Configuration method of heavy load force-motion coupling parallel mechanism

Abstract

The invention relates to a heavy load force-motion coupling parallel mechanism configuration method, which comprises the following steps of S1, determining a branch chain optimal bearing criterion of a parallel mechanism based on a spinor theory and a parallel mechanism force balance condition: keeping a driving force provided by a branch chain consistent with an externally applied load direction; s2, determining the driving minimum load criterion of the parallel mechanism on the basis that the pole position of the connecting rod mechanism has the force increasing effect, wherein the driving force provided by the driving joints is orthogonal to the driving force provided by the branch chains in direction; s3, determining an optimal force bearing criterion of the parallel mechanism in combination with a branch chain optimal bearing criterion and a driving minimum load criterion; s4, the optimal force bearing criterion and the motion constraint spinor of the parallel mechanism are coupled, and a heavy load force-motion coupling type comprehensive process is deduced and put forward; and S5, carrying out branch synthesis and structure synthesis on the parallel mechanism containing the spatial rotation motion. The invention provides a new method for synthesizing the heavy-load parallel mechanism, so that the application prospect of the parallel mechanism under the heavy-load working condition is further improved.

Description

Technical Field

[0001] The present invention relates to the field of parallel mechanism configuration synthesis, and more specifically, to a heavy-load force-motion coupling parallel mechanism configuration method. Background Art

[0002] The multi-chain closed-loop structure of the parallel mechanism has the advantages of strong load-bearing capacity, high rigidity and high precision, and is widely used in handling, packaging, forming and other fields. The configuration synthesis of the parallel mechanism includes type synthesis and scale synthesis, which is the basis for the research and development and design of the parallel mechanism to meet the motion requirements, achieve performance requirements and improve the dynamic performance. At present, a variety of configuration synthesis methods have been proposed by scholars: in terms of type synthesis, they mainly include the method based on the screw theory, displacement group theory, virtual loop method and POC set method; in terms of scale synthesis, they mainly include performance maps and parameter optimization methods based on the objective function. However, the current design of parallel mechanisms generally starts with type synthesis based on motion modes, and then optimizes parameters according to performance requirements. In other words, the type synthesis and scale synthesis of the parallel mechanism are performed separately. This separation makes it difficult to determine the performance of the parallel mechanism such as the load-bearing capacity in the type synthesis stage, and it is difficult to achieve the simultaneous optimization of the mechanism configuration and scale, which limits the performance improvement of the existing parallel mechanism. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a configuration method of a heavy-load force-motion coupling parallel mechanism, which can improve the performance of the parallel mechanism.

[0004] The technical solution adopted by the present invention to solve the technical problem is: constructing a heavy-load force-motion coupling parallel mechanism configuration method, comprising the following steps:

[0005] S1. Based on the screw theory and the force balance condition of the parallel mechanism, the optimal load-bearing criterion of the branch chain of the parallel mechanism is determined: the driving force provided by the branch chain is consistent with the direction of the externally applied load;

[0006] S2. Based on the force-increasing effect of the connecting rod mechanism at the extreme position, the minimum driving load criterion of the parallel mechanism is determined: the driving force provided by the driving joint is orthogonal to the driving force provided by the branch chain;

[0007] S3. Determine the optimal force bearing criterion of the parallel mechanism by combining the optimal bearing criterion of the branch chain and the minimum driving load criterion;

[0008] S4, coupled parallel mechanism optimal force bearing criterion and motion constraint screw, derived and proposed heavy load force-motion coupling type comprehensive process;

[0009] S5. Branch synthesis and structural synthesis were carried out on the parallel mechanism involving spatial rotational motion.

[0010] In the above scheme, in step S1, the motion / force of the parallel mechanism moving platform is represented as the intersection of the motions of each branch chain.

