platform.

[0026] According to embodiments of this disclosure, it further includes:

[0027] Six power sources are provided, each of which is connected to each of the second and fourth rotating joints. The power sources are used to drive the second and fourth rotating joints in each of the main branches, so that the first lower connecting rod and the second lower connecting rod rotate relative to the fixed platform.

[0028] The two rotational motions about the two axes of the skew space, and the one translational motion along the normal of the fixed platform, include:

[0029] While the first lower connecting rod and the second lower connecting rod rotate relative to the fixed platform, they respectively drive the first upper connecting rod and the second upper connecting rod to rotate relative to the first lower connecting rod and the second lower connecting rod.

[0030] While the first upper link and the second upper link rotate relative to the first lower link and the second lower link, they drive the moving platform to perform spherical motion relative to the first upper link and the second upper link.

[0031] While the moving platform performs spherical motion relative to the first upper link and the second upper link, it also achieves two rotational motions around two axes of skew surfaces in space, and one translational motion along the normal of the fixed platform.

[0032] A second aspect of this disclosure provides a mechanical device comprising the three-degree-of-freedom parallel mechanism described above.

[0033] Beneficial effects

[0034] The three-degree-of-freedom parallel mechanism with two rotations and one transfer provided according to the embodiments of this disclosure has at least the following beneficial effects:

[0035] 1. The main branch is formed by the branch chains sharing the same ball joint. The three main branches form a spatial two-rotation-one-transfer parallel mechanism, which has a symmetrical structure, strong load-bearing capacity and high rigidity.

[0036] 2. The driving internal force is distributed in the form of multiple redundant branches, so that the internal force coupling that cancels the singular trend is actively generated inside the mechanism, realizing the stable support and smooth movement of the moving platform, and giving the two-rotation-one-transfer parallel mechanism strong fault tolerance, reliability and stability.

[0037] 3. By using an equivalent ball joint to achieve spherical connection, the sliding friction motion loss caused by the surface contact of traditional ball joints is avoided. Each branch chain has a simple structure and achieves flexible three-degree-of-freedom motion of two rotations and one transfer through rotational hinge. This makes the parallel mechanism simple in structure, large in working space, small in cumulative error, timely in motion response, and has high motion output efficiency and accuracy. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0040] Figure 1 A schematic diagram of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure is shown.

[0041] Figure 2 A perspective view of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure is shown schematically.

[0042] Figure 3 The schematic diagram illustrates an equivalent ball joint perspective view of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure;

[0043] Figure 4 The diagram schematically illustrates the arrangement of the second and fourth revolute joints of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure.

[0044] The meanings of the reference numerals in the above figures are as follows:

[0045] 100-Fixed Platform;

[0046] 110 - First circumcircle;

[0047] 120 - Second circumcircle;

[0048] 200-Dynamic Platform;

[0049] 300 - Main chain;

[0050] 311 - First upper connecting rod;

[0051] 312 - First lower linkage;

[0052] 313 - First rotating joint;

[0053] 314 - Second rotating joint;

[0054] 321 - Second upper link;

[0055] 322 - Second lower link;

[0056] 323 - Third rotating joint;

[0057] 324 - Fourth rotating joint;

[0058] 330-equivalent ball joint;

[0059] 331 - First pivot;

[0060] 332 - Second shaft;

[0061] 333 - Third pivot;

[0062] 400 - Power Source. Detailed Implementation

[0063] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0064] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0065] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0066] When using expressions such as "at least one of A, B, and C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). When using expressions such as "at least one of A, B, or C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0067] The embodiments of this disclosure provide a spatial two-rotation-one-transfer three-degree-of-freedom parallel mechanism. The main branches are formed by sharing the same ball joint, and the three main branches constitute the spatial two-rotation-one-transfer parallel mechanism. This mechanism is symmetrical, has high load-bearing capacity, and high stiffness. The multiple redundant branches can distribute the driving internal force, enabling the mechanism to actively generate internal force couplings that counteract singular trends, achieving stable support and smooth movement of the moving platform. This gives the two-rotation-one-transfer parallel mechanism strong fault tolerance, reliability, and stability. The spherical connection is achieved through an equivalent ball joint, avoiding the sliding friction motion loss caused by traditional ball joint surface contact. Each branch has a simple structure, achieving flexible three-degree-of-freedom movement through rotational hinges alone. This parallel mechanism features a simple structure, large working space, small cumulative error, timely motion response, and high motion output efficiency and accuracy.

[0068] Figure 1 The schematic diagram illustrates a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure.

