A control method for over-constrained robots based on six-dimensional force feedback solution branch force control and shaft-hole assembly system

Abstract

The application belongs to the technical field of robot control, and discloses a control method of an over-constrained robot based on six-dimensional force feedback solution branch force control and a shaft-hole assembly system. The control method comprises the following steps: building an assembly system, establishing a mapping relationship between a generalized external force of an over-constrained six-dimensional force sensor and branch forces thereof, collecting branch force signals of the over-constrained six-dimensional force sensor in real time, and solving a generalized external force suffered by an end shaft part of the over-constrained six-dimensional force sensor. The solved generalized external force of the shaft part is transmitted to a hole part, and then transmitted to an end of an over-constrained robot from the hole part. A mapping relationship between a force of the end of the over-constrained robot and branch driving forces thereof is established. The generalized external force suffered by the over-constrained robot is taken as an input parameter, and each branch driving force thereof is solved. The over-constrained robot is controlled according to the solved branch driving force to complete shaft-hole assembly. The shaft-hole assembly system comprises an over-constrained six-dimensional force sensor for fixing a shaft part and an over-constrained robot for fixing a hole part. The application can accurately solve hyperstatic branch internal forces and realize general and efficient feedback control, and can be widely applied to high-precision force control scenes such as spacecraft docking devices and precision assembly robots.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of robot control method, and relates to a control method for controlling an over-constrained robot, in particular to a control method for controlling an over-constrained robot based on six-dimensional force feedback calculation branch force. BACKGROUND

[0002] Over-constrained structures play an important role in high-end equipment manufacturing fields such as aerospace and precision detection due to their high stiffness, high bearing capacity and superior motion accuracy. For example, in order to ensure the stability of force transmission during space docking, the end effector of a space manipulator often adopts an over-constrained configuration, and in the mechanical property testing of spacecraft parts, an over-constrained six-dimensional force sensor is also widely used due to its high reliability, and the number of branches is usually more than six to improve the measurement redundancy. However, the superstatic problem caused by the introduction of redundant constraints becomes a key bottleneck that hinders the full play of the performance of such structures, and the core difficulty lies in how to accurately calculate and control the internal force of each branch.

[0003] In the prior art, the control method for over-constrained structures is mostly based on the assumption of statically determinate structure. When dealing with superstatic systems with more than six branches, the branch force cannot be directly solved by relying only on static equilibrium equations, and such methods often ignore the decisive influence of branch stiffness anisotropy on internal force distribution, which directly leads to a decrease in the accuracy of branch force information input by the control system and makes it difficult to achieve effective dynamic adjustment. Especially under high-speed motion or variable load working conditions, the internal force distribution of the system is prone to be seriously uneven, which may induce vibration and local stress concentration, and even threaten the safety of the structure. In addition, the existing technology has serious lack of universality. For over-constrained structures with different branch layouts or configurations, a lot of effort is often needed to re-derive complex mechanical models and design specific control strategies, which not only greatly increases the development cost and time cycle of engineering applications, but also cannot guarantee the reliability and consistency of different solutions. SUMMARY

[0004] The purpose of the present application is to provide a control method for controlling an over-constrained robot based on six-dimensional force feedback calculation branch force and a shaft hole assembly system, so as to achieve branch force control through force feedback calculation and ensure assembly precision and stability.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0006] A control method for controlling an over-constrained robot based on six-dimensional force feedback calculation branch force, comprising the following steps:

[0007] S1, build an assembly system comprising an over-constrained six-dimensional force sensor, a shaft part, an over-constrained robot and a hole part, in which the shaft part is assembled at the end of the over-constrained six-dimensional force sensor, and the hole part is assembled at the end of the over-constrained robot;

[0008] S2, establish a mapping relationship between the generalized external force of the over-constrained six-dimensional force sensor and the branch force thereof;

[0009] S3, collect the branch force signal of the over-constrained six-dimensional force sensor in real time, and solve the generalized external force of the shaft part at the end of the over-constrained six-dimensional force sensor;

[0010] S4, transmit the solved generalized external force of the shaft part to the hole part through action and reaction, and then transmit the force to the end of the over-constrained robot;

[0011] S5, establish a mapping relationship between the force at the end of the over-constrained robot and the branch driving force thereof;

[0012] S6, take the generalized external force of the over-constrained robot as an input parameter, and solve the branch driving force thereof;

[0013] S7, control the over-constrained robot to complete the shaft-hole assembly according to the solved branch driving force of the over-constrained robot.