[0011]

[0012] In the formula, ξ ij represents the instantaneous velocity amplitude of the jth kinematic joint on the i-th limb, m S ij represents the instantaneous motion spin of the jth kinematic pair on the i-th limb, express m S ij The unit spin of ; f S ri is the instantaneous force screw of the ith branch, is the instantaneous reciprocal spinor of the kth joint of the ith branch acting on the mobile platform, and They are f S ri and The unit spinor, f i Force screw f S ri The amplitude, f ik is the instantaneous reciprocal spinor The amplitude of the moving platform is expressed as the reciprocal product of its motion spinor and force spinor:

[0013]

[0014] In the formula, the force rotation f S ri Provided by the branch actuator, it is directly used to offset the resistance / resistance torque that hinders the motion of the parallel mechanism, which is solved according to the following formula;

[0015]

[0016] Force Rotation is the constraint reaction force generated by the branch's geometric constraints, the force screw The power provided to the motion platform is zero; Formula (3) is rewritten as,

[0017]

[0018] The optimal load-bearing criterion for determining the branch chain of the parallel mechanism is:

[0019]

[0020] In the above scheme, in step S2, when the branch driven by the rotary joint is at the limit position, the force rotation amount f S riThe kinematic rotation of the driven joint m S i1 Coplanar in space; when the branch driven by the mobile joint is in the extreme position, the force rotation f S ri The kinematic rotation of the driven joint m S i1 Coplanar and orthogonal, the extreme positions of the branches are defined as:

[0021]

[0022] In the above scheme, in step S3, the optimal load-bearing condition of the branch under heavy load conditions satisfies the following formula:

[0023]

[0024] In the above scheme, in step S4, the generalized motion subspace of the parallel mechanism n S is expressed by the moving platform motion screw system:

[0025]

[0026] In the formula, (S1, S2, ..., S n ) represents a set of linearly independent unit spinors, n S represents an n-order spinor system, which is related to a set of linearly independent spinors (S1, S2, ..., S n ) is the set of all the spinors that are linearly related to each other. The superscript “n” represents the degree of freedom of the parallel mechanism motion platform. The constrained spinor system of the motion platform is expressed as:

[0027]

[0028] Based on the set union operation satisfied by the parallel mechanism branch constraint screw system and the moving platform constraint screw system: The branched constrained spinor system is expressed as:

[0029]

[0030] Substituting the optimal load-bearing condition into the branch's constrained screw system, the branch's constrained screw system that satisfies the optimal load-bearing condition is rewritten as:

[0031]

[0032]

[0033] The branched kinematic screw system is solved according to the following equation:

[0034]

[0035] On this basis, various types of parallel mechanism branches with optimal load-bearing conditions are generated through the linear combination of branch motion rotary quantities, and a parallel mechanism that meets the motion requirements and has excellent load-bearing performance is obtained.

[0036] In the above scheme, in step S5, it is assumed that the generalized force applied to the moving platform is expressed as: f S p =(s w ; r w ×s w ),r w =(l1 m1 n1) T , then the force screw is expressed as:

[0037]

[0038] According to formula (19), the corresponding branch motion spinor system is expressed as:

[0039]

[0040] In the formula, a i , b i and c i represents the proportionality coefficient, satisfying |a i |+|b i |≠0, and c i ≠0, ⊥ s w Indicates orthogonal to s w vector; further, according to formula (21), the specific branch motion spinor system corresponding to the specific external force spinor is derived, assuming that, f S ri =(z; r e ×z),r e =[l e m e n e ] T ;

[0041]

[0042] By linearly combining the branch motion spinors in equation (22), we can obtain the branch that meets the motion requirements.

[0043] The above scheme also includes step S6, which is to solve the problem of the integrated parallel mechanism being located at a singular position by using a scale synthesis method based on the task space.

[0044] In the above scheme, in step S6, the parallel connection is scaled to avoid singularities, and the relationship between the motion space and the carrying capacity near singularities is established; the relationship between input and output is obtained using the vector closure method. Therefore, it can be reasonably assumed that the input-output relationship of the parallel mechanism is:

[0045]

[0046] In the formula, Indicates the input speed of each branch driving joint, Indicates the output speed of the moving platform; under heavy load conditions, the rotation m S ij，j≠1 and spinor f S ri If it is an intersection relationship, the branch structure parameters satisfy the following constraints:

[0047]

[0048] In the formula, represents the end point of branch i, a ij Represents the position vector of the jth joint in branch i; combined with the structural parameter constraints, input-output relationship and workspace, some initial parameters of the branch are calculated.

