Variable-stiffness plane parallel positioning platform with flexible hinges capable of switching contact states

Abstract

The invention discloses a variable-stiffness plane parallel positioning platform with flexible hinges capable of switching contact states, and belongs to the field of parallel robots. The positioning platform comprises a movable platform, four static platforms are arranged in the circumferential direction of the movable platform, and branched chains are arranged between the static platforms and the movable platform; each branch chain comprises two sets of flexible hinges, and the two sets of flexible hinges are correspondingly fixed to the static platform and the movable platform. The number of the flexible hinges in each group is two, the flexible hinges are distributed up and down, and the two flexible hinges in each group are fixed through a connecting piece; the two connecting pieces are connected through a linear actuator, and the distance between the static platform and the movable platform can be adjusted. The flexible hinge deforms in the circumferential direction when being stressed, and relative torsion of the static platform and the movable platform can be achieved. And the joint rigidity is adjusted by changing the parameters such as the pre-tightening force and the gap of the hinge, so that the stability and the movement precision of the mechanism are improved, the dynamic response of the mechanism is optimized, and the response speed and the stability of the mechanism under the rapid change load are improved.

Description

Technical Field

[0001] The present invention belongs to the field of parallel robots, and particularly relates to a variable-stiffness planar parallel positioning platform with flexible hinges having switchable contact states. Background Art

[0002] With the development of modern technology, especially in the fields of microelectronics manufacturing, aerospace equipment, micromanipulators, ultra-precision machining, semiconductor assembly, and optical communication, higher and higher requirements are put forward for the accuracy, stability, and reliability of mechanical drive and transmission systems. Traditional mechanical drive and transmission systems face many challenges in these fields, such as insufficient accuracy, poor stability, limited load-bearing capacity, and slow dynamic response. Therefore, it is of great significance to develop a mechanical drive and transmission system with high precision, high stability, large working space, and high load-bearing capacity.

[0003] Among them, a patent application with the publication number CN115592653A proposes an application to a planar three-degree-of-freedom redundant parallel mechanism, using traditional hinge blocks as the traditional hinge structure between the moving platform and the telescopic rod and the rotating rod to achieve rotational degrees of freedom. However, due to the T-shaped rod structure, more space may be required to accommodate its structure, which is a limitation in applications with limited space.

[0004] The patent application with the publication number CN105936045A proposes a partially decoupled six-degree-of-freedom parallel mechanism. Although it uses a composite spherical hinge to replace the traditional T-shaped rod structure, reducing the complexity and space requirements of the mechanism, the mechanism still exhibits singular phenomena when the telescopic rods are symmetrically distributed and coplanar with the normal of the moving platform. This limits the movement range of the mechanism. At the same time, when the rotation angle increases, the support stiffness will decrease significantly. When the mechanism approaches the motion limit, due to the accumulation of internal stress, the stiffness change will be more obvious.

[0005] Therefore, a variable-stiffness planar parallel positioning platform with flexible hinges having switchable contact states is proposed. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a variable-stiffness planar parallel positioning platform with flexible hinges having switchable contact states, which solves the problems in the prior art.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] Variable-stiffness planar parallel positioning platform with flexible hinges having switchable contact states, including a moving platform, four static platforms are circumferentially arranged on the moving platform, and a branch chain is arranged between the static platform and the moving platform; the branch chain includes two groups of flexible hinges, and the two groups of flexible hinges are relatively fixed to the static platform and the moving platform respectively; the number of flexible hinges in each group is two, and they are distributed vertically, and the two flexible hinges in each group are fixed by a connecting piece; the distance between the two connecting pieces is connected by a linear actuator and can be adjusted between the static platform and the moving platform;

[0009] When the flexible hinge is subjected to external force and torque, it deforms and can realize the relative torsion between the static platform and the moving platform.

[0010] Further, the flexible hinge includes two fan-shaped connection regions and two fan-shaped hollow regions that are symmetrically distributed in the circumferential direction, and the fan-shaped connection regions and the fan-shaped hollow regions are spaced apart; a fixed end is provided at each end of the fan-shaped hollow region, and the fixed end is relatively fixed to the corresponding static platform and the moving platform; the fan-shaped connection region is fixed to the connecting piece.

