Parallel mechanism with just constrained kinematic chain

Abstract

A parallel mechanism containing just constrained kinematic chains comprises a fixed base, a movable platform and four branch kinematic chains between the fixed base and the movable platform, a first branch kinematic chain, a second branch kinematic chain and a third branch kinematic chain are connected to the same side face of the movable platform, and a fourth branch kinematic chain is connected to the other face, opposite to the side face, of the movable platform. The first branch kinematic chain, the third branch kinematic chain and the fourth branch kinematic chain are active kinematic chains and comprise passive telescopic assemblies and third connecting rods, the third connecting rods in the first branch kinematic chain are connected with the movable platform through rotating pairs, and the third connecting rods in the third branch kinematic chain and the fourth branch kinematic chain are connected with the movable platform through universal hinges. The second branch kinematic chain is a just constraint kinematic chain, and a second branch connecting rod I, a second branch connecting rod II and a second branch revolute pair are sequentially arranged from the fixed base to the movable platform. The mechanism is completely decoupled and has good stability and rigidity, error accumulation and transmission caused by coupling are reduced, the movement precision can be better guaranteed, and control and optimization are easy.

Description

Technical Field

[0001] The invention belongs to the field of mechanism and robot technology, and in particular relates to a parallel mechanism with a just-constrained kinematic chain. Background Art

[0002] A parallel mechanism is a closed-loop mechanical system consisting of a moving platform and a static platform connected by two or more parallel branch kinematic chains. In a parallel mechanism, each branch kinematic chain works together to achieve a specific movement of the moving platform relative to the static platform. These branch kinematic chains are usually composed of connecting rods, joints, and drivers. The parallel mechanism has unique characteristics and advantages such as high rigidity, high precision, strong load-bearing capacity, and good dynamic response. Compared with the series mechanism, the parallel mechanism has a more compact structure and can achieve complex movements in a smaller workspace. In practical applications, parallel mechanisms are widely used in industrial robots, flight simulators, medical equipment, machine tools, and other fields to meet the working requirements of high precision, high speed, and high load.

[0003] However, for most parallel mechanisms, there are still problems such as strong coupling, high control difficulty, and complex structure, which to some extent hinder the development of parallel mechanisms. Summary of the invention

[0004] The purpose of the present invention is to provide a parallel mechanism with a just-constrained kinematic chain to solve the problems of the existing mechanism, such as strong coupling, high control difficulty, and complex structure.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a parallel mechanism with a just-constrained kinematic chain, comprising a fixed base, a moving platform, and a first branch kinematic chain, a second branch kinematic chain, a third branch kinematic chain and a fourth branch kinematic chain located between the fixed base and the moving platform, the first branch kinematic chain, the second branch kinematic chain and the third branch kinematic chain are connected to the same side surface of the moving platform, and the fourth branch kinematic chain is connected to the other side of the moving platform opposite to the side surface; The first branch kinematic chain, the third branch kinematic chain and the fourth branch kinematic chain are active kinematic chains, each comprising a passive telescopic assembly and a connecting rod three, the passive telescopic assembly being formed by a connecting rod one and a connecting rod two being slidably connected, the connecting rod one being slidably connected to a fixed base, the connecting rod two being rotatably connected to the connecting rod three, the connecting rod three in the first branch kinematic chain being connected to the moving platform via a rotating pair, and the connecting rods three in the third branch kinematic chain and the fourth branch kinematic chain being connected to the moving platform via universal joints respectively; The second branch kinematic chain is a just-constrained kinematic chain, and a second branch connecting rod 1, a second branch connecting rod 2 and a second branch rotating pair are sequentially arranged from the fixed base to the moving platform; the second branch connecting rod 1 is connected to the fixed base through the second branch moving pair 1, the lower end of the second branch connecting rod 2 is connected to the second branch connecting rod 1 through the second branch moving pair 2, and the upper end of the second branch connecting rod 2 is connected to the moving platform through the second branch rotating pair; The rotation axis between the first branch motion chain and the moving platform, the rotation axis between the second branch motion chain and the moving platform, and the rotation axis between the third branch motion chain and the moving platform are in the same straight line, and the straight line is defined as x axis; x Constructing a plane based on an axis hey , among which y The axis is parallel to the moving direction of the passive telescopic component in the third branch kinematic chain on the fixed base, and the telescopic direction of the passive telescopic component in the third branch kinematic chain is parallel to the moving direction of the passive telescopic component in the third branch kinematic chain. x Axis intersects plane hey The origin o; The rotation axis between the passive telescopic component and the connecting rod 3 in the first branch kinematic chain and the rotation axis between the fourth branch kinematic chain and the moving platform are parallel to the x The rotation axis of the connecting rod at both ends of the third branch kinematic chain is parallel to the y axis; The moving direction of the second branch moving pair, the telescopic direction of the passive telescopic component in the fourth branch kinematic chain and the moving direction of the passive telescopic component in the first branch kinematic chain on the fixed base are parallel to the x axis; the telescopic direction of the passive telescopic component in the first branch kinematic chain and the passive telescopic component in the third branch kinematic chain and the moving direction of the passive telescopic component in the fourth branch kinematic chain on the fixed base are perpendicular to the plane xoy; the moving direction of the second branch moving pair is parallel to the y axis.