[0049] The heavy-load force-motion coupling parallel mechanism configuration method of the present invention has the following beneficial effects:

[0050] 1. The present invention proposes a new heavy-load force-motion coupling synthesis method by coupling the optimal force bearing criterion and motion constraint of the parallel mechanism, and the synthesized parallel mechanism has excellent load-bearing performance;

[0051] 2. The 6-PHSS parallel mechanism designed by the present invention achieves a high effective load output-input ratio of more than 25. Compared with the Stewart platform (6-UPS parallel mechanism) designed by the traditional method, the maximum forces of the actuator and the connecting rod are significantly reduced by 80% and 10%, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0053] Figure 1 It is a schematic diagram of the branch configuration of the 3R3T parallel mechanism with the optimal load-bearing criterion;

[0054] Figure 2 It is a schematic diagram of the branch configuration of the 3R parallel mechanism with the optimal load-bearing criterion;

[0055] Figure 3It is a schematic diagram of the branch configuration of the 3R1T parallel mechanism with the optimal load-bearing criterion;

[0056] Figure 4 It is a schematic diagram of the branch configuration of the 3R2T parallel mechanism with the optimal load-bearing criterion;

[0057] Figure 5 It is a basic structural diagram of the 6-PHSS parallel mechanism;

[0058] Figure 6 It is the force diagram of the connecting rod of the 6-PHSS parallel mechanism;

[0059] Figure 7 It is the force diagram of the 6-PH SS parallel mechanism actuator;

[0060] Figure 8 It is a schematic diagram of the connecting rod force of the 6-UPS parallel mechanism. DETAILED DESCRIPTION

[0061] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0062] like Figure 1 As shown, the configuration method of the heavy-load force-motion coupling parallel mechanism of the present invention includes:

[0063] S1. Based on the screw theory and the force balance condition of the parallel mechanism, the optimal load-bearing criterion of the branch chain of the parallel mechanism is derived and defined: the driving force provided by the branch chain is consistent with the direction of the externally applied load. The motion / force of the parallel mechanism dynamic platform can be expressed as the intersection of the motions of each branch chain.

[0064]

[0065] In the formula, ξ ij represents the instantaneous velocity amplitude of the jth kinematic joint on the i-th limb, m S ij represents the instantaneous motion spin of the jth kinematic pair on the i-th limb, express m S ij The unit spin of ; f S ri is the instantaneous force screw of the ith branch, is the instantaneous reciprocal spinor of the kth joint of the ith branch acting on the mobile platform, and They are f S ri and The unit spinor, f i Force screw f S riThe amplitude, f ik is the instantaneous reciprocal spinor The instantaneous power of the moving platform can be expressed by the reciprocal product of its motion spinor and force spinor,

[0066]

[0067] In the formula, the force rotation f S ri Provided by the branch actuator, it is directly used to offset the resistance / resistance torque that hinders the motion of the parallel mechanism, which can be solved according to the following formula (assuming that the first joint is the driving joint of the limb),

[0068]

[0069] Force Rotation It is the constraint reaction force generated by the geometric constraints of the branch, which flows through the joints and connecting rods in the branch to the base without hindering the movement of the mechanism. The power provided to the motion platform is zero. Equation (3) can be rewritten as:

[0070]

[0071] From formula (5), we can see that under the same structure and size, the force torque f S ri The closer the direction is to the external force direction, the greater the load-bearing capacity of the parallel mechanism. This condition is defined as the optimal load-bearing criterion of the branch chain of the parallel mechanism, which can be expressed as follows:

[0072]