[0014] As a limitation of the application, in S2, the mapping relationship is established based on the displacement coordination equation and the static force balance equation, and satisfies the following mathematical model:

[0015] ;

[0016] Wherein, is the over-determined branch internal force of the S-shaped tension-compression force sensor in the over-constrained six-dimensional force sensor under the generalized external force , δ is the over-determined branch flexibility coefficient matrix, is the deformation of the No. 1 branch to the No. n-6 branch in the force direction when the S-shaped tension-compression force sensor in the over-constrained six-dimensional force sensor is only subjected to external force after the over-constrained branch is disconnected;

[0017] The mapping relationship is: Wherein, is the generalized external force of the over-constrained six-dimensional force sensor, is the branch force on each branch of the over-constrained six-dimensional force sensor, is the influence matrix between the generalized external force of the over-constrained six-dimensional force sensor and the branch force thereof.

[0018] As another limitation of the application, in S5, the mapping relationship between the force at the end of the over-constrained robot and the branch driving force thereof is: wherein, is a branch driving force of the over-constrained robot for each branch, is a generalized external force received by the over-constrained robot, is an influence matrix between the generalized external force received by the over-constrained robot and the branch driving force thereof.

[0019] An axis-hole assembly system based on six-dimensional force feedback for solving branch force, comprising an over-constrained six-dimensional force sensor for fixing an axis part and an over-constrained robot for fixing a hole part, the over-constrained six-dimensional force sensor drives the axis part to move and transmits force to the hole part through action and reaction, and the over-constrained robot drives the hole part to move by using the control method for controlling the over-constrained robot based on the six-dimensional force feedback for solving branch force.

[0020] As a limitation of the axis-hole assembly system based on six-dimensional force feedback for solving branch force, the over-constrained robot comprises an upper platform, a middle platform and a lower platform, the hole part is assembled on the upper platform, a variable stiffness driving structure is assembled between the upper platform and the middle platform and between the middle platform and the lower platform, the variable stiffness driving structure comprises at least three UPS branch chains and a variable stiffness branch chain, the variable stiffness branch chain is arranged in the middle, and the UPS branch chains are uniformly arranged on the circumference of the variable stiffness branch chain, wherein the UPS branch chains are used to receive the generalized external force transmitted by the hole part, to obtain each branch driving force after solving, and to re-act on the hole part through the UPS branch chains, and the variable stiffness branch chain is used to make the UPS branch chains move smoothly.

[0021] As a further limitation of the axis-hole assembly system based on six-dimensional force feedback for solving branch force, the variable stiffness branch chain comprises a connecting piece, an extension rod, a spring, a connecting pipe and a variable stiffness joint, the extension rod is fixedly connected with the connecting piece, the connecting pipe is fixedly connected with the variable stiffness joint, the spring is arranged in the connecting pipe, the extension rod is inserted into the connecting rod, and the rod end of the extension rod abuts against one end of the spring.

[0022] As a further limitation of the axis-hole assembly system based on six-dimensional force feedback for solving branch force, the variable stiffness joint comprises a bearing module, a hooke joint, a variable stiffness shaft and three main-passive variable stiffness modules, the hooke joint is rotatably arranged on the bearing module through a first connecting shaft, two main-passive variable stiffness modules are connected with the hooke joint through a second connecting shaft, the first connecting shaft and the second connecting shaft are arranged perpendicularly, the variable stiffness shaft is fixedly arranged on the hooke joint, and the third main-passive variable stiffness module is connected with the variable stiffness shaft.

[0023] Compared with the prior art, the technical progress achieved by the present application is that:

[0024] The application is based on displacement compatibility equation and static equilibrium equation, constructs a mathematical mapping model of branch force of over-constrained six-dimensional force sensor and generalized external force borne by the branch force, calculates the generalized external force borne by the shaft part through collecting branch force signals of the over-constrained six-dimensional force sensor and using the mapping model, transmits the external force to the end of the over-constrained robot according to the action and reaction law to obtain the generalized external force borne by the over-constrained robot; then, the mapping relationship between the end force and the branch driving force of the over-constrained robot is established according to the structural characteristics of the over-constrained robot, the branch force is calculated with the generalized external force borne by the over-constrained robot as input, and finally the shaft hole assembly is completed by controlling the over-constrained robot to drive the end hole part and the shaft part according to the calculated branch force. The method does not need to add sensors to the branches of the over-constrained robot, realizes branch force control through force feedback calculation, ensures assembly accuracy and stability, uses the action and reaction law to enhance the stiffness and flexibility between branches, uniformly distribute internal forces, realize effective dynamic adjustment, adapt to over-constrained structures with different branch layouts or configurations, and has strong versatility.

