Stiffness control algorithm and system of variable stiffness rope-driven anthropomorphic manipulator

Abstract

The present invention provides a stiffness control algorithm and system for a variable-stiffness rope-driven anthropomorphic manipulator, relating to the field of rope-driven anthropomorphic manipulators. The algorithm includes determining the relationship between the change in drive rope length and the forearm rotation angle; establishing a drive rope stiffness-drive rope length change relationship between the stiffness of a variable stiffness module and the drive rope stiffness and drive rope length change; and determining the overall stiffness of the elbow assembly based on the drive rope stiffness-drive rope length change relationship, the relationship between the drive rope length change and the forearm rotation angle, and the current drive rope length change. The present invention proposes a stiffness modeling method for a rope-driven anthropomorphic manipulator with a variable-stiffness elbow assembly, deriving and determining the stiffness of the elbow assembly. Adjusting the drive rope length can change the stiffness of the elbow assembly, and the manipulator arm stiffness can be actively adjusted to an appropriate stiffness based on different mission scenarios, making it suitable for a wider range of application scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of rope-driven humanoid manipulators, and in particular to a stiffness control algorithm and system for a variable-stiffness rope-driven humanoid manipulator. Background Art

[0002] With the rapid development of robotics, rope-driven manipulators have been widely used in various fields due to their lightweight, highly flexible, and agile motion. Compared to traditional rigid manipulators, rope-driven manipulators offer greater safety in human interaction scenarios, as they generate less impact force upon contact.

[0003] In practical applications, if the stiffness of a rope-driven manipulator is too high, it could cause unpredictable harm to the operator in the event of an unexpected situation. On the other hand, if the stiffness of a rope-driven manipulator is too low, its low stiffness could also become a factor limiting its application in certain scenarios requiring precise control and protection, such as medical assistance and space exploration.

[0004] At present, researchers have conducted preliminary explorations into the stiffness of rope-driven manipulators. For example, Professor Kim and Yong Jae's team in South Korea have conducted in-depth research on the structure and control of 7-DOF rope-driven manipulators (Reference: Kim Y J. Anthropomorphic Low-Inertia High-Stiffness Manipulator for High-Speed ​​Safe Interaction [J]. IEEE Transactions on Robotics, 2017, PP(6):1-17.). Many researchers in China have also conducted extensive research on the structure and control of similar 7-DOF rope-driven manipulators. However, no researchers have yet conducted relevant research on variable-stiffness rope-driven manipulators, and there is also a research gap in the variable-stiffness control algorithm for variable-stiffness rope-driven manipulators. Summary of the Invention

[0005] To solve the above problems, an embodiment of the present invention provides a stiffness control algorithm for a variable-stiffness rope-driven anthropomorphic manipulator, wherein the rope-driven anthropomorphic manipulator includes a shoulder assembly, an elbow assembly, and a wrist assembly, wherein the elbow assembly includes a drive assembly for driving a forearm to rotate relative to a large arm, and the drive assembly includes a drive rope provided with a variable stiffness module; the algorithm includes: determining the relationship between the change in the length of the drive rope and the rotation angle of the forearm; establishing a drive rope stiffness-drive rope length change relationship between the stiffness of the variable stiffness module and the stiffness of the drive rope and the change in the length of the drive rope; determining the overall stiffness of the elbow assembly based on the drive rope stiffness-drive rope length change relationship, the relationship between the drive rope length change and the forearm rotation angle, and the current drive rope length change; and determining the stiffness of the rope-driven anthropomorphic manipulator based on the stiffness of the shoulder assembly, the overall stiffness of the elbow assembly, and the stiffness of the wrist assembly.

[0006] The stiffness control algorithm for a variable-stiffness rope-driven anthropomorphic manipulator provided in an embodiment of the present invention proposes a stiffness modeling method for a rope-driven anthropomorphic manipulator with a variable-stiffness elbow component, and derives and determines the stiffness of the elbow component. The stiffness of the elbow component is affected by the change in the length of the drive rope. The stiffness of the elbow component can be changed by adjusting the length of the drive rope, thereby actively adjusting the stiffness of the manipulator arm to an appropriate stiffness according to different mission scenarios, making it suitable for a wider range of application scenarios.

[0007] Optionally, the algorithm further includes: establishing a load-drive rope stiffness relationship between the load and the drive rope stiffness and the drive rope length change; and determining a load-drive rope length change relationship by combining the drive rope stiffness-drive rope length change relationship and the load-drive rope stiffness relationship.

