A double platform hexapod robot based on motion bifurcation parallel mechanism

Abstract

The application belongs to the field of mobile robots, and particularly relates to a double-platform six-legged robot based on motion bifurcation parallel mechanism, which comprises an upper platform (a platform for carrying objects), a lower platform, four motion branch chains and six telescopic legs. The upper platform and the lower platform are connected through the four motion branch chains, the first branch chain and the second branch chain are RPU branch chains, the third branch chain and the fourth branch chain are UPR branch chains, and the robot moves through the alternate motion of the upper and lower platforms. The upper platform and the lower platform are respectively provided with three telescopic legs, which can be elongated by a corresponding distance according to the terrain. In the initial configuration, the robot has 2T2R instantaneous degrees of freedom. The application has two different motion modes of 2T1R and 1T1R, when the robot moves forward or backward, the robot is in the 2T1R motion mode, and when the robot turns, the robot is in the 1T1R motion mode. In the two motion modes, the robot is redundantly driven, the coupling degrees are both zero, and the robot has an analytical position direct solution, so that the movement demand of the robot can be met.

Description

Technical Field

[0001] This invention belongs to the field of mobile robots, specifically relating to a dual-platform hexapod robot based on a motion bifurcation parallel mechanism. Background Technology

[0002] With the continuous advancement of urbanization, the development and utilization of urban underground spaces in my country, such as abandoned coal mines, has entered a stage of rapid growth. Underground spaces pose high environmental safety risks, and the coverage of traditional manual inspection methods is limited. Mobile robots can replace humans in performing high-risk tasks in dangerous and complex underground spaces, reducing the risk costs of underground space redevelopment projects and playing a significant role in the development and utilization of underground spaces.

[0003] Parallel mechanisms have advantages such as high rigidity and high load-bearing capacity. Most existing parallel mobile robots use parallel mechanisms as the legs of multi-legged robots. However, the control system is complex. Platform-type parallel mobile robots achieve robot movement through the alternating motion between multiple platforms. Compared with parallel legged mobile robots, the structure is more compact and has stronger rigidity and load-bearing capacity. However, most of the existing platform-type parallel mobile robots use traditional parallel mechanisms with a single motion mode and no analytical forward position solution, which brings inconvenience to their subsequent performance analysis and real-time motion control. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism, comprising an upper platform (carrying platform), a lower platform, four kinematic branches, and six telescopic legs.

[0005] The upper platform and the lower platform are connected by four motion branches to form a motion bifurcation parallel mechanism. Each motion branch includes a driving component. The first and second branches are RPU branches, and the third and fourth branches are UPR branches. The six telescopic feet can be divided into two groups, each group having three upper platform telescopic feet and three lower platform telescopic feet. The three upper platform telescopic feet are connected to the upper platform, and the three lower platform telescopic feet are connected to the lower platform.

[0006] Furthermore, the connection points of the first branch, the second branch, the third branch, and the fourth branch at the upper and lower platforms respectively form two identical isosceles triangles.

[0007] Furthermore, the connection points of the three upper platform telescopic feet with the upper platform form an isosceles triangle, and the connection points of the three lower platform telescopic feet with the lower platform form an isosceles triangle. The height of the isosceles triangle formed by the three upper platform telescopic feet is greater than the height of the isosceles triangle formed by the three lower platform telescopic feet. Furthermore, the first branch and the second branch are both RPU branches. The first branch and the second branch are respectively connected to the upper platform through a first revolute joint and a second revolute joint. The first branch and the second branch are respectively connected to the lower platform through a first Hooke joint and a second Hooke joint. The first revolute joint is connected to the first Hooke joint through a first prismatic joint, and the second revolute joint is connected to the second Hooke joint through a second prismatic joint.

[0008] Furthermore, the third and fourth branches are both UPR branches. The third and fourth branches are connected to the upper platform through the third and fourth Hooke joints, respectively. The third and fourth branches are connected to the lower platform through the third and fourth revolute joints, respectively. The third Hooke joint is connected to the third revolute joint through the third prismatic joint, and the fourth Hooke joint is connected to the fourth revolute joint through the second prismatic joint.