[0006] Furthermore, in the first branch motion chain, the link 1, link 2 and link 3 are respectively the first branch link 1, the first branch link 2 and the first branch link 3, the first branch link 1 is slidably connected to the first fixed base through the first branch moving pair 1, the first branch link 2 is slidably connected to the first branch link 1 through the first branch moving pair 2 to form the passive telescopic component, one end of the first branch link 3 is connected to the first branch link 2 through the first branch rotating pair 1, and the other end is connected to the moving platform through the first branch rotating pair 2.

[0007] Furthermore, the first branch moving pair is an active pair of the first branch kinematic chain.

[0008] Furthermore, in the third branch motion chain, the link 1, link 2 and link 3 are respectively the third branch link 1, the third branch link 2 and the third branch link 3; the third branch link 1 is slidably connected to the third fixed base through the third branch moving pair 1, the third branch link 2 is slidably connected to the third branch link 1 through the third branch moving pair 2 to form the passive telescopic component, one end of the third branch link 3 is connected to the third branch link 2 through the third branch rotating pair, and the other end is connected to the moving platform through the third branch universal hinge.

[0009] Furthermore, the third branch moving pair is an active pair of the third branch kinematic chain.

[0010] Furthermore, in the fourth branch motion chain, the link 1, link 2 and link 3 are respectively the fourth branch link 1, the fourth branch link 2 and the fourth branch link 3; the fourth branch link 1 is slidably connected to the fourth fixed base through the fourth branch moving pair 1, the fourth branch link 2 is slidably connected to the fourth branch link 1 through the fourth branch moving pair 2 to form the passive telescopic component, one end of the fourth branch link 3 is connected to the fourth branch link 2 through the fourth branch rotating pair, and the other end is connected to the moving platform through the fourth branch universal hinge.

[0011] Furthermore, the fourth branch moving pair 1 is an active pair of the fourth branch kinematic chain.

[0012] Furthermore, the active pair is driven by a linear drive mechanism.

[0013] Specifically, the linear drive mechanism is an electric cylinder, an oil cylinder or a screw mechanism.

[0014] The beneficial effects of the present invention are as follows: the present invention proposes a completely decoupled two-shift one-rotation parallel mechanism with a just-constrained kinematic chain, which can realize the movement of the moving platform along the x Towards, y Movement to and x The rotation of the axis is complete, and each motion is completely decoupled. The output motion of the moving platform corresponds to the input motion of the active pair one by one, making the active pairs of the mechanism independent of each other, reducing the error accumulation and transmission caused by coupling, and better ensuring the motion accuracy, which is easy to control and optimize.