[0008] The embodiment of the present invention establishes a relationship between the load and the stiffness of the drive rope and the change in the length of the drive rope. In order for the robotic arm to maintain a balanced state when picking up a certain load, the relationship between the load and the change in the length of the drive rope must be satisfied. The change in the length of the drive rope can be adjusted to obtain appropriate stiffness, making the robotic arm suitable for the current application scenario.

[0009] Optionally, the variable stiffness module includes four connecting rods, which are rotatably connected in pairs to form a quadrilateral structure, a spring is connected between two opposite vertices of the quadrilateral structure, and the other two vertices are connected to a driving rope; the driving rope includes rope 1 and rope 2;

[0010] The relationship between the driving rope stiffness and the driving rope length change is as follows:

[0011]

[0012] Among them, R is the length of the connecting rod, x is the distance between the other two vertices, K is the elastic coefficient of the spring, k1 is the stiffness of rope 1, k2 is the stiffness of rope 2, Δl1 is the change in rope length of rope 1 caused by the deformation of the variable stiffness module, and Δl2 is the change in rope length of rope 2 caused by the deformation of the variable stiffness module.

[0013] The embodiment of the present invention provides an expression for the relationship between the driving rope stiffness and the driving rope length variation. The driving rope stiffness includes the influence of the variable stiffness module on the rope stiffness. The rope stiffness can be obtained by solving for different rope length variations.

[0014] Optionally, the rope 1 and the rope 2 are both wound around the rotating disk of the forearm and the rotating disk of the upper arm; the overall stiffness of the elbow assembly is as follows:

[0015]

[0016] Where r is the radius of the rotating disk, K e is the overall stiffness of the elbow joint.

[0017] The embodiment of the present invention provides an expression for the overall stiffness of the elbow assembly, based on which the stiffness of the elbow of the drive rope in the current state can be determined.

[0018] Optionally, establishing a load-rope stiffness relationship between the load, the drive rope stiffness, and the change in drive rope length includes:

[0019] The Lagrangian mechanical equilibrium equation for the elbow joint at any position within the rotation range is:

[0020]

[0021] Among them, T i is the pulling force of the driving rope on the arm rotating disk, r i is the instantaneous force arm of the driving rope tension, F is the mechanical arm's own gravity G and the load F s The resultant force, r F is the instantaneous moment arm of the resultant force F;

[0022] F=F S +G

[0023] The following mechanical equilibrium equation is obtained:

[0024]

[0025] Where α is the rotation angle of the line connecting the centers of the two rotating disks, and R(θ) is the moment arm of the resultant force F;

[0026] R(θ)=a1·sin(|90°-θ|)

[0027] Wherein, θ is the rotation angle of the end of the forearm, and a1 is the length from the top of the forearm to the center of mass of the forearm under load.

[0028] The embodiment of the present invention provides an expression for the relationship between the load and the drive rope stiffness and the change in drive rope length, which can be used to adjust the change in drive rope length to obtain appropriate stiffness, making the robotic arm suitable for the current application scenario.

[0029] Optionally, the relationship between the rope length change ΔL1 of the rope 1 and the elbow joint position is as follows:

[0030]

[0031] Wherein, θ is the rotation angle of the end of the small arm, and r is the radius of the rotating disk;

[0032] The relationship between the rope length change ΔL1 of the rope 2 and the elbow joint position is as follows:

[0033]

[0034] The embodiment of the present invention provides an expression for the relationship between the change in the length of the driving rope and the position of the elbow joint, and obtains the relationship between the rotation angle of the elbow joint and the change in the rope length.

[0035] Optionally, the derivation process of the overall stiffness of the elbow assembly is as follows:

[0036] When the elbow joint is in equilibrium, a small input torque ΔT is applied to the end of the joint. The output end of the forearm will produce a very small rotation angle Δθ. The expansion and contraction of ropes 1 and 2 is ΔL. According to the principle of virtual work, we can get:

[0037] ΔT·Δθ=T2·ΔL-T1·ΔL

[0038] Among them, T2 and T1 are the tensions exerted by rope 2 and rope 1 on the arm rotating disk; after sorting, we can get:

[0039]

[0040] Where J is the Jacobian matrix from elbow joint angular velocity to rope velocity, θ is the rotation angle of the end of the small arm, and r is the radius of the rotating disk;

[0041] The spring deforms, causing the tension to change. The above formula can be written as:

[0042]

[0043] Among them, T g It is the tension of the rope when the elbow joint is not subject to any external force;

[0044] The rope stiffness can be expressed as:

[0045]

[0046] available:

[0047]

[0048] The change in rope length due to the deformation of the spring is the same as the change in rope length in the joint as a whole, that is:

[0049]

[0050] Therefore, the overall stiffness of the elbow component is obtained:

[0051]

[0052] Optionally, the stiffness of the rope-driven anthropomorphic manipulator is as follows:

[0053] K=J(q) +T (K θ +K t )J(q) +

[0054] Where: J(q) + is the generalized inverse matrix of the Jacobian matrix J(q); K θ K is the stiffness corresponding to each joint; t is the compensation stiffness matrix.