[0009] Furthermore, the rotation axes of the first and second revolute joints are parallel to each other, and the two rotation axes of the first and second Hooke joints coincide. One rotation axis is parallel to the rotation axis of the first revolute joint, and the other rotation axis is perpendicular to the lower platform.

[0010] Furthermore, the rotation axes of the third and fourth rotary joints are parallel to each other, and the two rotation axes of the third and fourth Hooke joints coincide. One rotation axis is parallel to the rotation axis of the third rotary joint, and the other rotation axis is perpendicular to the upper platform.

[0011] Furthermore, the rotation of the first sliding joint of the first branch, the second sliding joint of the second branch, the third sliding joint of the third branch, the fourth sliding joint of the fourth branch, the third Hooke joint, and the fourth Hooke joint perpendicular to the upper platform is considered as an active kinematic pair.

[0012] Furthermore, the upper platform telescopic foot is composed of an upper platform connecting rod, an upper platform lower connecting rod, a drive intermediate support plate, a drive extension rod, a driven upper connecting rod, a driven lower connecting rod, and an upper platform shock-absorbing foot end. The drive extension rod is connected to the upper platform lower connecting rod, and the upper platform lower connecting rod is connected to the upper platform shock-absorbing foot end. One end of the driven upper connecting rod is connected to the upper platform, and the other end is connected to the drive intermediate support plate. One end of the driven lower connecting rod is connected to the upper platform shock-absorbing foot end. The upper platform connecting rod and the upper platform lower connecting rod form an active sliding pair, which drives the upper platform foot end to extend a corresponding distance according to the terrain. The driven upper connecting rod and the driven lower connecting rod form a driven sliding pair, which moves the same distance as the active sliding pair.

[0013] Furthermore, the telescopic foot is composed of a lower platform connector, a lower platform connecting rod, a lower platform lower connecting rod, and a lower platform shock-absorbing foot end. The lower platform connecting rod is connected to the lower platform through the lower platform connector, and the lower platform shock-absorbing foot end is connected to the lower platform lower connecting rod. The lower platform connecting rod and the lower platform lower connecting rod constitute an active sliding pair.

[0014] Compared with the prior art, the present invention achieves the following technical effects: In the initial configuration, the upper platform and the lower platform are parallel and the coordinate system of the lower platform is... z Axial Platform Coordinate System Z In the axial direction, the robot has two rotational degrees of freedom and two translational degrees of freedom. When the third and fourth Hooke hinges are locked perpendicular to the upper platform, the active kinematic pairs driving the four kinematic chains cause the robot to rotate along... X Axis movement or rotation X When the axis rotates, the robot only has a 2T1R motion mode. When the rotation of the third and fourth Hooke hinges perpendicular to the upper platform is released, the active kinematic pairs of the four kinematic chains drive the robot to rotate... Z When the axis rotates, the robot only has a 1T1R motion mode. To achieve complete control over the upper and lower platforms, the robot uses five active kinematic pairs to control the motion of the upper and lower platforms during the initial configuration. In the 2T1R and 1T1R motion modes, the robot uses four active kinematic pairs for redundant drive. In both motion modes, the robot has an analytical forward position solution, overcoming the limitations of platform-type parallel mobile robots which have a single motion mode and lack analytical forward position solutions. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments according to the invention and, together with the description, serve to explain the principles of the invention.

[0016] Figure 1 This is a schematic diagram of the overall structure of the dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism as described in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the kinematic branch structure in the dual-platform hexapod robot based on the kinematic bifurcation parallel mechanism described in an embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the upper platform telescopic leg of the dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism as described in an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the lower platform telescopic leg of the dual-platform hexapod robot based on a motion bifurcation parallel mechanism as described in an embodiment of the present invention.

[0020] Figure 5This is a schematic diagram of the forward movement of a dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism, as described in an embodiment of the present invention.