[0073] S2. Based on the force-amplifying effect at the extreme position of the connecting rod mechanism, the minimum driving load criterion of the parallel mechanism is derived and defined: the driving force provided by the driving joint is orthogonal to the driving force provided by the branch chain. Similar to the geometric characteristics of the connecting rod mechanism, the extreme positions of the parallel mechanism can also be determined by similar force-amplifying effects. The limbs of the parallel mechanism are usually driven by revolute joints (representing full-circle rotation) or mobile joints (representing alternating motion). Within one rotation cycle of the actuator joint, the branch driven by the revolute joint has two extreme positions, while the branch driven by the mobile joint has one extreme position. This feature is independent of the direction of the branch and the position of the driving joint on the branch. When the branch driven by the revolute joint is in the extreme position, the force rotation amount f S ri The kinematic rotation of the driven joint m S i1 Coplanar in space; when the branch driven by the mobile joint is in the extreme position, the force rotation f S ri The kinematic rotation of the driven jointm S i1 are coplanar and orthogonal. Therefore, the extreme positions of the branches can be defined as,

[0074]

[0075] S3. Combining the branch chain optimal load-bearing criterion and the driving minimum load criterion, the optimal force load-bearing criterion of the parallel mechanism is proposed. Combining formulas (5) and (7), the optimal load-bearing condition of the branch under heavy load conditions satisfies the following formula:

[0076]

[0077] Therefore, when the motion mode and external force of the parallel mechanism are known, the limb motion screw system can be reconstructed according to the optimal load-bearing condition of equation (8).

[0078] S4. The optimal force bearing criterion and motion constraint screw of the coupled parallel mechanism are used to derive the heavy load force-motion coupling synthesis process. The generalized motion subspace of the parallel mechanism n S can be expressed by a moving platform motion screw system,

[0079]

[0080] In the formula, (S1, S2, ..., S n ) represents a set of linearly independent unit spinors, n S represents an n-order spinor system, which is related to a set of linearly independent spinors (S1, S2, ..., S n ) is the set of all the spinors that are linearly related to each other, and the superscript “n” represents the degree of freedom of the parallel mechanism motion platform. Therefore, the constrained spinor system of the motion platform can be expressed as:

[0081]

[0082] Based on the set union operation satisfied by the parallel mechanism branch constraint screw system and the moving platform constraint screw system: The branched constrained spinor system can be expressed as,

[0083]

[0084] Furthermore, substituting the optimal load-bearing condition (Equation (8)) into the branch's constrained spinor system, the branch's constrained spinor system that satisfies the optimal load-bearing condition can be rewritten as:

[0085]

[0086] The branched kinematic screw system can be solved according to the following formula:

[0087]

[0088] On this basis, various parallel mechanism branches with optimal load-bearing conditions can be generated through the linear combination of branch motion screws. Through reasonable assembly and transmission design, a parallel mechanism that meets motion requirements and has excellent load-bearing performance can be obtained.

[0089] S5. Based on the proposed method, branch synthesis and structural synthesis of parallel mechanisms involving spatial rotational motion are performed, including 3R, 3R1T, 3R2T and 3R3T motion modes. According to step S4, it is assumed that the generalized force applied to the moving platform is expressed as: f S p =(s w ; r w ×s w ),r w =(l1 m1 n1) T , then the force twist can be expressed as:

[0090]

[0091] According to formula (19), the corresponding branch motion spinor system can be expressed as:

[0092]

[0093] In the formula, a i , b i and c i represents the proportionality coefficient, satisfying |a i |+|b i |≠0, and c i ≠0, ⊥ s w Indicates orthogonal to s w Further, according to formula (21), the specific branch motion spinor system corresponding to the specific external force spinor can be derived, assuming that f S ri =(z; r e ×z),r e =[l e m e n e ] T ,

[0094]

[0095] The branches that meet the motion requirements can be obtained by linearly combining the branch motion spinors in equation (22). Table 1 summarizes all the branches of the 3R3T parallel mechanism without considering the order of arrangement. Tables 2, 3, and 4 are the branches of 3R, 3R1T, and 3R2T respectively.

[0096] The subscript "O" in the table indicates that the axes of the joints intersect at a certain point, the subscript "E" indicates that the axes of the joints are located in the same plane, the subscript "H" indicates that the direction of the moving joint is parallel to the fixed platform, the subscript "U" indicates that two consecutive R joints intersect at a certain point, and these two joints can be replaced by U joints, and the subscript "S" indicates that the axes of three R joints intersect at the same point, and these three joints can be replaced by S joints.