[0055] The embodiment of the present invention provides an expression for the overall stiffness of a rope-driven anthropomorphic manipulator. Based on the determination of the variable stiffness of the elbow assembly, the overall stiffness of the manipulator can be further determined.

[0056] An embodiment of the present invention provides a stiffness control system for a variable-stiffness rope-driven anthropomorphic manipulator arm. The rope-driven anthropomorphic manipulator arm includes a shoulder assembly, an elbow assembly, and a wrist assembly. The elbow assembly includes a drive assembly for driving a forearm to rotate relative to a forearm, and the drive assembly includes a drive rope provided with a variable stiffness module. The system includes: a rope length change and angle relationship determination module for determining a relationship between a drive rope length change and a forearm rotation angle; a rope stiffness and length change relationship determination module for establishing a drive rope stiffness-drive rope length change relationship between the stiffness of the variable stiffness module and the drive rope stiffness and the drive rope length change; an elbow stiffness determination module for determining the overall stiffness of the elbow assembly based on the drive rope stiffness-drive rope length change relationship, the relationship between the drive rope length change and the forearm rotation angle, and the current drive rope length change; and a manipulator arm stiffness determination module for determining the stiffness of the rope-driven anthropomorphic manipulator arm based on the shoulder assembly stiffness, the overall stiffness of the elbow assembly, and the wrist assembly stiffness.

[0057] Optionally, the system further includes a load and length change relationship determination module, which is used to: establish a load-drive rope stiffness relationship between the load and the drive rope stiffness and the drive rope length change; and determine a load-drive rope length change relationship based on the drive rope stiffness-drive rope length change relationship and the load-drive rope stiffness relationship.

[0058] The stiffness control system of the variable stiffness rope-driven anthropomorphic manipulator provided by the embodiment of the present invention can achieve the same technical effect as the stiffness control algorithm of the variable stiffness rope-driven anthropomorphic manipulator described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0060] Figure 1 A schematic flow chart of a stiffness control algorithm for a variable stiffness rope-driven anthropomorphic manipulator provided in an embodiment of the present invention;

[0061] Figure 2 A schematic diagram illustrating the effect of a change in the length of a drive rope on the position of an elbow joint in an elbow assembly provided by an embodiment of the present invention;

[0062] Figure 3 An exemplary structural diagram of the stiffness of a variable stiffness module provided in an embodiment of the present invention;

[0063] Figure 4 A schematic diagram of the forces acting on the elbow assembly provided by an embodiment of the present invention;

[0064] Figure 5 Schematic diagram of the lever arm of the forearm in the no-load state and the loaded state provided by the embodiment of the present invention;

[0065] Figure 6 This is a schematic structural diagram of a stiffness control system for a variable stiffness rope-driven anthropomorphic manipulator provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0066] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0067] Today, rope-driven manipulators are highly sought after by researchers for their light weight, low inertia, and high speed. Their lower stiffness and greater compliance compared to traditional rigid manipulators are also key advantages, making them valuable for applications requiring safe interaction. However, in practical applications, excessive stiffness can cause unpredictable harm to operators, while insufficient stiffness can hinder their use in scenarios requiring precise control and protection.

[0068] This embodiment of the present invention provides a rope-driven anthropomorphic manipulator with a variable-stiffness structure at the elbow, enabling active stiffness adjustment. This makes it suitable for a wider range of applications, allowing for appropriate stiffness adjustment based on different mission scenarios. For this rope-driven anthropomorphic manipulator, this embodiment of the present invention establishes a stiffness control algorithm model.

[0069] The embodiments of the present invention provide an algorithm model for stiffness control of a rope-driven anthropomorphic manipulator with variable stiffness. The aim is to actively adjust the stiffness of the manipulator to make it applicable to a wider range of application scenarios and provide safer and more reliable services in human-computer interaction.