[0011] Further, a section one and a section four are respectively provided at the two edges of the fan-shaped hollow region; a section three in a T shape is provided at the hollow part in the middle of the fan-shaped hollow region, and a section two is provided at the edge of the hollow part in the middle.

[0012] Further, when the flexible hinge is subjected to the tangential force transmitted by the connecting piece, the fan-shaped connection region deforms towards the fan-shaped hollow region, and at the same time, the section one and the section four also deform, and the section three rotates at the hollow part in the middle; as the flexible hinge continues to deform, the section three can contact the section two and generate friction to increase the stiffness of the flexible hinge.

[0013] Further, the linear actuator is fixed on one of the connecting pieces, and the push rod of the linear actuator is fixed to the other connecting piece.

[0014] Further, the linear actuator is fixed to one of the connecting pieces by bolts, and the push rod of the linear actuator is fixed to the other connecting piece by bolts and nuts.

[0015] Further, a cover plate is fixed to the upper end of the static platform by a bolt connection method, and the cover plate is fixed to the flexible hinge by a bolt connection method.

[0016] Further, cover plates are respectively fixed to the eight corners at the upper and lower ends of the moving platform by bolts, and the flexible hinge is fixed to the cover plate by a bolt connection method.

[0017] Further, the material of the flexible hinge is spring steel.

[0018] A parallel robot, comprising the variable stiffness planar parallel positioning platform with flexible hinges having switchable contact states as described above.

[0019] Advantages of the present invention:

[0020] 1. The redundant drive in the present invention provides an additional degree of freedom, thereby reducing or avoiding singular configurations, effectively expanding the working space of the mechanism and significantly enhancing the system stability.

[0021] 2. The flexible hinge structure with switchable contact states adopted in the present invention has a simple design. Compared with traditional T-shaped rod structures and multi-degree-of-freedom parallel mechanisms, the number of components and connection nodes is greatly reduced, not only reducing the complexity of the mechanical structure, but also simplifying the algorithm design of the control system.

[0022] 3. The flexible hinge with switchable contact states in the present invention realizes the dynamic regulation of joint stiffness by adjusting key geometric parameters such as the pre-tightening force and clearance of the hinge, providing an efficient stiffness regulation scheme. This scheme can achieve precise control of joint stiffness, thereby significantly improving the motion accuracy and stability of the mechanism. In addition, this adjustable stiffness characteristic can also optimize the dynamic performance of the mechanism, enabling it to maintain excellent response speed and operating stability under rapidly changing load conditions. Description of the drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 is a three-dimensional view of the variable stiffness planar parallel positioning platform with flexible hinges having switchable contact states of the present invention;

[0025] Figure 2 is a right view of the variable stiffness planar parallel positioning platform with flexible hinges having switchable contact states of the present invention;

[0026] Figure 3 is a top view of the variable stiffness planar parallel positioning platform with flexible hinges having switchable contact states of the present invention;

[0027] Figure 4 is a three-dimensional view of a single chain of the present invention;

[0028] Figure 5 is a dimensional analysis diagram of the variable stiffness planar parallel positioning platform with flexible hinges having switchable contact states of the present invention;

[0029] Figure 6It is a three-dimensional configuration diagram of the flexible hinge of the present invention;

[0030] Figure 7 It is a dimensional design diagram of the flexible hinge of the present invention;

[0031] Figure 8 It is a coordinate positioning and force diagram of the flexible hinge of the present invention;

[0032] Figure 9 It is a deformation switching flow chart of the flexible hinge of the present invention;

[0033] Figure 10 It is a displacement variable stiffness flow chart of the variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to the present invention.