[0025] In summary, the application can accurately calculate the internal force of the statically indeterminate branch and realize universal and efficient feedback control, and can be widely applied to high-precision force control scenes such as spacecraft docking devices and precision assembly robots. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The flowchart of embodiment 1 of the application;

[0027] Figure 2 The structural diagram of the over-constrained six-dimensional force sensor before the constraints are disconnected in embodiment 1 of the application;

[0028] Figure 3 The schematic diagram of the over-constrained six-dimensional force sensor after the redundant constraints are disconnected in embodiment 1 of the application;

[0029] Figure 4 The basic system force diagram of the over-constrained six-dimensional force sensor after the disconnected constraints are replaced by unit forces in embodiment 1 of the application;

[0030] Figure 5 The structural schematic diagram of embodiment 2 of the application;

[0031] Figure 6 The structural schematic diagram of the over-constrained robot in embodiment 2 of the application;

[0032] Figure 7 The structural schematic diagram of the UPS branch chain in embodiment 2 of the application;

[0033] Figure 8 The structural schematic diagram of the variable stiffness branch chain in embodiment 2 of the application;

[0034] Figure 9A cross-sectional structure schematic diagram for mounting the telescopic rod and the connecting pipe of the embodiment 2 of the present application;

[0035] Figure 10 A structure schematic diagram of the variable stiffness joint of the embodiment 2 of the present application;

[0036] Figure 11 A structure schematic diagram of the variable stiffness shaft and the main-passive variable stiffness module connection of the embodiment 2 of the present application.

[0037] In the figure: 1, over-constrained robot; 2, hole type part; 3, shaft type part; 4, over-constrained six-dimensional force sensor; 41, S type tension and compression force sensor; 5, upper platform; 6, middle platform; 7, lower platform; 8, UPS branch chain; 81, spherical pair; 82, electric push rod; 9, variable stiffness branch chain; 91, connecting piece; 92, telescopic rod; 93, spring; 94, connecting pipe; 95, variable stiffness joint; 951, load bearing module; 952, variable stiffness shaft; 953, first connecting shaft; 954, second connecting shaft; 955, main-passive variable stiffness module; 10, hooke joint. DETAILED DESCRIPTION

[0038] The present application will be further described in detail through specific embodiments. It should be understood that the described embodiments are only for explaining the present application and do not limit the present application.

[0039] Embodiment 1: A control method of an over-constrained robot based on six-dimensional force feedback solution branch force control

[0040] This embodiment introduces each step in detail according to the flowchart as shown in Figure 1

[0041] S1, build an assembly system containing an over-constrained six-dimensional force sensor, a shaft type part, an over-constrained robot and a hole type part, in the assembly system, the shaft type part is assembled at the end of the over-constrained six-dimensional force sensor, and the hole type part is assembled at the end of the over-constrained robot, forming a shaft hole assembly system.

[0042] S2, establish the mapping relationship between the generalized external force of the over-constrained six-dimensional force sensor and its branch force;

[0043] Based on the displacement coordination equation and the static equilibrium equation, a mathematical mapping model between each branch force of the over-constrained six-dimensional force sensor and the generalized external force acting on it is constructed, the mathematical mapping model is uniquely determined by the structure parameters of the S type tension and compression force sensor in the over-constrained six-dimensional force sensor, the branch force vector can be directly converted into the generalized external force at the center of the shaft part, and the quantitative mapping relationship formula between the two is obtained, the following is the detailed solution process of the mapping relationship between the branch force and the external force of the over-constrained six-dimensional force sensor.

[0044] ​Static equilibrium equations: For an over-constrained six-dimensional force sensor, assume it has n (n>6) branches, and the force of each branch is... According to the equilibrium condition of forces, in the Cartesian coordinate system, the resultant force in all directions is zero, and the resultant torque in all directions is zero.