[0069] According to embodiments of this disclosure, a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space is provided, such as... Figure 1As shown, the three-degree-of-freedom parallel mechanism includes a fixed platform 100, a moving platform 200, and three main branches 300 with identical structures. Each main branch 300 supports the moving platform 200 in achieving three-degree-of-freedom motion, which includes two rotational motions about two axes of different spatial planes and one translational motion along the normal direction of the fixed platform 100. Each main branch 300 includes a first branch chain and a second branch chain. The first end of the first branch chain and the first end of the second branch chain are spherically connected to the moving platform 200 via an equivalent ball joint 330. The second end of the first branch chain is rotatably connected to the fixed platform 100, and the second end of the second branch chain is rotatably connected to the fixed platform 100 via a revolute joint.

[0070] This three-degree-of-freedom parallel mechanism uses the same ball joint to form the main branch chain, and adopts three main branches to support the moving platform to achieve two rotations and one transfer motion in space. This three-degree-of-freedom parallel mechanism has the characteristics of structural symmetry, strong load-bearing capacity and high stiffness.

[0071] Each first branch of the above three-degree-of-freedom parallel mechanism includes: a first upper link 311 and a first lower link 312. The first end of the first upper link 311 is connected to the moving platform 200 via an equivalent ball joint 330. The first end of the first lower link 312 is rotatably connected to the second end of the first upper link 311 via a first revolute joint 313, and the second end of the first lower link 312 is rotatably connected to the fixed platform 100 via a second revolute joint 314.

[0072] Each second branch of the above three-degree-of-freedom parallel mechanism includes: a second upper link 321 and a second lower link 322. The first end of the second upper link 321 is connected to the first end of the first upper link 311 and the moving platform 200 via an equivalent ball joint 330. The first end of the second lower link 322 is rotatably connected to the second end of the second upper link 321 via a third revolute joint 323, and the second end of the second lower link 322 is rotatably connected to the fixed platform 100 via a fourth revolute joint 324.

[0073] Each branch includes only three kinematic pairs: two revolute joints and one equivalent ball joint, which minimizes the cumulative error and increases the accuracy of the motion output of the three-degree-of-freedom parallel mechanism. Furthermore, the three-degree-of-freedom parallel mechanism of this disclosure distributes the driving internal force of the mechanism through multiple redundant branches, enabling the mechanism to actively generate internal force couplings that counteract singular trends. This achieves stable support and smooth motion of the moving platform, giving the two-revolute-one-transfer parallel mechanism strong fault tolerance, reliability, and stability.

[0074] Figure 2 A perspective view of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure is shown schematically.

[0075] like Figure 1 and Figure 2 As shown, the axes of the first revolute joint 313, the second revolute joint 314, the third revolute joint 323, and the fourth revolute joint 324 in each main branch 300 are parallel to each other. The parallelism of the revolute joints of each main branch ensures that the internal force system of the three-degree-of-freedom parallel mechanism of this embodiment remains in a two-dimensional plane, avoiding the introduction of a three-dimensional force system by non-parallel axes, which would increase the load on the revolute joints and support structure, thereby increasing the load-bearing capacity of the three-degree-of-freedom parallel mechanism.

[0076] like Figure 2 As shown, the three-degree-of-freedom parallel mechanism of this embodiment further includes six power sources 400, such as rotary motors. Each power source 400 is connected to each of the second revolute joints 314 and the fourth revolute joint 324. The power sources 400 drive the second revolute joints 314 and the fourth revolute joints 324 in each main branch 300, causing the first lower connecting rod 312 and the second lower connecting rod 322 to rotate relative to the fixed platform 100. Each power source 400 provides power to the three-degree-of-freedom parallel mechanism of this embodiment, enabling the moving platform 200 to achieve two rotational movements about two axes in a spatially skewed plane and one translational movement along the normal direction of the fixed platform 100.

[0077] The above-described spatial rotation and translation motion is as follows: While the first lower connecting rod 312 and the second lower connecting rod 322 rotate relative to the fixed platform 100, they simultaneously drive the first upper connecting rod 311 and the second upper connecting rod 321 to rotate relative to the first lower connecting rod 312 and the second lower connecting rod 322, respectively. Simultaneously, the first upper connecting rod 311 and the second upper connecting rod 321 rotate relative to the first lower connecting rod 312 and the second lower connecting rod 322, driving the moving platform 200 to perform a spherical motion relative to the first upper connecting rod 311 and the second upper connecting rod 321. While the moving platform 200 performs this spherical motion relative to the first upper connecting rod 311 and the second upper connecting rod 321, it simultaneously achieves two rotational motions around two skew axes in space, and one translational motion along the normal direction of the fixed platform 100.

[0078] The embodiments disclosed herein use six power sources to drive the revolute joints of the three-degree-of-freedom parallel mechanism respectively. This redundant driving method improves the stiffness and load capacity of the three-degree-of-freedom parallel mechanism, while also enhancing its stability. When a drive joint of the mechanism malfunctions, or when one of the non-drive branches is damaged and unable to function, the corresponding redundant branch can take over the work of the faulty branch, further enhancing the fault tolerance and reliability of the three-degree-of-freedom parallel mechanism.