[0034] In the figure: 1 - First static platform, 2 - First branch chain, 3 - First cover plate, 4 - Second cover plate, 5 - Third cover plate, 6 - Second static platform, 7 - Second branch chain, 8 - Fourth cover plate, 9 - Fifth cover plate, 10 - Sixth cover plate, 11 - Third static platform, 12 - Third branch chain, 13 - Seventh cover plate, 14 - Eighth cover plate, 15 - Ninth cover plate, 16 - Moving platform, 17 - Fourth static platform, 18 - Fourth branch chain, 19 - Tenth cover plate, 20 - Eleventh cover plate, 21 - Twelfth cover plate, 22 - First flexible hinge, 23 - First connecting piece, 24 - Second flexible hinge, 25 - Linear actuator, 26 - Third flexible hinge, 27 - Second connecting piece, 28 - Fourth flexible hinge; 29 - Fixed end, 30 - Segment one, 31 - Segment two, 32 - Segment three, 33 - Segment four, 34 - Sector connecting area, 35 - Sector hollow area. Detailed implementation manners

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0036] Embodiment 1

[0037] As Figures 1 to 4As shown in the figure, a variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state includes a moving platform 16. The first static platform 1, the second static platform 6, the third static platform 11, and the fourth static platform 17 are arranged on the peripheral side of the moving platform 16 and are fixedly connected to each other to form a square frame. The first static platform 1, the second static platform 6, the third static platform 11, and the fourth static platform 17 are respectively connected to the moving platform 16 through the first link 2, the second link 7, the third link 12, and the fourth link 18, and the first link 2, the second link 7, the third link 12, and the fourth link 18 are equally spaced on the peripheral side of the moving platform 16.

[0038] Among them, the internal structures and installation methods of the first link 2, the second link 7, the third link 12, and the fourth link 18 are the same. Taking the first link 2 as an example, the structure and installation method of the link are introduced as follows:

[0039] As Figure 4 shown in the figure, the first link 2 includes: a first flexible hinge 22, a second flexible hinge 24, a third flexible hinge 26, and a fourth flexible hinge 28; the first flexible hinge 22 and the second flexible hinge 24 are arranged vertically and are both relatively fixed to the first static platform 1. The first flexible hinge 22 and the second flexible hinge 24 are fixedly connected through a first connecting member 23; the third flexible hinge 26 and the fourth flexible hinge 28 are arranged vertically and are both relatively fixed to the moving platform 16. The third flexible hinge 26 and the fourth flexible hinge 28 are fixedly connected through a second connecting member 27; a linear actuator 25 is fixedly installed on the first connecting member 23 by means of a bolt connection, and the push rod of the linear actuator 25 is fixedly connected to the second connecting member 27 through a bolt and nut;

[0040] When the flexible hinge is stressed, it deforms circumferentially, enabling relative torsion between the static platform and the moving platform 16; moreover, by controlling the linear actuator 25, the distance between the static platform and the moving platform 16 can be adjusted; the same applies to other links.

[0041] In this embodiment, a first cover plate 3, a fourth cover plate 8, a seventh cover plate 13, and a tenth cover plate 19 are respectively fixed to the upper ends of the first static platform 1, the second static platform 6, the third static platform 11, and the fourth static platform 17 by bolts; the flexible hinge is fixed to the cover plate by means of a bolt connection to achieve relative fixation between the flexible hinge and the static platform, facilitating the machining and manufacturing of the structure;

[0042] Similarly, at the four corners at the upper end of the moving platform 16, a third cover plate 5, a fifth cover plate 9, an eighth cover plate 14, and an eleventh cover plate 20 are respectively fixed by bolts; at the four corners at the lower end of the moving platform 16, a second cover plate 4, a sixth cover plate 10, a ninth cover plate 15, and a twelfth cover plate 21 are respectively fixed by bolts; the flexible hinge is fixed to the cover plate by means of bolt connection to realize the relative fixation between the flexible hinge and the moving platform 16, so as to facilitate the processing and manufacturing of the structure.