[0045] Figure 2 For the displacement compatibility equation, in this embodiment n is 10. The over-constrained six-dimensional force sensor has ten branches. The four redundant branch constraints in the over-constrained six-dimensional force sensor structure are removed and replaced with unknown forces, resulting in the following... Figure 3 The basic system shown is in Figure 3 In the basic system, after disconnecting the four redundant constraint branches, six undisconnected branches remain. The undisconnected branches are defined as statically determinate branches, and the remaining four branches are statically indeterminate branches. Then, the following mathematical model can be listed to satisfy the displacement compatibility equation and the static equilibrium equation (the left side is the displacement compatibility equation, and the right side is the matrix expansion of the displacement compatibility equation):

[0046] ;

[0047] in, =[ [This refers to an S-shaped tension / compression sensor in a six-dimensional force sensor under generalized external force.] Internal forces in the unbroken statically indeterminate group branches; is the compliance coefficient matrix of the statically indeterminate group, which represents the displacement and deformation in the direction of force of each branch when the force with a value of 1 after replacing the residual constraint in the statically indeterminate group acts on the basic system alone. This equation describes the deformation of branches 1 to n-6 in the direction of force when the structure of the S-shaped tension / compression sensor in an over-constrained six-dimensional force sensor is subjected to external force only after the over-constrained branches are disconnected. The physical meaning of this equation represents the deformation of the basic system under external force. With the unknown force Under the combined action, the relative displacement between the two ports of the i-th branch with the disconnected constraint is zero. For a matrix, It is an element within the matrix, that is , where i is the number of each branch.

[0048] like Figure 4 As shown, the basic system of the over-constrained six-dimensional force sensor is subjected to external force, and the force state after replacing the redundant constraints with unit force is shown. That is, in this embodiment, the force state of the basic system after the four redundant branch constraints in the over-constrained six-dimensional force sensor are disconnected. This represents the generalized external force experienced by the S-shaped tension / compression sensor in a constrained six-dimensional force sensor. exist Figure 4represents the unit force of the i-th branch of the superstatic component after the broken i-th branch of the redundant constraint is replaced. Figure 4 represents the force state of the basic system after the redundant constraint is replaced by the unit force when the basic system is subjected to the external force.

[0049] .

[0050] According to the Mohr integral theorem, the matrix elements are:

[0051] represents the deformation of the basic system in the axial direction of the i-th branch when the basic system is subjected to the unit force of the j-th branch after the j-th branch is broken. represents the deformation of the basic system in the axial direction of the i-th branch when the basic system is subjected to the j-th branch force. represents the deformation of the basic system in the axial direction of the i-th branch when the basic system is subjected to the original generalized external force.

[0052] When the basic system is subjected to different unit forces that replace the redundant constraints, the internal forces of the other branches are uniformly represented as , is an n-row n-6-column matrix composed of branch forces (n is the total number of branch forces, and n-6 is the total number of redundant constraints of the spatial structure), wherein the elements in the matrix are represents the internal force of the k-th branch when the i-th unit redundant force acts, the upper subscript i indicates that the basic system is subjected to the unit force that replaces the i-th branch redundant constraint at this time (i=1, 2, …, n-6), and the lower subscript k indicates the internal force of the k-th branch (k=1, 2, …, n).

[0053] .

[0054] When the basic system is subjected to the original generalized external force, the internal forces of the other branches are uniformly represented as , is an n-row 1-column matrix composed of branch forces, and for the elements in the matrix , the upper subscript n-5 indicates that the basic system is subjected to the original generalized external force at this time , and the lower subscript k indicates the internal force of the k-th branch.

[0055] .

[0056] The internal forces of the branches and are combined into an n-row n-5-column matrix, and are represented using , wherein and The internal forces of different branches in the six-dimensional force sensor structure under different force conditions are analyzed by using force method.

[0057] .

[0058] The branch forces in the matrix in the above formula can be expressed as follows according to the basic system under different force conditions and different branch groups (hyperstatic group branches and statically determinate group branches) :

[0059] .