[0015] The parallel mechanism proposed in the present invention is completely decoupled, has good stability and rigidity, and has a simple structure. It has good development prospects in the fields of parallel motion machine tools, 3-D printers, motion simulation platforms, and special processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] tú1 It is a structural schematic diagram of the parallel mechanism of the present invention; Markings in the figure: L1, first branch kinematic chain, 1-1, first branch link 1, 1-2, first branch link 2, 1-3, first branch link 3, P11, first branch moving pair 1, P12, first branch moving pair 2, R11, first branch rotation pair 1, R12, first branch rotation pair 2; L2, second branch kinematic chain, 2-1, second branch connecting rod 1, 2-2, second branch connecting rod 2, P21, second branch moving pair 1, P22, second branch moving pair 2, R21, second branch rotation pair; L3, the third branch kinematic chain, 3-1, the third branch connecting rod 1, 3-2, the third branch connecting rod 2, 3-3, the third branch connecting rod 3, P31, the third branch moving pair 1, P32, the third branch moving pair 2, R31, the third branch rotating pair, U31, the third branch universal joint; L4, fourth branch kinematic chain, 4-1, fourth branch connecting rod 1, 4-2, fourth branch connecting rod 2, 4-3, fourth branch connecting rod 3, P41, fourth branch moving pair 1, P42, fourth branch moving pair 2, R41, fourth branch rotation pair, U41, fourth branch universal joint; 5-1, first fixed base, 5-2, second fixed base, 5-3, third fixed base, 5-4, fourth fixed base, 6, moving platform; x Axis: the common line between the rotation axis of the first branch rotation pair 2 and the rotation axis of the second branch rotation pair, and parallel to the movement direction of the first branch movement pair 1; y Axis: parallel to the moving direction of the third branch moving pair. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the invention in any way.

[0019] like tú1As shown, a parallel mechanism containing a just-constrained kinematic chain comprises a first branch kinematic chain L1, a second branch kinematic chain L2, a third branch kinematic chain L3, a fourth branch kinematic chain L4, a fixed base and a moving platform 6. The fixed base is fixedly arranged and its position remains unchanged. Four fixed bases are arranged, namely the first fixed base 5-1, the second fixed base 5-2, the third fixed base 5-3 and the fourth fixed base 5-1. The four fixed bases are respectively connected to one end of the four branch kinematic chains, and the other ends of the four branch kinematic chains are connected to the moving platform 6. The first branch kinematic chain L1, the second branch kinematic chain L2 and the third branch kinematic chain L3 are connected to the same side of the moving platform 6, and the fourth branch kinematic chain L4 is connected to the other side of the moving platform 6 opposite to the side.

[0020] The composition and function of the four branch kinematic chains are described in detail below.

[0021] The first branch motion chain L1 includes a first branch link 1-1, a first branch link 2 1-2, a first branch link 3 1-3, a first branch moving pair 1 P11, a first branch moving pair 2 P12, a first branch rotation pair 1 R11 and a first branch rotation pair 2 R12. One end of the first branch link 1-1 is slidably connected to the first fixed base 5-1 through the first branch moving pair 1 P11, and the other end of the first branch link 1-1 is slidably connected to the first branch link 2 1-2 to form the first branch moving pair 2 P12. The moving direction of the first branch moving pair 2 P12 is parallel to the first branch link 1-1 and the first branch link 2 1-2, so as to realize the extension and retraction of the first branch link 2 1-2 relative to the first branch link 1. The first branch rotation pair 1 R11 is used to connect the first branch link 2 1-2 and the first branch link 3 1-3; the first branch rotation pair 2 R12 is used to connect the first branch link 3 1-3 and the moving platform 6. The rotation axes of the first branch rotation pair 1 R11 and the first branch rotation pair 2 R12 are parallel to each other and parallel to the movement direction of the first branch movement pair 1 P11.