[0043] Embodiment 2

[0044] In this embodiment, a mechanical analysis is performed on the variable stiffness planar parallel positioning platform in Embodiment 1;

[0045] In this embodiment, the variable stiffness planar parallel positioning platform is driven by 4 linear actuators, and the degree of freedom of the end moving platform is 3, then the redundancy of its mechanism is re = 4 - 3 = 1. As Figure 5 shown, A i and C i respectively represent the torsion axis centers of the flexible hinges on the static platform and the torsion axis centers of the flexible hinges on the moving platform. O and O' respectively represent the global coordinate system and the local coordinate system of the end moving platform, and a i represents the position vector of A i relative to the global coordinate system O, and c i represents the position vector of C i relative to the global coordinate system O. r represents the Cartesian coordinate system of the end platform, and R represents the rotation matrix of the coordinate system O' relative to the coordinate system O;

[0046] Among them, the single-chain link length vector is

[0047] l i = a i - r - R×c i (1)

[0048] In the formula, l i is the chain vector, and its unit vector is:

[0049]

[0050] According to the Newton-Euler model, the static model of the end moving platform can be expressed as:

[0051] W×T = F (3)

[0052] In the formula, W ∈ R 3×4 is the Jacobian matrix, T ∈ R 4×1 is the thrust matrix, and F ∈ R 3×1 is the external force matrix (including the forces and torques acting on the end moving platform);

[0053]

[0054] When the structure matrix W is full rank, the thrust can be expressed as:

[0055] T=W + F+Nλ=t p +Nλ (5)

[0056] Where W + =W T (WW T ) -1 ∈R 4×3 is the Jacobian matrix; N is the null space matrix of the Jacobian matrix, expressed as N = null(W) = [N1, N2, N3, N4] T ∈R n×re ;t p =W + F represents the special solution of formula (3); λ∈R re×1 Represents an arbitrary column vector, and the thrust is adjusted through the null space vector λ to adapt to different external forces and moments.

[0057] The thrust feasible set of random column vector λ can be expressed as:

[0058] Ω={λ丨T min ≤Nλ+t p ≤T max} (6)

[0059] In formula (6), all columns (re) of N form a set of bases of the vector space, λ is the re-dimensional coordinate in the local coordinate system O, and through linear analysis, T min is the minimum tension of the branch link, T max is the maximum tension of the branch link. If the coordinate transformation matrix P is used -1 ∈R re×re , can be obtained by λ=V·P -1 Another coordinate V in the local coordinate system O is changed with λ to achieve the same thrust feasible set described by another set of coordinates in a similar vector space.

[0060] Since re = 1, any i-th linear actuator is selected for force control (1≤i≤4), and the following relationship exists:

[0061] N i λ+t pi =T i (7)

[0062]

[0063] Where λ = N C1 ×T i , t pi is the particular solution value of the thrust force of the linear actuator i. Substituting Equation (8) into Equation (5) gives the expression for the thrust force:

[0064]

[0065] where, N o = N·N C1 .

[0066] The set of feasible thrust forces that satisfy the condition that all links are within the linear force boundary is:

[0067]

[0068] Assume that the end effector is not in a geometrically singular pose. Select the i-th linear actuator for force control (1 ≤ i ≤ 4). Then the thrust force of the k-th (1 ≤ k ≤ 4, k ≠ i) linear actuator can be represented by T i as follows:

[0069] T k = t pk + N k1 ·N C1 (T i - t pi ) (11)

[0070] Using the Euler-Lagrange equation as the kinematic model, the following is the stiffness balance formula:

[0071] W T (q)·τ = Q(q) (12)

[0072] where W T (q) is the transpose of the Jacobian matrix, representing the conversion of joint torques to torques of the end effector. q are three independent coordinates, usually the Cartesian coordinates x ee , y ee of the end effector and its rotation θ ee . τ is the torque vector of the linear actuator, and Q(q) is the non-linear stiffness contribution of the flexible hinge. An effective solution for τ can be obtained from this equation, and all other solutions can be found by adding any vector in the null space of the Jacobian matrix W.

[0073] Example 3

[0074] In this example, the flexible hinge is described;

[0075] Based on the sectional flexible hinge and contact interaction, in this example, a design of internal force redundancy adjustable stiffness is added to the flexible hinge; according to the function of each flexible segment, it is divided into a contact segment and a non-contact segment;

[0076] As shown Figure 6 in the figure, the flexible hinge includes two sector connection regions 34 and two sector hollow regions 35 that are symmetrically distributed in the circumferential direction. The sector connection regions 34 and the sector hollow regions 35 are spaced apart and there is a gap between them. At both ends of the sector hollow region 35, a fixed end 29 is provided respectively, and the fixed end 29 is relatively fixed to the corresponding static platform and the moving platform 16 (i.e., fixed relatively by bolts with the corresponding cover plate to achieve relative fixation). The sector connection region 34 is used to fix the connecting members (the first connecting member 23 and the second connecting member 27).