[0097] Table 1 3R3T motion mode parallel mechanism branch types

[0098]

[0099] Table 2 Branch types of 3R motion mode parallel mechanism

[0100]

[0101]

[0102] Table 3 3R1T motion mode parallel mechanism branch types

[0103]

[0104] Table 4 3R2T motion mode parallel mechanism branch types

[0105]

[0106] Table 5 Parallel mechanism types

[0107]

[0108] In addition, the branching configurations shown in Tables 1 to 4 are respectively Figures 1 to 4 The branch arrangement shown in the figure corresponds to that in Figure 1. Although there are many limbs with optimal load-bearing conditions that can be used to form 3R, 3R1T, 3R2T and full-degree-of-freedom parallel mechanisms, limbs with more than three joints will affect the stiffness and stability of the parallel mechanism. Based on the above design considerations and the branch configuration under the optimal load-bearing conditions shown in Tables 1 to 4, a parallel mechanism can be generated by taking n identical branches (where n is the degree of freedom of the motion platform). Among them, (RR) in the limb U and (RRR) S The U and S joints can be used to replace them respectively, and the limbs with undriven P joints are not considered. By selecting the effective actuator input, the comprehensive results of the corresponding parallel mechanism are shown in Table 5 ( R / P represents active joint).

[0109] S6. Aiming at the problem that the synthesized parallel mechanism is located in a singular position, a scale synthesis method based on the task space is proposed. In the type synthesis based on the motion mode, the Jacobian matrix of the branch must be full rank, and the type synthesis result based on the motion mode cannot be singular. Since the optimal load-bearing condition is attached in the type synthesis, the Jacobian matrix of the branch will not be full rank, so the type synthesis result of the parallel mechanism must be singular. To this end, the parallel is scaled to avoid singularities and establish the relationship between the motion space and the load-bearing capacity under near singularities. Dimensional synthesis depends on the inverse solution of the parallel mechanism. Although the inverse solution operations of various parallel mechanisms are different, the relationship between the input and output can be obtained using the vector closure method. Therefore, it can be reasonably assumed that the input-output relationship of the parallel mechanism is:

[0110]

[0111] In the formula, Indicates the input speed of each branch driving joint, It represents the output speed of the moving platform. According to the optimal load-bearing condition, since the non-driven moving joints are usually not considered, the rotation m S ij，j≠1 The rotation of can be considered to be zero. In this case, according to the helical reciprocity geometry, the spinor f S ri and m S ij，j≠1 In addition, the direction of maximum stiffness of the structural members (passive joints and links) within a branch should be as close as possible to the axis of the branch. f S ri The direction of the twist is consistent. This usually means that the structural components are in the same straight line, because the direction of maximum stiffness of the connecting rod is usually axial. Therefore, under heavy load conditions, the twist m S ij，j≠1 and spinor f S ri If it is an intersection relationship, the branch structure parameters satisfy the following constraints:

[0112]

[0113] In the formula, represents the end point of branch i, a ij Represents the position vector of the jth joint in branch i. Combining the structural parameter constraints (Formula (24)), the input-output relationship (Formula (23)) and the workspace, some initial parameters of the branch can be calculated. It should be noted that the branch with the above parameters is in a singular position (boundary singularity, structural singularity, or both). In order to avoid the boundary singularity of the parallel mechanism, it is necessary to expand the given workspace. In order to avoid the structural singularity of the parallel mechanism, the initial distribution angle of the joint can be designed.

[0114] According to the configuration steps of the above-mentioned heavy-load force-motion coupling parallel mechanism configuration method, a nearly singular 6-P H The SS parallel mechanism realizes fixed-point swing motion and carries out parameter design and load-bearing performance evaluation. The fixed-point swing motion can be expressed as:

[0115]

[0116] In this embodiment, θ=1.5π / 180, φ=2πt, t represents time. The load during the fixed-point swing motion can be expressed as,

[0117]

[0118] 6-P H The design parameters of the SS parallel mechanism are shown in Table 6. The basic structure is as follows Figure 5 shown.