[0022] The second branch motion chain L2 includes a second branch link 2-1, a second branch link 2-2, a second branch moving pair 1 P21, a second branch moving pair 2 P22 and a second branch rotation pair R21. The second branch link 2-1 is slidably connected to the second fixed base 5-2 through the second branch moving pair 1 P21, and the moving direction of the second branch moving pair 1 P21 is parallel to the moving direction of the first branch moving pair 1 P11. One end of the second branch link 2-2 is slidably connected to the second branch link 2-1 through the second branch moving pair 2 P22, and the moving direction of the second branch moving pair 2 P22 is perpendicular to the moving direction of the second branch moving pair 1 P21, and the other end of the second branch link 2-2 is connected to the moving platform 6 through the second branch rotation pair R21.

[0023] The third branch motion chain L3 includes a third branch link 1 3-1, a third branch link 2 3-2, a third branch link 3-3, a third branch moving pair 1 P31, a third branch moving pair 2 P32, a third branch rotation pair R31 and a third branch universal hinge U31. One end of the third branch link 1 3-1 is slidably connected to the third fixed base 5-3 through the third branch moving pair 1 P31, and the other end of the third branch link 1 3-1 is slidably connected to the third branch link 2 3-2 to form the third branch moving pair 2 P32, and the third branch moving pair 2 P32 is used to realize the extension and retraction of the third branch link 2 3-2 relative to the third branch link 1 3-1. The third branch rotation pair R31 is used to connect the third branch link 2 3-2 and the third branch link 3 3-3, and the rotation axis of the third branch rotation pair R31 is parallel to the moving direction of the third branch moving pair 1 P31. One side of the third branch universal hinge U31 is connected to the end of the third branch connecting rod three 3-3, and the other side is connected to the side of the moving platform 6. The moving direction of the third branch moving pair P31 is perpendicular to the moving direction of the first branch moving pair P11. The third branch universal hinge U31 has two mutually perpendicular rotating shafts, namely the first rotating shaft and the second rotating shaft. One end of the first rotating shaft is connected to the third branch connecting rod three 3-3, and one end of the second rotating shaft is connected to the moving platform 6. The rotation axis of the first rotating shaft is parallel to the rotation axis of the third branch rotating pair R31.

[0024] The fourth branch kinematic chain L4 includes a fourth branch link 1 4-1, a fourth branch link 2 4-2, a fourth branch link 3 4-3, a fourth branch moving pair 1 P41, a fourth branch moving pair 2 P42, a fourth branch rotation pair R41 and a fourth branch universal joint U41. One end of the fourth branch link 1 4-1 is slidably arranged on the fourth fixed base 5-4 through the fourth branch moving pair 1 P41, and the other end of the fourth branch link 1 4-1 is slidably arranged with the fourth branch link 2 4-2 to form the fourth branch moving pair 2 P42. The fourth branch rotation pair R41 is used to connect the fourth branch link 2 4-2 and the fourth branch link 3 4-3, one end of the fourth branch universal joint U41 is connected to the fourth branch link 3 4-3, and the other end of the fourth branch universal joint U41 is connected to the moving platform 6. The moving direction of the fourth branch moving pair 1 P41 is parallel to the moving directions of the third branch moving pair 2 P32 and the first branch moving pair 2 P12. The moving direction of the fourth branch movable pair 2 P42 is parallel to the moving direction of the first branch movable pair 1 P11 and the second branch movable pair 1 P21. The fourth branch universal joint U41 is provided with two mutually perpendicular rotating shafts, namely the third rotating shaft and the fourth rotating shaft. In the fourth branch universal joint U41, the part where the third rotating shaft is provided is connected to the fourth branch connecting rod 3 4-3, the part where the fourth rotating shaft is provided is connected to the moving platform 6, and the third rotating shaft is parallel to the rotating axis of the fourth branch rotating pair R41.