[0060] When k = i and n-6, represents the unit force of the kth branch received by the basic system, so it is equal to 1; when the basic system is subjected to a unit force of a certain branch, the branches of the S-type tension and compression force sensor in the over-constrained six-dimensional force sensor can be divided into hyperstatic group branches and statically determinate group branches, for the other hyperstatic group branches except the kth branch, because they are already in the disconnected state, so they are 0, and the other six statically determinate group branches are , is the matrix composed of the influence coefficients of the remaining statically determinate group on the influence coefficients after removing the influence coefficients of the hyperstatic group branches from the original first-order static force influence coefficient matrix G of the S-type tension and compression force sensor in the over-constrained six-dimensional force sensor, is the influence coefficient corresponding to the kth branch subjected to a unit force, because k = i at this time, so the subscript i is used to represent it; when the basic system is subjected to the original generalized external force, the branches of the over-constrained six-dimensional force sensor are also divided into hyperstatic group branches and statically determinate group branches, for the hyperstatic group branches, because they are already in the disconnected state, so they are 0, and the six statically determinate group branches are , is the matrix composed of the influence coefficients of the remaining statically determinate group on the influence coefficients after removing the influence coefficients of the hyperstatic group branches from the original first-order static force influence coefficient matrix G of the S-type tension and compression force sensor in the over-constrained six-dimensional force sensor, is the original generalized external force received by the S-type tension and compression force sensor in the over-constrained six-dimensional force sensor.

[0061] f k The specific expression is as follows:

[0062] .

[0063] According to the superposition principle, the expression of the statically determinate group branches can be obtained:

[0064] .

[0065] The above formula is rearranged as follows:

[0066] .

[0067] The hyperstatic component branch force and the static component branch force are:

[0068] ;

[0069] The two are represented as :

[0070] ;

[0071] The formula is rearranged again:

[0072] ;

[0073] The above formula is combined with the displacement coordination equation to obtain:

[0074] ;

[0075] ;

[0076] .

[0077] wherein, from the expression of the axial stiffness, the axial stiffness expression of one branch is In order to facilitate representation, the axial stiffness of each branch of the hyperstatic group and the axial stiffness of the branch of the static group are respectively composed into stiffness matrices and Both are diagonal matrices composed of the axial stiffness of each branch, and the corresponding matrices of the hyperstatic group branch and the static group branch are specifically represented as follows, and the two are combined.

[0078] .

[0079] and can be represented as:

[0080] ;

[0081] ;

[0082] The above formula is substituted to obtain:

[0083] .

[0084] When the generalized inverse matrix exists, the measurement model expression of the over-constrained parallel six-dimensional force sensor under the condition of stiffness anisotropy of each branch is:

[0085] ;

[0086] .

[0087] This is the mapping relationship between the branch force and the generalized external force of the over-constrained parallel six-dimensional force sensor under the condition of the anisotropy of the stiffness of each branch, wherein, is the generalized external force of the over-constrained six-dimensional force sensor, is the branch force on each branch of the over-constrained six-dimensional force sensor, is the influence matrix calculated.

[0088] S3, the branch force signal of the over-constrained six-dimensional force sensor is collected in real time, and the generalized external force of the shaft part at the end of the over-constrained six-dimensional force sensor is solved through the mapping model of S3.

[0089] S4, the solved generalized external force of the shaft part is transmitted to the hole part through action and reaction, and then transmitted to the end of the over-constrained robot by the hole part.

[0090] S5, the mapping relationship between the force of the over-constrained robot end and the branch driving force thereof is established, which is the same as the mapping relationship between the six-dimensional force sensor and the branch force thereof, that is, , wherein, is the branch driving force of each branch of the over-constrained robot, is the generalized external force of the over-constrained robot, is the influence matrix calculated, and the detailed solving process of the mapping relationship is not described again.

[0091] S6, the branch driving force of the over-constrained robot is solved through the mapping model of S5 with the generalized external force of the over-constrained robot as the input parameter.

[0092] S7, according to the solved branch driving force of the over-constrained robot, the over-constrained robot is controlled to complete the shaft-hole assembly, the balance of force and the position accuracy in the assembly process are ensured through real-time adjustment of each branch force, and precise assembly is realized.

[0093] Embodiment 2: A shaft-hole assembly system based on six-dimensional force feedback for solving branch force

[0094] As shown in Figure 5 , the embodiment includes an over-constrained six-dimensional force sensor 4 for fixing a shaft part 3 and an over-constrained robot 1 for fixing a hole part 2, the over-constrained six-dimensional force sensor 4 drives the shaft part 3 to move, and transmits the force to the hole part 2 through action and reaction, and the over-constrained robot 1 drives the hole part 2 to move according to the force feedback of the hole part 2 by using the control method of embodiment 1.