[0021] Figure 6 This is a schematic diagram of a dual-platform hexapod robot turning based on a kinematic bifurcation parallel mechanism, as described in an embodiment of the present invention.

[0022] Explanation of reference numerals in the attached figures: 1-Upper platform (carrying platform); 2-Lower platform; 3-Kinematic chain; 3.1-First chain; 3.1.1-First revolute joint; 3.1.2-First prismatic joint; 3.1.3-First Hooke joint; 3.2-Second chain; 3.2.1-Second revolute joint; 3.2.2-Second prismatic joint; 3.2.3-Second Hooke joint; 3.3-Third chain; 3.3.1-Third Hooke joint; 3.3.2-Third prismatic joint; 3.3.3-Third revolute joint; 3.4-Fourth chain; 3.4.1-Fourth Hooke joint; 3.4.2-... 4.4.3 - Fourth rotating joint; 4 - Telescopic foot; 4.1 - Upper platform telescopic foot; 4.1.1 - Upper platform connecting rod; 4.1.2 - Upper platform lower connecting rod; 4.1.3 - Drive intermediate support plate; 4.1.4 - Drive extension rod; 4.1.5 - Driven upper connecting rod; 4.1.6 - Driven lower connecting rod; 4.1.7 - Upper platform shock-absorbing foot end; 4.2 - Lower platform telescopic foot; 4.2.1 - Lower platform connector; 4.2.2 - Lower platform upper connecting rod; 4.2.3 - Lower platform lower connecting rod; 4.2.4 - Lower platform shock-absorbing foot end. Detailed Implementation

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Reference Figures 1 to 6 As shown, this example provides a dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism, including an upper platform (carrying platform) 1, a lower platform 2, four kinematic branches 3, and six telescopic legs 4.

[0025] Among them, reference Figure 1 and Figure 2 As shown, the upper platform 1 and the lower platform 2 are connected by four motion branches 3 to form a motion bifurcation parallel mechanism. Each motion branch 3 includes an active motion pair. The first branch 3.1 and the second branch 3.2 are both RPU branches, and the third branch 3.3 and the fourth branch 3.4 are both UPR branches.

[0026] Specifically, the first branch 3.1, the second branch 3.2, the third branch 3.3, and the fourth branch 3.4 form two identical isosceles triangles at the connection points of the upper platform 1 and the lower platform 2, respectively.

[0027] Specifically, the connection points of the three upper platform telescopic feet 4.1 with the upper platform 1 form an isosceles triangle, and the connection points of the three lower platform telescopic feet 4.2 with the lower platform 2 form an isosceles triangle. The height of the isosceles triangle formed by the three upper platform telescopic feet 4.1 is greater than the height of the isosceles triangle formed by the three lower platform telescopic feet 4.2.

[0028] Specifically, both the first branch 3.1 and the second branch 3.2 are RPU branches. The first branch 3.1 and the second branch 3.2 are connected to the upper platform 1 via the first revolute joint 3.1.1 and the second revolute joint 3.2.1, respectively. The first branch 3.1 and the second branch 3.2 are connected to the lower platform 2 via the first Hooke joint 3.1.3 and the second Hooke joint 3.2.3, respectively. The first revolute joint 3.1.1 is connected to the first Hooke joint 3.1.3 via the first prismatic joint 3.1.2, and the second revolute joint 3.2.1 is connected to the second Hooke joint 3.2.3 via the second prismatic joint 3.2.2. Next, the third branch 3.3 and the fourth branch 3.4 are both UPR branches. The third branch 3.3 and the fourth branch 3.4 are connected to the upper platform 1 through the third Hooke hinge 3.3.1 and the fourth Hooke hinge 3.4.1, respectively. The third branch 3.3 and the fourth branch 3.4 are connected to the lower platform 2 through the third revolute joint 3.3.3 and the fourth revolute joint 3.4.3, respectively. The third Hooke hinge 3.3.1 is connected to the third revolute joint 3.3.3 through the third prismatic joint 3.3.2. The fourth Hooke hinge 3.4.1 is connected to the fourth revolute joint 3.4.3 through the second prismatic joint 3.4.2.