[0025] The rotation axis of the first branch rotation pair R12 of the first branch motion chain L1, the rotation axis of the second branch rotation pair R21 of the second branch motion chain L2, and the rotation axis of the second rotation axis of the third branch universal joint U31 in the third branch motion chain L3 are collinear. Let their common line be x The first branch rotation pair R12, the second branch rotation pair R21 and the third branch universal joint U31 are sequentially connected to the same side of the moving platform 6. The fourth branch universal joint U41 of the fourth branch kinematic chain L4 is connected to the opposite side of the above side, and the axis of the fourth rotating shaft in the fourth branch universal joint U41 is connected to the same side of the moving platform 6. x Axis parallel.

[0026] As mentioned x Constructing planes based on axes hey The moving direction of the third branch moving pair P32 is the same as that of the x The axes intersect at the origin o, y The axis is parallel to the moving direction of the third branch moving pair P31. The rotation axis of the first branch rotating pair R11 is parallel to the xThe rotation axis of the third branch rotation pair R31 and the rotation axis of the first rotation axis of the third branch universal joint U31 are parallel to the y The rotation axis of the fourth branch rotation pair R41 and the rotation axis of the third rotation axis of the fourth branch universal joint U41 are perpendicular to the plane hey .

[0027] The moving direction of the first branch moving pair P11 of the first branch motion chain L1, the moving direction of the third branch moving pair P31 of the third branch motion chain L3, and the moving direction of the fourth branch moving pair P41 of the fourth branch motion chain L4 are perpendicular to each other and are orthogonally distributed in space. The moving direction of the second branch moving pair P21 of the second branch motion chain L2 and the moving direction of the fourth branch moving pair P42 of the fourth branch motion chain L4 are both parallel to the moving direction of the first branch moving pair P11 of the first branch motion chain L1, and are also parallel to the x-axis. The moving direction of the first branch moving pair P12 of the first branch motion chain L1 and the moving direction of the third branch moving pair P32 of the third branch motion chain L3 are both parallel to the moving direction of the fourth branch moving pair P41 of the fourth branch motion chain L4, and are also perpendicular to the plane xoy. The moving direction of the second branch moving pair 2 P22 of the second branch motion chain L2 is parallel to the moving direction of the third branch moving pair 1 P31 of the third branch motion chain L3, and are also parallel to the y-axis.

[0028] In order to realize the relative position relationship of each branch kinematic chain in space, based on tú1 As shown in the direction of, the first fixed base 5-1, the second fixed base 5-2 and the third fixed base 5-3 are all arranged horizontally, and the fourth fixed base 5-4 is arranged vertically. On this basis, the first branch connecting rod 1-1 is arranged vertically perpendicular to the first fixed base 5-1; the second branch connecting rod 2-1 is perpendicular to the second fixed base 5-2 and arranged horizontally, and the second branch connecting rod 2-1 is parallel to the first fixed base 5-2. y The second branch link 2-2 is vertically arranged perpendicular to the second branch link 2-1; the third branch link 3-1 is vertically arranged perpendicular to the third fixed base 5-3; the fourth branch link 4-1 is horizontally arranged perpendicular to the fourth fixed base 5-4 and parallel to the x axis.

[0029] It is understandable that the vertical or horizontal arrangement of the above structures is just a parallel mechanism according to tú1As a result of arranging the parallel mechanism in the direction shown in the figure, in other embodiments, when the arrangement direction of the fixed base changes, such as rotating the parallel mechanism as a whole clockwise or counterclockwise to any angle, the direction of the corresponding connecting rod and the kinematic chain will also change accordingly. hey Based on the principle of keeping each joint and plane hey The relative position relationship.