[0079] The three-degree-of-freedom parallel mechanism of this disclosure avoids the sliding drive method using sliding pairs in related technologies. Instead, it directly connects to and drives the rotary joints with a power source, eliminating the need for additional linear mechanical structures such as linear slides or ball screws. This converts the rotational motion of the rotary joints into the linear motion of the moving platform. The redundant rotational drive method of this disclosure avoids the additional mechanical complexity and power response delays caused by the introduction of linear mechanical structures in parallel mechanisms, thus improving the motion output efficiency and accuracy of the two-rotor-one-transfer parallel mechanism.

[0080] Figure 3 The diagram schematically illustrates an equivalent ball joint perspective view of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure.

[0081] like Figure 2 and Figure 3 As shown, the equivalent ball joint 330 includes: a first rotating shaft 331, a second rotating shaft 332, and a third rotating shaft 333. The first rotating shaft 331 is rotatably connected to the moving platform 200, and its rotation axis is perpendicular to the moving platform 200. The second rotating shaft 332 is rotatably connected to the first rotating shaft 331, and its rotation axis is perpendicular to the rotation axis of the first rotating shaft 331. The third rotating shaft 333 is rotatably connected to the second rotating shaft 332, and its rotation axis is perpendicular to both the rotation axis of the second rotating shaft 332 and the axis of the first rotating shaft 331.

[0082] By using an equivalent ball joint to achieve spherical connection, the sliding friction motion loss caused by the traditional ball joint surface contact can be avoided, making the structure of each branch chain simple. It can achieve flexible three-degree-of-freedom motion of two rotations and one transfer by simply using rotational hinge. This makes the parallel mechanism simple in structure, large in working space, small in cumulative error, timely in motion response, and improves the motion output efficiency and accuracy of the parallel mechanism.

[0083] Figure 4 The diagram schematically illustrates the arrangement of the second and fourth revolute joints of a three-degree-of-freedom parallel mechanism with two rotations and one transfer in space according to an embodiment of the present disclosure.

[0084] like Figure 1 , Figure 2 and Figure 4 As shown, the second revolute joints 314 of each main branch 300 are arranged such that the arrangement points of each second revolute joint 314 are evenly distributed on the arc of the first circumcircle 110, and the axis of each second revolute joint 314 is tangent to the first circumcircle 110. According to the embodiment of this disclosure, the first circumcircle 110 is the circumcircle formed by the connection points of each second revolute joint 314 and the fixed platform 100.

[0085] The fourth revolute joint 324 is arranged such that all the arrangement points of the fourth revolute joint 324 are evenly distributed on the arc of the second circumcircle 120, and the axis of each fourth revolute joint 324 is tangent to the second circumcircle 120. According to the embodiment of this disclosure, the second circumcircle 120 is the circumcircle formed by the connection points of all the fourth revolute joints 324 and the fixed platform 100. In this embodiment, the diameter of the first circumcircle 110 is larger than the diameter of the second circumcircle 120.

[0086] According to another embodiment of this disclosure, the arrangement points of all equivalent ball joints 330 can be evenly distributed on the arc of the third circumcircle of the moving platform 200; wherein, the third circumcircle is the circumcircle formed by the connection points of all equivalent ball joints 330 and the moving platform 200.

[0087] By arranging the second and fourth revolute joints of each main branch evenly, and by uniformly distributing the equivalent ball joints on the moving platform, uniform support of the fixed platform for the moving platform is achieved, further improving the stability and reliability of the two-rotation-one-transfer-three-degree-of-freedom parallel mechanism in space.

[0088] This disclosure also provides a mechanical device, including the above-described three-degree-of-freedom parallel mechanism with two rotations and one transfer in space.

[0089] To facilitate understanding of the above embodiments, a specific application scenario of the above embodiments will be used as an example for illustration below:

[0090] On a high-end five-axis linkage machining center, the three-degree-of-freedom parallel mechanism with two rotations and one translation in space disclosed herein is used to adjust the position and orientation of the blade profile of the integral titanium alloy bladed disk of an aero-engine in order to achieve precision milling.

[0091] In this embodiment, the blades of the impeller are complex spatial curved surfaces, and the material is difficult to machine. During machining, based on the preset dense tool position points, the system continuously calculates the precise pose required by the spindle unit (moving platform)—that is, the precise deflection and pitch around two axes (2R, i.e., two rotational motions), and the precise feed along the spindle direction (1T, i.e., one translational motion). Through the inverse kinematics model, the pose requirements of the above three degrees of freedom are quickly converted into precise rotational commands for six servo motors. The six drive systems work together under high-speed closed-loop control, enabling the spindle to produce sensitive and robust composite motion, ensuring that the ball end mill always maintains the optimal cutting posture and constant linear velocity along the surface normal.