[0119] Table 6 6-P H SS PKM structural parameters

[0120] External force f(kN) 6000 External force point [200cos(2πt),200sin(2πt),0] Theoretical swing angle of moving platform θ(deg) 1.5 <![CDATA[Moving platform design swing angle θ d (deg)]]> 1.5+0.05 <![CDATA[Height h of the moving platform m (mm)]]> 530 <![CDATA[Upper ball joint distribution angle β1 (deg)]]> [10,56,130,176,250,296] <![CDATA[Upper ball joint distribution radius r b (mm)]]> 470 Lower ball joint deflection angle Δβ (deg) 10 <![CDATA[Distribution angle α of the lower ball joint i (deg)]]> {0,66,120,186,240,306} <![CDATA[Connecting rod length l i (mm)]]> 450.30 <![CDATA[Distribution angle r of the lower ball joint a (mm)]]> 568.72

[0121] According to the design parameters, 6-P H The branch forces and driver forces during the movement of the SS parallel mechanism are analyzed and calculated. Figure 6 As shown, the driver is subjected to the force Figure 7 As shown in Figure 6, the maximum forces of the connecting rod and the actuator are approximately 1610 kN and 220 kN, respectively, and the force input-output ratio exceeds 25. In addition, a traditional Stewart platform (6-UPS) with the same size as in Table 6 is established to further verify the proposed force-motion coupling mechanism synthesis method. For the 6-UPS parallel mechanism, the force of the actuator in the branch is equal to the connecting rod force generated by the motion direction of the P joint passing through the center of the U pair and the S pair. The instantaneous force on the branch of the 6-UPS parallel mechanism designed with optimized parameters during the motion process is as follows Figure 8 As shown, the maximum force of the branch and actuator is about 1810kN. In comparison, the 6-P H The SS has an 80% reduction in actuator force and a 10% reduction in maximum linkage force.

[0122] The present invention proposes a configuration method for a heavy-load force-motion coupling parallel mechanism, derives and proposes the optimal load-bearing criterion of the parallel mechanism, and proposes a new heavy-load force-motion coupling synthesis method based on the coupling load-bearing criterion and motion constraints. The parallel mechanism containing spatial rotational motion is subjected to branch synthesis and structural synthesis, including 3R, 3R1T, 3R2T and 3R3T motion modes. Aiming at the problem that the synthesized parallel mechanism is located in a singular position, a scale synthesis method based on task space is proposed. Taking the synthesized near-singular 6-PHSS parallel mechanism as an example, the performance is verified. Compared with the Stewart platform (6-UPS parallel mechanism) designed by the traditional method, the maximum force of the actuator and the limb are reduced by 80% and 10% respectively, which verifies the effectiveness of the proposed synthesis method for the heavy-load force-motion coupling parallel mechanism. The present invention provides a new method for the synthesis of heavy-load parallel mechanisms, which further improves the application prospects of parallel mechanisms under heavy-load conditions.

[0123] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for configuring a heavy-load force-motion coupling parallel mechanism, characterized in that: The following steps are involved: S1. Based on the screw theory and the force balance condition of the parallel mechanism, the optimal load-bearing criterion of the branch chain of the parallel mechanism is determined: the driving force provided by the branch chain is consistent with the direction of the externally applied load; S2. Based on the force-increasing effect of the connecting rod mechanism at the extreme position, the minimum driving load criterion of the parallel mechanism is determined: the driving force provided by the driving joint is orthogonal to the driving force provided by the branch chain; S3. Determine the optimal force bearing criterion of the parallel mechanism by combining the optimal bearing criterion of the branch chain and the minimum driving load criterion; S4, coupled parallel mechanism optimal force bearing criterion and motion constraint screw, derived and proposed heavy load force-motion coupling type comprehensive process; S5. Branch synthesis and structural synthesis were carried out on the parallel mechanism involving spatial rotational motion.

2. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 1, characterized in that: In step S1, the motion / force of the parallel mechanism moving platform is represented as the intersection of the motions of each branch chain. In the formula, ξ ij represents the instantaneous velocity amplitude of the jth kinematic joint on the i-th limb, m S ij represents the instantaneous motion spin of the jth kinematic pair on the i-th limb, express m S ij The unit spin of ; f S ri is the instantaneous force screw of the ith branch, is the instantaneous reciprocal spinor of the kth joint of the ith branch acting on the mobile platform, and They are f S ri and The unit spinor, f i Force screw f S ri The amplitude, f ik is the instantaneous reciprocal spinor The amplitude of the moving platform is expressed as the reciprocal product of its motion spinor and force spinor: In the formula, the force rotation f S ri Provided by the branch actuator, it is directly used to offset the resistance / resistance torque that hinders the motion of the parallel mechanism, which is solved according to the following formula; Force Rotation is the constraint reaction force generated by the branch's geometric constraints, the force screw The power provided to the motion platform is zero; Formula (3) is rewritten as, The optimal load-bearing criterion for determining the branch chain of the parallel mechanism is:

3. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 2, characterized in that: In step S2, when the branch driven by the rotary joint is at the limit position, the force rotation f S ri The kinematic rotation of the driven joint m S i1 Coplanar in space; when the branch driven by the mobile joint is in the extreme position, the force rotation f S ri The kinematic rotation of the driven joint m S i1 Coplanar and orthogonal, the extreme positions of the branches are defined as:

4. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 3, characterized in that: In step S3, the optimal load-bearing condition of the branch under heavy load conditions satisfies the following formula:

5. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 4, characterized in that: In step S4, the generalized motion subspace of the parallel mechanism n S is expressed by the moving platform motion screw system: In the formula, (S1, S2, ..., S n ) represents a set of linearly independent unit spinors, n S represents an n-order spinor system, which is related to a set of linearly independent spinors (S1, S2, ..., S n ) is the set of all the spinors that are linearly related to each other. The superscript "n" represents the degree of freedom of the parallel mechanism motion platform. The constrained spinor system of the motion platform is expressed as: Based on the set union operation satisfied by the parallel mechanism branch constraint screw system and the moving platform constraint screw system: The branched constrained spinor system is expressed as: Substituting the optimal load-bearing condition into the branch's constrained screw system, the branch's constrained screw system that satisfies the optimal load-bearing condition is rewritten as: The branched kinematic screw system is solved according to the following equation: On this basis, various types of parallel mechanism branches with optimal load-bearing conditions are generated through the linear combination of branch motion rotary quantities, and a parallel mechanism that meets the motion requirements and has excellent load-bearing performance is obtained.

6. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 5, characterized in that: In step S5, it is assumed that the generalized force applied to the moving platform is expressed as: f S p =(s w ; r w ×s w ),r w =(l1 m1 n1) T , then the force screw is expressed as: According to formula (19), the corresponding branch motion spinor system is expressed as: In the formula, a i 、b i and c i represents the proportionality coefficient, satisfying |a i |+|b i |≠0, and c i ≠0, ⊥ s w Indicates orthogonal to s w vector; further, according to formula (21), the specific branch motion spinor system corresponding to the specific external force spinor is derived, assuming that, f S ri =(z; r e ×z),r e =[l e m e n e ] T ; By linearly combining the branch motion spinors in equation (22), we can obtain the branch that meets the motion requirements.

7. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 6, characterized in that: The method also includes step S6, which uses a scale synthesis method based on task space to solve the problem of the integrated parallel mechanism being located at a singular position.

8. The method for configuring a heavy-load force-motion coupling parallel mechanism according to claim 7, characterized in that: In step S6, the parallel connection is scaled to avoid singularities, and the relationship between the motion space and the carrying capacity near singularities is established; the relationship between input and output is obtained using the vector closure method. Therefore, it can be reasonably assumed that the input-output relationship of the parallel mechanism is: In the formula, Indicates the input speed of each branch driving joint, Indicates the output speed of the moving platform; under heavy load conditions, the rotation m S ij，j≠1 and spinor f S ri If it is an intersection relationship, the branch structure parameters satisfy the following constraints: In the formula, represents the end point of branch i, a ij Represents the position vector of the jth joint in branch i; combined with the structural parameter constraints, input-output relationship and workspace, some initial parameters of the branch are calculated.

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