[0095] The over-constrained six-dimensional force sensor 4 adopts the prior art, which is a mature technology in the field of artificial intelligence robots and will not be described in detail. The over-constrained six-dimensional force sensor 4 with ten branches is adopted in the embodiment. The shaft part 3 is assembled on the over-constrained six-dimensional force sensor 4, and an S-shaped tension and compression force sensor 41 is arranged on each branch of the over-constrained six-dimensional force sensor 4, which is used to obtain the size of the branch force of the over-constrained six-dimensional force sensor 4.

[0096] As shown in Figure 6 , the over-constrained robot 1 comprises an upper platform 5, a middle platform 6 and a lower platform 7, and the hole part 2 is assembled on the upper platform 5. The variable stiffness driving structure is assembled between the upper platform 5 and the middle platform 6 and between the middle platform 6 and the lower platform 7, which is used to receive the force transmitted by the over-constrained six-dimensional force sensor 4 and then acts on the hole part 2 again after calculation. The variable stiffness driving structure comprises four UPS branch chains 8 and a variable stiffness branch chain 9, the variable stiffness branch chain 9 is arranged in the middle of the platform, and the UPS branch chains 8 are uniformly arranged on the circumference of the variable stiffness branch chain 9. Among them, the UPS branch chain 8 is used to receive the generalized external force transmitted by the hole part 2, and after calculation, the branch driving force is obtained, and the UPS branch chain 8 is used to re-act on the hole part 2, and the variable stiffness branch chain 9 is used to make the UPS branch chain 8 move smoothly and ensure the flexibility of the overall movement. As shown in Figure 7 , the UPS branch chain 8 adopts the prior art, which comprises a spherical pair 81, an electric push rod 82 and a hooke joint 10.

[0097] As shown in Figure 8 , the variable stiffness branch chain 9 comprises a connecting piece 91, an extension rod 92, a spring 93, a connecting pipe 94 and a variable stiffness joint 95. The extension rod 92 is fixedly connected with the connecting piece 91. The connecting piece 91 of the embodiment comprises a rectangular plate and four rods. The extension rod 92 is fixed on the rectangular plate, and the four rods are fixedly connected with the upper platform 5 and the middle platform 6. The connecting pipe 94 is fixedly connected with the variable stiffness joint 95. As shown in Figure 9 , the spring 93 is arranged in the connecting pipe 94, and the extension rod 92 is inserted into the connecting rod, and the rod end of the extension rod 92 abuts against one end of the spring 93.

[0098] As shown in Figure 10 , the variable stiffness joint 95 comprises a bearing module 951, a hooke joint 10, a variable stiffness shaft 952 and three master-slave variable stiffness modules 955. The bearing module 951 is in an inverted U-shaped structure and is used to be fixed on the lower platform 7 and the middle platform 6 to play a supporting role. The hooke joint 10 is rotatably arranged on the bearing module 951 through a first connecting shaft 953. Two master-slave variable stiffness modules 955 are connected with the hooke joint 10 through a second connecting shaft 954 and are respectively located on both sides of the second connecting shaft 954. The first connecting shaft 953 and the second connecting shaft 954 are arranged perpendicularly. Figure 11As shown, the variable stiffness shaft 952 is fixed on the hook joint 10, and the third master-slave variable stiffness module 955 is in sliding connection with the variable stiffness shaft 952. The master-slave variable stiffness module 955 adopts the prior art, that is, the structure of the master-slave variable stiffness module in the Chinese invention patent with the publication number CN118876110B and the name of a two-way master-slave variable stiffness joint 95 and a robot based on changing the pre-tightening force of a spring 93, and the action principle has been disclosed in the document and will not be described herein. The assembly direction of the master-slave variable stiffness module 955 on both sides of the second connecting shaft 954 in the present application is opposite to the assembly direction of the master-slave variable stiffness module in the “two-way master-slave variable stiffness joint and robot based on changing the pre-tightening force of a spring”, and the master-slave variable stiffness module 955 in the present application is assembled upward.

[0099] The control method of embodiment 1 is used to assemble the shaft hole structure, which combines mechanical mapping and force-position hybrid control. It starts from the initial position control phase, and the over-constrained robot 1 guides the hole part 2 to approach the shaft part 3 in pure position mode. When the over-constrained six-dimensional force sensor 4 detects that the contact force exceeds the threshold value through the real-time solving branch force mapping relationship, it immediately switches to the force-position hybrid control mode. In this embodiment, the branch force is obtained through the S-shaped tension and compression force sensor 41 on the branch of the over-constrained six-dimensional force sensor 4, and then the branch force is solved to detect the contact force in the shaft hole assembly process. The solving process is the process described in embodiment 1. In the hybrid control phase, the system decouples the task space into a position control loop and a force control loop, and simultaneously transmits the generalized external force solved by the over-constrained six-dimensional force sensor 4 to the external force at the end of the over-constrained robot 1 through Newton's third law. The end external force is real-time solved into each branch driving force through the mapping model of the over-constrained robot 1. These driving force parameters are input into the joint controller to realize accurate output of the actuator on the one hand, and participate in force control loop calculation and dynamic compensation on the other hand.