[0029] Specifically, the rotation axes of the first revolute joint 3.1.1 and the second revolute joint 3.2.1 are parallel to each other, and the two rotation axes of the first Hooke joint 3.1.3 and the second Hooke joint 3.2.3 coincide. One rotation axis is parallel to the rotation axis of the first revolute joint 3.1.1, and the other rotation axis is perpendicular to the lower platform 2.

[0030] Specifically, the rotation axes of the third revolute joint 3.3.3 and the fourth revolute joint 3.4.3 are parallel to each other, and the two rotation axes of the third Hooke joint 3.3.1 and the fourth Hooke joint 3.4.1 coincide. One rotation axis is parallel to the rotation axis of the third revolute joint 3.3.1, and the other rotation axis is perpendicular to the upper platform 1. In both motion modes, the robot possesses analytical forward position solutions, which is beneficial for robot performance analysis and real-time motion control.

[0031] Furthermore, referring to Figure 1 and Figure 3As shown, the six telescopic feet 4 can be divided into two groups, each group having three upper platform telescopic feet 4.1 and three lower platform telescopic feet 4.2. The three upper platform telescopic feet 4.1 are connected to the upper platform 1, and the three lower platform telescopic feet 4.2 are connected to the lower platform 2. To improve the load-bearing capacity of the upper platform 1, the upper platform telescopic feet 4.1 consist of an upper platform connecting rod 4.1.1, an upper platform lower connecting rod 4.1.2, a drive intermediate support plate 4.1.3, a drive extension rod 4.1.4, a driven upper connecting rod 4.1.5, a driven lower connecting rod 4.1.6, and an upper platform shock-absorbing foot end 4.1.7. The drive extension rod 4.1.4 is connected to the upper platform lower connecting rod 4.1.2, and the upper platform lower connecting rod 4.1.2 is connected to the upper platform shock-absorbing foot end 4.1.7. Link 4.1.5 is connected at one end to the upper platform 1 and at the other end to the drive intermediate support plate 4.1.3. One end of the driven lower link 4.1.6 is connected to the upper platform shock-absorbing foot 4.1.7. The upper platform link 4.1.1 and the upper platform lower link 4.1.2 form an active prismatic joint, causing the upper platform shock-absorbing foot 4.1.7 to extend a corresponding distance according to the terrain. The driven upper link 4.1.5 and the driven lower link 4.1.6 form a driven prismatic joint, moving the same distance as the active prismatic joint. The upper platform telescopic foot 4.1, by setting up active and driven prismatic joints, increases the force-bearing area of ​​the foot end, improving the robot's load-bearing capacity. The upper platform shock-absorbing foot 4.1.7 can reduce the impact between the ground and the upper platform telescopic foot 4.1.

[0032] Furthermore, referring to Figure 1 and Figure 4 As shown, the lower platform telescopic foot 4.2 consists of a lower platform connector 4.2.1, a lower platform connecting rod 4.2.2, a lower platform lower connecting rod 4.2.3, and a lower platform shock-absorbing foot end 4.2.4. The lower platform connecting rod 4.2.2 is connected to the lower platform 2 through the lower platform connector 4.2.1, and the lower platform shock-absorbing foot end 4.2.4 is connected to the lower platform lower connecting rod 4.2.3. The lower platform connecting rod 4.2.2 and the lower platform lower connecting rod 4.2.3 form an active sliding pair, which drives the lower platform shock-absorbing foot end 4.2.4 to extend a corresponding distance according to the terrain. The lower platform shock-absorbing foot end 4.2.4 can reduce the impact between the ground and the lower platform telescopic foot 4.2.