[0077] On both edges of the sector hollow region 35, a first segment 30 and a fourth segment 33 are provided respectively as non-contact segments. In the middle hollow part of the sector hollow region 35, a T-shaped third segment 32 is provided, and at the edge of the middle hollow part, a second segment 31 is provided. The third segment 32 and the second segment 31 are used as contact segments.

[0078] The two-dimensional and three-dimensional diagrams of the flexible hinge when not deformed by force are respectively as shown Figure 8 in (a) of Figure 9 ; as shown Figure 9 in (b) of Z , when the flexible hinge is subjected to the tangential force F Figure 8 transmitted by the connecting member, the sector connection region 34 deforms towards the sector hollow region 35, and at the same time, the first segment 30 and the fourth segment 33 also deform, and the third segment 32 rotates at the middle hollow part; as shown Figure 9 in (b) of

[0079] and (c) of

[0080] , as the flexible hinge continues to deform, the third segment 32 will contact the second segment 31, thereby increasing the stiffness of the entire flexible hinge to achieve the purpose of changing the stiffness of the positioning platform. Figure 7 Specifically: The overall model of the branch chain with the flexible hinge is represented by a set of parameters, see

[0081] Table 1: Dimension analysis table of the flexible hinge

[0082]

[0083] Among them, the flexible hinge fixed to the fixed platform is the inner ring s flexible hinge, and the flexible hinge fixed to the moving platform is the inner ring e flexible hinge. At the hinge level, the flexible hinge is characterized by its diameter A se , the diameter D of the hollowed-out area se , height h and thickness t. The first two are the diameters A se and the diameter D of the hollowed-out area se obtained based on the finite element analysis of the spring steel set for the flexible hinge, and the latter two dimensions are fixed for all flexible hinges. The minimum thickness t can reduce the accumulation of stress without having too much impact on the supporting rigidity, and the height h is Figure 7 the out-of-plane dimension of the flexible hinge in Figure 7 , which is set to a fixed value. To achieve the optimal performance of the outer ring s and inner ring e flexible hinges (specifically, s is the flexible hinge fixed to the fixed platform, and e is the flexible hinge fixed to the moving platform), it is necessary to optimize Figure 7 the clearance angles ε s and ε e shown. Therefore, these angles are fixed as the minimum estimated clearance angles required for the expected motion range.

[0084] The coordinate system of a single flexible hinge is defined as shown in (a) of Figure 9 , and at this time, the stiffness matrix of a single flexible hinge can be expressed as

[0085]

[0086] where E is the elastic modulus of the flexible hinge, A se is the diameter of the flexible hinge, h is the height of the flexible hinge, k 11 represents the stiffness of the flexible hinge in the z-axis direction, k 22 represents the stiffness of the flexible hinge in the x-axis direction, k 33 represents the stiffness of the flexible hinge in the y-axis direction, k 44 represents the torsional stiffness of the flexible hinge around the x-axis, k 55 represents the torsional stiffness of the flexible hinge in the y-axis direction, k 66 represents the torsional stiffness of the flexible hinge around the z-axis direction.

[0087] Then, a torque M Z around the z-axis and a thrust (tangential force) F Z with a distance of S = 4 mm from the z-axis are applied to the flexible hinge as shown in (b) of Figure 9 . Its deformation is as shown in Figure 9 . According to the contact situation of the flexible segment, the motion of the hinge is divided into three stages: (a) The flexible hinge is not stressed, L is a fixed non-zero positive value, θ = 0°, and the stiffnesses k 11 , k 22 , k 33 , k44 and k 55 and k 66 remain unchanged; (b) The flexible hinge deforms. At this time, the deformation of segment 1 (30) and segment 4 (33) contributes to the movement, but the segments do not come into contact. 0 < L1 < L, 0 < θ1 < θ2, and the stiffnesses k 11 and k 22 and k 33 and k 44 and k 55 and k 66 still remain unchanged; (c) As the deformation increases, segment 3 (32) will contact and friction-lock with segment 2 (31), L2 = 0, and θ2 is a fixed non-zero positive value. At this stage, the effective length shortens, and the stiffness of the hinge increases to become k 11 ', k 22 ', k 33 ', k 44 ', k 55 ', k 66 '.