[0100] The above only describes optional embodiments of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A control method of an over-constrained robot based on six-dimensional force feedback solution branch force control, characterized by, The method comprises the following steps: S1, a six-dimensional force sensor, a shaft part, a constraint robot, and a hole part are assembled to form an assembly system, wherein the shaft part is assembled at the end of the six-dimensional force sensor, and the hole part is assembled at the end of the constraint robot; S2, a mapping relationship between the external force of the six-dimensional force sensor and the branch force thereof is established; S3, the branch force signal of the six-dimensional force sensor is collected in real time, and the external force of the shaft part at the end of the six-dimensional force sensor is calculated; S4, the calculated external force of the shaft part is transmitted to the hole part through action and reaction, and then to the end of the constraint robot; S5, a mapping relationship between the force at the end of the constraint robot and the branch driving force thereof is established; S6, the branch driving force of the constraint robot is calculated by taking the external force of the constraint robot as an input parameter; S7, the constraint robot is controlled according to the calculated branch driving force of the constraint robot to complete the assembly of the shaft and the hole; In S2, the mapping relationship is established based on the displacement coordination equation and the static force balance equation, and satisfies the following mathematical model: ； wherein, is the over-determinate component branch internal force of the S-shaped tensile and compressive force sensor in the over-constrained six-dimensional force sensor under the general external force F, δ is the over-determinate component branch flexibility coefficient matrix, Δ is the deformation of the No. 1 branch to the No. n-6 branch in the stress direction when the over-constrained branch of the S-shaped tensile and compressive force sensor in the over-constrained six-dimensional force sensor is only subjected to the external force after being disconnected. The mapping relationship is: wherein, is a generalized external force suffered by the over-constrained six-dimensional force sensor, is a branch force on each branch of the over-constrained six-dimensional force sensor, and G is an influence matrix between the generalized external force suffered by the over-constrained six-dimensional force sensor and the branch force thereof. In S5, the mapping relationship between the force on the end of the over-constrained robot and the driving force of its branch is: wherein, is the driving force of each branch of the over-constrained robot, is the generalized external force on the over-constrained robot, is the influence matrix between the generalized external force on the over-constrained robot and the driving force of its branch.

2. A shaft-hole assembly system based on six-dimensional force feedback to solve the branch force, characterized in that, The six-dimensional force sensor is used for fixing the shaft part, and the constraint robot is used for fixing the hole part, the six-dimensional force sensor drives the shaft part to move, and transmits the force to the hole part through action and reaction, the constraint robot drives the hole part to move according to the force feedback of the hole part by using the control method for controlling the constraint robot based on the six-dimensional force feedback for calculating the branch force according to claim 1; The constraint robot comprises an upper platform, a middle platform, and a lower platform, the hole part is assembled on the upper platform, variable stiffness driving structures are assembled between the upper platform and the middle platform and between the middle platform and the lower platform, the variable stiffness driving structures comprise at least three UPS branch chains and a variable stiffness branch chain, the variable stiffness branch chain is arranged in the middle, and the UPS branch chains are uniformly arranged on the circumference of the variable stiffness branch chain, wherein the UPS branch chains are used for receiving the external force of the hole part, the branch driving force is obtained after calculation, and the branch driving force is re-applied to the hole part through the UPS branch chains, and the variable stiffness branch chain is used for making the UPS branch chains move smoothly; The variable stiffness joint comprises a bearing module, a hooke joint, a variable stiffness shaft, and three master-slave variable stiffness modules, the hooke joint is rotationally arranged on the bearing module through a first connecting shaft, two master-slave variable stiffness modules are connected with the hooke joint through a second connecting shaft, the first connecting shaft and the second connecting shaft are arranged vertically, the variable stiffness shaft is fixedly arranged on the hooke joint, and the third master-slave variable stiffness module is connected with the variable stiffness shaft. ​

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