[0033] Furthermore, referring to Figure 5 and Figure 6As shown, in the initial configuration, the rotation of the first prismatic joint 3.1.2, the second prismatic joint 3.2.2, the third prismatic joint 3.3.2, the fourth prismatic joint 3.4.2, the third Hooke hinge (3.3.1), and the fourth Hooke hinge (3.4.1) perpendicular to the upper platform (1) serves as the active kinematic joint. In both motion modes, the first prismatic joint 3.1.2, the second prismatic joint 3.2.2, the third prismatic joint 3.3.2, and the fourth prismatic joint 3.4.2 serve as active joints, and the robot is redundantly driven, achieving optimized distribution of the robot's driving force and reducing the requirements for the stiffness of the kinematic branches and the load capacity of the active kinematic joints.

[0034] Specifically, the robot moves by alternating motions of the upper platform 1 and the lower platform 2. When the robot moves forward, the rotation perpendicular to the upper platform is locked in the third Hooke hinge 3.3.1 and the fourth Hooke hinge 3.4.1, at which point the robot has a 2T1R motion mode. First, the upper platform's extendable foot 4.1 contacts the ground, and the upper platform 1 remains stationary. The lower platform 2 moves forward, rises, and adjusts its posture by driving the first prismatic joint 3.1.2, the second prismatic joint 3.2.2, the third prismatic joint 3.3.2, and the fourth prismatic joint 3.4.2. Then, the lower platform's extendable foot 4.2 contacts the ground, and the lower platform 2 remains stationary. The upper platform 1 moves forward, rises, and adjusts its posture by driving the first prismatic joint 3.1.2, the second prismatic joint 3.2.2, the third prismatic joint 3.3.2, and the fourth prismatic joint 3.4.2, allowing the upper platform 1 and the lower platform 2 to move alternately. When the robot turns, the rotation perpendicular to the upper platform in the third Hooke hinge 3.3.1 and the fourth Hooke hinge 3.4.1 is released. At this time, the robot has a 1T1R motion mode, and the robot turns by alternating rotation of the upper platform 1 and the lower platform 2. This mobile robot has two different motion modes, which can be switched according to the robot's movement requirements.

[0035] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism, characterized in that: It includes an upper platform (carrying platform) (1), a lower platform (2), four motion chains (3), and six telescopic legs (4); The upper platform (1) and the lower platform (2) are connected by four motion branches (3) to form a motion bifurcation parallel mechanism. Each motion branch (3) includes a driving component. The first branch (3.1) and the second branch (3.2) are both RPU branches, and the third branch (3.3) and the fourth branch (3.4) are both UPR branches. The six telescopic feet (4) can be divided into two groups. Each group has three upper platform telescopic feet (4.1) and three lower platform telescopic feet (4.2). The three upper platform telescopic feet (4.1) are connected to the upper platform (1), and the three lower platform telescopic feet (4.2) are connected to the lower platform (2).

2. The dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism according to claim 1, characterized in that: The first branch (3.1), the second branch (3.2), the third branch (3.3), and the fourth branch (3.4) form two identical isosceles triangles at the connection points of the upper platform (1) and the lower platform (2); The connection points of the three upper platform telescopic feet (4.1) and the upper platform (1) form an isosceles triangle, and the connection points of the three lower platform telescopic feet (4.2) and the lower platform (2) form an isosceles triangle. The height of the isosceles triangle formed by the three upper platform telescopic feet (4.1) is greater than the height of the isosceles triangle formed by the three lower platform telescopic feet (4.2).