[0092] Due to the narrow channels and drastic curvature changes between adjacent blades of the impeller, the toolpath may force the mechanism into the vicinity of theoretically singular configurations. For non-redundant mechanisms, this would pose a risk of sharp stiffness reduction and motion instability. However, the redundant drive and redundant branch structure of the three-degree-of-freedom parallel mechanism disclosed herein can "support" the entire architecture from within the parallel mechanism, maintaining high global stiffness and stability, ensuring a smooth cutting process with minimal chatter even under extreme orientations.

[0093] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0094] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A three-degree-of-freedom parallel mechanism with two rotations and one transfer in space, comprising: Determine the platform; Dynamic platform; Three identical main branches support the moving platform in achieving three degrees of freedom motion. The three degrees of freedom motion includes two rotational motions about two skew axes in space, and one translational motion along the normal direction of the fixed platform. Each main branch includes a first branch and a second branch. The first end of the first branch and the first end of the second branch are connected to the spherical surface of the moving platform via an equivalent ball joint. The second end of the first branch is rotatably connected to the fixed platform, and the second end of the second branch is rotatably connected to the fixed platform via a revolute joint. Each of the first branch chains includes; The first upper connecting rod has its first end connected to the moving platform via the equivalent ball joint. The first lower connecting rod has its first end rotatably connected to the second end of the first upper connecting rod via a first revolute joint, and the second end of the first lower connecting rod is rotatably connected to the fixed platform via a second revolute joint. Each second branch chain includes: The first end of the second upper link is connected to the first end of the first upper link and the moving platform respectively through the equivalent ball joint; The first end of the second lower connecting rod is rotatably connected to the second end of the second upper connecting rod via a third revolute joint, and the second end of the second lower connecting rod is rotatably connected to the fixed platform via a fourth revolute joint.

2. The mechanism according to claim 1, wherein, The equivalent ball joint includes: A first rotating shaft is rotatably connected to the moving platform, and the rotation axis of the first rotating shaft is perpendicular to the moving platform; The second rotating shaft is rotatably connected to the first rotating shaft, and the rotation axis of the second rotating shaft is perpendicular to the rotation axis of the first rotating shaft; A third rotating shaft is rotatably connected to the second rotating shaft, and the rotation axis of the third rotating shaft is perpendicular to the rotation axis of the second rotating shaft and the axis of the first rotating shaft, respectively.

3. The mechanism according to claim 1, wherein, The arrangement of the second and fourth revolute joints of each of the main branches includes: The arrangement points of each of the second revolute joints are evenly distributed on the arc of the first circumcircle, and the axis of each of the second revolute joints is tangent to the first circumcircle; wherein, the first circumcircle is the circumcircle formed by the connection points of each of the second revolute joints and the fixed platform; The arrangement points of each of the fourth revolute joints are evenly distributed on the arc of the second circumcircle, and the axis of each of the fourth revolute joints is tangent to the second circumcircle; wherein, the second circumcircle is the circumcircle formed by the connection points of each of the fourth revolute joints and the fixed platform; The diameter of the first circumcircle is larger than the diameter of the second circumcircle.

4. The mechanism according to claim 1, wherein, The axes of the first revolute joint, the second revolute joint, the third revolute joint, and the fourth revolute joint in each of the main branches are parallel to each other.

5. The mechanism according to claim 1, wherein, The arrangement points of each of the equivalent ball joints are evenly distributed on the arc of the third circumcircle of the moving platform; wherein, the third circumcircle is the circumcircle formed by the connection points of each of the equivalent ball joints and the moving platform.

6. The mechanism according to claim 1, wherein, Also includes: Six power sources are provided, each of which is connected to each of the second and fourth rotating joints. The power sources are used to drive the second and fourth rotating joints in each of the main branches, so that the first lower connecting rod and the second lower connecting rod rotate relative to the fixed platform. The two rotational motions about the two axes of the skew space, and the one translational motion along the normal of the fixed platform, include: While the first lower connecting rod and the second lower connecting rod rotate relative to the fixed platform, they respectively drive the first upper connecting rod and the second upper connecting rod to rotate relative to the first lower connecting rod and the second lower connecting rod. While the first upper link and the second upper link rotate relative to the first lower link and the second lower link, they drive the moving platform to perform spherical motion relative to the first upper link and the second upper link. While the moving platform performs spherical motion relative to the first upper link and the second upper link, it also achieves two rotational motions around two axes of skew surfaces in space, and one translational motion along the normal of the fixed platform.

7. A mechanical device, wherein, Includes the three-degree-of-freedom parallel mechanism as described in any one of claims 1 to 6.

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