[0030] In the parallel mechanism, the second branch kinematic chain L2 is a just-constrained kinematic chain without an active pair, which is used to constrain the moving platform 6 to move parallel to z The direction of the axis movement and the constraint of the moving platform around y Axis or around z The rotation of the shaft z Axis perpendicular to plane hey , and with the plane hey shared origin o The active pair in the first branch motion chain L1 is the first branch moving pair P11, the active pair in the third branch motion chain L3 is the third branch moving pair P31, and the active pair in the fourth branch motion chain L4 is the fourth branch moving pair P41.

[0031] The active pairs in each branch kinematic chain are driven by electric cylinders. When the first branch kinematic chain L1 is driven, the moving platform 6 can be moved parallel to x When the third branch kinematic chain L3 is driven, the moving platform 6 can be moved parallel to y When the fourth branch kinematic chain L4 is driven, the moving platform 6 can be moved around x The axis rotates up and down; thereby realizing the two-dimensional movement and one-dimensional rotation of the dynamic platform 6 in space through the cooperation of each branch motion chain.

[0032] In other embodiments, the active pair may also be driven by a linear drive mechanism such as an oil cylinder, a screw mechanism, etc. that can achieve linear movement.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art should understand that the specific implementation modes of the present invention may be modified or replaced by equivalents with reference to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the pending claims.

Claims

1. A parallel mechanism with a just-constrained kinematic chain, comprising a fixed base, a moving platform (6), and a first branch kinematic chain (L1), a second branch kinematic chain (L2), a third branch kinematic chain (L3), and a fourth branch kinematic chain (L4) located between the fixed base and the moving platform (6), characterized in that: The first branch kinematic chain (L1), the second branch kinematic chain (L2) and the third branch kinematic chain (L3) are connected to the same side of the moving platform (6), and the fourth branch kinematic chain (L4) is connected to the other side of the moving platform (6) opposite to the side; The first branch kinematic chain (L1), the third branch kinematic chain (L3) and the fourth branch kinematic chain (L4) are active kinematic chains, each comprising a passive telescopic assembly and a connecting rod three, the passive telescopic assembly being formed by a connecting rod one and a connecting rod two being slidably connected, the connecting rod one being slidably connected to a fixed base, the connecting rod two being rotatably connected to the connecting rod three, the connecting rod three in the first branch kinematic chain (L1) being connected to a moving platform (6) via a rotating pair, and the connecting rods three in the third branch kinematic chain (L3) and the fourth branch kinematic chain (L4) being connected to the moving platform (6) via universal joints respectively; The second branch kinematic chain (L2) is a just-constrained kinematic chain, and is provided with a second branch connecting rod 1 (2-1), a second branch connecting rod 2 (2-2) and a second branch rotating pair (R21) in sequence from the fixed base to the moving platform (6); the second branch connecting rod 1 (2-1) is connected to the fixed base via a second branch moving pair 1 (P21), the lower end of the second branch connecting rod 2 (2-2) is connected to the second branch connecting rod 1 (2-1) via a second branch moving pair 2 (P22), and the upper end of the second branch connecting rod 2 (2-2) is connected to the moving platform (6) via a second branch rotating pair (R21); The rotation axis between the first branch motion chain (L1) and the moving platform (6), the rotation axis between the second branch motion chain (L2) and the moving platform (6), and the rotation axis between the third branch motion chain (L3) and the moving platform (6) are located in the same straight line, and the straight line is defined as the x-axis; a plane xoy is constructed on the basis of the x-axis, wherein the y-axis is parallel to the moving direction of the passive telescopic component in the third branch motion chain (L3) on the fixed base, and the telescopic direction of the passive telescopic component in the third branch motion chain (L3) intersects with the x-axis at the origin o of the plane xoy; The rotation axis between the passive telescopic component and the connecting rod 3 in the first branch kinematic chain (L1), and the rotation axis between the fourth branch kinematic chain (L4) and the moving platform (6) are parallel to the x-axis; the rotation axes at both ends of the connecting rod 3 in the third branch kinematic chain (L3) are parallel to the y-axis; The moving direction of the second branch mobile pair 1 (P21), the telescopic direction of the passive telescopic component in the fourth branch motion chain (L4), and the moving direction of the passive telescopic component in the first branch motion chain (L1) on the fixed base are parallel to the x-axis; the telescopic direction of the passive telescopic component in the first branch motion chain (L1) and the passive telescopic component in the third branch motion chain (L3) and the moving direction of the passive telescopic component in the fourth branch motion chain (L4) on the fixed base are all perpendicular to the plane xoy; the moving direction of the second branch mobile pair 2 (P22) is parallel to the y-axis.