[0088] As Figure 10 shown, when the moving platform 16 is in the initial position, after moving 5 mm along the y-axis and finally 5 mm along the x-axis, at these three different positions, on the premise of keeping the current position of the moving platform unchanged, the loading states of each branch chain can be adjusted by re-distributing the torque in the null space. This adjustment allows the flexible hinge to change from the non-switching state of the deformation in Figure 9 (b) to the switching state of the deformation in Figure 9 (c) by adding additional forces and torques through the linear actuator. At this time, due to k ii ' > k ii , the stiffness of the flexible hinge is improved, and the local stiffness of the mechanism is significantly improved, thereby increasing the overall output stiffness of the mechanism. In addition, the synergistic effect between the branch chains allows the deformation states of different branch chains to compensate for each other, thereby maintaining the position stability of the moving platform. By optimizing the internal force distribution of each branch chain, the adjustment of the local and overall stiffness can be achieved.

[0089] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0090] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state, including a moving platform, characterized in that, Four static platforms are circumferentially arranged on the moving platform, and linkages are arranged between the static platforms and the moving platform; each linkage includes two groups of flexible hinges, and the two groups of flexible hinges are relatively fixed to the static platform and the moving platform respectively; the number of flexible hinges in each group is two, and they are distributed vertically, and the two flexible hinges in each group are fixed by a connecting piece; the two connecting pieces are connected by a linear actuator, and the distance between the static platform and the moving platform can be adjusted; When the flexible hinge is subjected to external force and torque, it deforms and can realize the relative torsion between the static platform and the moving platform.

2. The variable-stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 1, wherein The flexible hinge includes two sector-shaped connecting regions and two sector-shaped hollow regions that are symmetrically distributed in the circumferential direction, and the sector-shaped connecting regions and the sector-shaped hollow regions are arranged at intervals; a fixed end is respectively arranged at both ends of the sector-shaped hollow region, and the fixed end is relatively fixed to the corresponding static platform and the moving platform; the sector-shaped connecting region is fixed to the connecting piece.

3. The variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 2, characterized in that, A section one and a section four are respectively arranged at the two edges of the sector-shaped hollow region; a section three in a T shape is arranged at the hollow part in the middle of the sector-shaped hollow region, and a section two is arranged at the edge of the hollow part in the middle.

4. The variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 3, characterized in that, When the flexible hinge is subjected to the tangential force transmitted by the connecting piece, the sector-shaped connecting region deforms towards the sector-shaped hollow region, and at the same time, section one and section four also deform, and section three rotates at the hollow part in the middle; as the flexible hinge continues to deform, section three can contact section two and generate friction to increase the stiffness of the flexible hinge.

5. The variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 1, wherein, The linear actuator is fixed on one of the connecting pieces, and the push rod of the linear actuator is fixed to the other connecting piece.

6. The variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 5, characterized in that, The linear actuator is fixed to one of the connecting pieces by bolts, and the push rod of the linear actuator is fixed to the other connecting piece by bolts and nuts.

7. The variable-stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 1, wherein, A cover plate is fixed to the upper end of the static platform by means of bolt connection, and the cover plate is fixed to the flexible hinge by means of bolt connection.

8. The variable stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 1, characterized in that, Cover plates are respectively fixed by bolts at the eight corners at the upper and lower ends of the moving platform, and the flexible hinge is fixed to the cover plate by means of bolt connection.

9. The variable-stiffness planar parallel positioning platform with a flexible hinge having a switchable contact state according to claim 1, characterized in that, The material of the flexible hinge is spring steel.

10. A parallel robot, characterized in that, A variable stiffness planar parallel positioning platform having a flexible hinge with a switchable contact state according to any one of claims 1-8.

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