3. A dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism according to claim 1, characterized in that: The first branch (3.1) and the second branch (3.2) are both RPU branches. The first branch (3.1) and the second branch (3.2) are connected to the upper platform (1) through the first revolute joint (3.1.1) and the second revolute joint (3.2.1) respectively. The first branch (3.1) and the second branch (3.2) are connected to the lower platform (2) through the first Hooke joint (3.1.3) and the second Hooke joint (3.2.3) respectively. The first revolute joint (3.1.1) is connected to the first Hooke joint (3.1.3) through the first prismatic joint (3.1.2). The second revolute joint (3.2.1) is connected to the second Hooke joint (3.2.3) through the second prismatic joint (3.2.2). The third branch (3.3) and the fourth branch (3.4) are both UPR branches. The third branch (3.3) and the fourth branch (3.4) are connected to the upper platform (1) through the third Hooke hinge (3.3.1) and the fourth Hooke hinge (3.4.1) respectively. The third branch (3.3) and the fourth branch (3.4) are connected to the lower platform (2) through the third revolute joint (3.3.3) and the fourth revolute joint (3.4.3) respectively. The third Hooke hinge (3.3.1) is connected to the third revolute joint (3.3.3) through the third prismatic joint (3.3.2). The fourth Hooke hinge (3.4.1) is connected to the fourth revolute joint (3.4.3) through the second prismatic joint (3.4.2).

4. A dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism according to claim 3, characterized in that: The rotation axes of the first revolute joint (3.1.1) and the second revolute joint (3.2.1) are parallel to each other, the two rotation axes of the first Hooke joint (3.1.3) and the second Hooke joint (3.2.3) coincide, and one rotation axis is parallel to the first revolute joint (3.1.1). The rotation axes of 3.1.1) are parallel to each other, and the other rotation axis is perpendicular to the lower platform (2); The rotation axes of the third rotary joint (3.3.3) and the fourth rotary joint (3.4.3) are parallel to each other. The two rotation axes of the third Hooke joint (3.3.1) and the fourth Hooke joint (3.4.1) coincide. One rotation axis is parallel to the rotation axis of the third rotary joint (3.3.1), and the other rotation axis is perpendicular to the upper platform (1).

5. A dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism according to claim 1, characterized in that: The first sliding joint (3.1.2) of the first branch (3.1), the second sliding joint (3.2.2) of the second branch (3.2), the third sliding joint (3.3.2) of the third branch (3.3), the fourth sliding joint (3.4.2) of the fourth branch (3.4), the third Hooke joint (3.3.1) and the fourth Hooke joint (3.4.1) rotate perpendicularly to the upper platform (1) as active kinematic pairs.

6. A dual-platform hexapod robot based on a kinematic bifurcation parallel mechanism according to claim 1, characterized in that: The upper platform telescopic foot (4.1) consists of an upper platform connecting rod (4.1.1), an upper platform lower connecting rod (4.1.2), and a drive intermediate support plate (4.1.2). The structure consists of a drive extension rod (4.1.3), a driven upper connecting rod (4.1.5), a driven lower connecting rod (4.1.6), and an upper platform damping foot (4.1.7). The drive extension rod (4.1.4) is connected to the upper platform lower connecting rod (4.1.2), and the upper platform lower connecting rod (4.1.2) is connected to the upper platform damping foot (4.1.7). One end of the driven upper connecting rod (4.1.5) is connected to the upper platform (1), and the other end is connected to the drive intermediate... The support plate (4.1.3) is connected, and one end of the driven lower link (4.1.6) is connected to the shock-absorbing foot end (4.1.7) of the upper platform. The upper platform link (4.1.1) and the upper platform lower link (4.1.2) form an active sliding pair, which drives the upper platform shock-absorbing foot end (4.1.7) to extend a corresponding distance according to the terrain. The driven upper link (4.1.5) and the driven lower link (4.1.6) form a driven sliding pair, which moves the same distance as the active sliding pair. The lower platform telescopic foot (4.2) is composed of a lower platform connector (4.2.1), a lower platform connecting rod (4.2.2), a lower platform lower connecting rod (4.2.3), and a lower platform shock-absorbing foot end (4.2.4). The lower platform connecting rod (4.2.2) is connected to the lower platform (2) through the lower platform connector (4.2.1), and the lower platform shock-absorbing foot end (4.2.4) is connected to the lower platform lower connecting rod (4.2.3). The lower platform connecting rod (4.2.2) and the lower platform lower connecting rod (4.2.3) constitute an active sliding pair.

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