2. The parallel mechanism with just-constrained kinematic chain according to claim 1, characterized in that: In the first branch kinematic chain (L1), the link 1, link 2 and link 3 are respectively the first branch link 1 (1-1), the first branch link 2 (1-2) and the first branch link 3 (1-3); the first branch link 1 (1-1) is slidably connected to the first fixed base (5-1) via the first branch movable joint 1 (P11); the first branch link 2 (1-2) is slidably connected to the first branch link 1 (1-1) via the first branch movable joint 2 (P12) to form the passive telescopic component; one end of the first branch link 3 (1-3) is connected to the first branch link 2 (1-2) via the first branch rotating joint 1 (R11); and the other end is connected to the moving platform (6) via the first branch rotating joint 2 (R12).

3. The parallel mechanism with just-constrained kinematic chain according to claim 2, characterized in that: The first branch moving pair 1 (P11) is an active pair of the first branch kinematic chain (L1).

4. The parallel mechanism with just-constrained kinematic chain according to claim 1, characterized in that: In the third branch kinematic chain (L3), the link 1, link 2 and link 3 are respectively the third branch link 1 (3-1), the third branch link 2 (3-2) and the third branch link 3 (3-3); the third branch link 1 (3-1) is slidably connected to the third fixed base (5-3) via the third branch movable pair 1 (P31), the third branch link 2 (3-2) is slidably connected to the third branch link 1 (3-1) via the third branch movable pair 2 (P32) to form the passive telescopic component, one end of the third branch link 3 (3-3) is connected to the third branch link 2 (3-2) via the third branch rotating pair (R31), and the other end is connected to the moving platform via the third branch universal joint (U31).

5. The parallel mechanism with just-constrained kinematic chain according to claim 4, characterized in that: The third branch moving pair 1 (P31) is an active pair of the third branch kinematic chain (L3).

6. The parallel mechanism with just-constrained kinematic chain according to claim 1, characterized in that: In the fourth branch kinematic chain (L4), the link 1, link 2 and link 3 are respectively the fourth branch link 1 (4-1), the fourth branch link 2 (4-2) and the fourth branch link 3 (4-3); the fourth branch link 1 (4-1) is slidably connected to the fourth fixed base (5-4) via the fourth branch movable pair 1 (P41), the fourth branch link 2 (4-2) is slidably connected to the fourth branch link 1 (4-1) via the fourth branch movable pair 2 (P42) to form the passive telescopic component, and one end of the fourth branch link 3 (4-3) is connected to the fourth branch link 2 (4-2) via the fourth branch rotating pair (R41), and the other end is connected to the moving platform (6) via the fourth branch universal joint (U41).

7. The parallel mechanism with just-constrained kinematic chain according to claim 6, characterized in that: The fourth branch moving pair 1 (P41) is an active pair of the fourth branch kinematic chain (L4).

8. The parallel mechanism with just-constrained kinematic chain according to any one of claims 3, 5 and 7, characterized in that: The active pair is driven by a linear drive mechanism.

9. The parallel mechanism with just-constrained kinematic chain according to claim 8, characterized in that: The linear drive mechanism is an electric cylinder, an oil cylinder or a screw mechanism.

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