[0070] Exemplarily, the rope-driven anthropomorphic manipulator includes a shoulder assembly, an elbow assembly, and a wrist assembly. The shoulder assembly is connected to the wrist assembly via the elbow assembly. The elbow assembly includes a pivotally connected upper arm and lower arm, and a drive assembly that drives the lower arm to rotate relative to the upper arm. The shoulder assembly is connected to the upper arm, and the wrist assembly is pivotally connected to the lower arm. The drive assembly includes a drive rope equipped with a variable stiffness module. The drive rope is in transmission connection with the upper arm, lower arm, and wrist assembly.

[0071] The ends of the drive rope are fixed and wound around two power shafts (driven by motors) and around the rotating disks of the lower arm and the upper arm. When the power shafts rotate, the drive rope drives the two rotating disks. A variable stiffness module can be connected in the middle of the drive rope, and its deformation can adjust the stiffness of the drive rope.

[0072] Figure 1 This is a flow chart of a stiffness control algorithm for a variable stiffness rope-driven anthropomorphic manipulator provided in an embodiment of the present invention. The algorithm includes:

[0073] S102, determining the relationship between the change in the length of the driving rope and the rotation angle of the forearm.

[0074] Taking the elbow joint control of the robotic arm as an example, the drive rope is driven by the power shaft, which can drive the rotating disk in the robotic arm to rotate, thereby driving the forearm to rotate.

[0075] As the arm moves from its original position to its target position, the length of the drive rope changes accordingly. The relationship between the arm's rotation angle and the change in drive rope length can be determined through geometric relationships.

[0076] S104: establishing a driving rope stiffness-driving rope length variation relationship between the stiffness of the variable stiffness module and the driving rope stiffness and driving rope length variation.

[0077] A variable stiffness module is connected to the middle of the drive rope. Adjusting the length of the drive rope can change the stiffness of the module. Assuming the drive rope is rigid, changes in the drive rope length cause deformation of the variable stiffness module, thereby changing the overall stiffness of the drive rope. A relationship can be established between the stiffness of the variable stiffness module, the stiffness of the drive rope, and the change in the drive rope length. In other words, given the stiffness of the variable stiffness module and the change in the drive rope length, the drive rope stiffness can be calculated.

[0078] For example, a spring may be provided in the variable stiffness module, and the spring is combined with an auxiliary component to realize the nonlinearity of the variable stiffness module.

[0079] S106 , determining the overall stiffness of the elbow assembly based on the relationship between the driving rope stiffness and the driving rope length change, the relationship between the driving rope length change and the forearm rotation angle, and the current driving rope length change.

[0080] After determining the aforementioned relationship between drive rope stiffness and drive rope length change, and combining it with the relationship between drive rope length change and arm rotation angle, the overall elbow assembly stiffness can be derived for very small arm rotation angles. This overall elbow assembly stiffness is expressed based on the current drive rope length change. Adjusting the current drive rope length change can alter the overall elbow assembly stiffness, thereby actively adjusting the stiffness of the robotic arm, making it suitable for a wider range of application scenarios.

[0081] Based on the above expression of the overall stiffness of the elbow assembly and the change in the length of the drive rope, the stiffness of the elbow joint can be changed by adjusting the length of the drive rope, thereby realizing variable stiffness control of the robotic arm.

[0082] S108 , determining the stiffness of the rope-driven anthropomorphic manipulator according to the stiffness of the shoulder assembly, the overall stiffness of the elbow assembly, and the stiffness of the wrist assembly.

[0083] After determining the overall stiffness of the elbow assembly, the stiffness of the rope-driven anthropomorphic manipulator can be calculated by combining the stiffness of the shoulder and wrist assemblies. By adjusting the stiffness of the elbow joint, the overall stiffness of the manipulator can be adjusted. For example, a serial manipulator stiffness model can be used.

[0084] The stiffness control algorithm for a variable-stiffness rope-driven anthropomorphic manipulator provided in an embodiment of the present invention proposes a stiffness modeling method for a rope-driven anthropomorphic manipulator with a variable-stiffness elbow assembly, and derives and determines the overall stiffness of the elbow assembly. The overall stiffness of the elbow assembly is affected by the change in the length of the drive rope. The stiffness of the elbow assembly can be changed by adjusting the length of the drive rope, so that the stiffness of the manipulator arm can be actively adjusted to an appropriate stiffness according to different mission scenarios, making it suitable for a wider range of application scenarios.

[0085] Since a robotic arm typically has a load at its end during use, this embodiment also establishes a relationship between the load, the stiffness of the drive rope, and the change in the length of the drive rope. For the robotic arm to maintain balance while lifting a load, this relationship must be met.

[0086] Based on this, the above algorithm includes: establishing a load-drive rope stiffness relationship between the load and the drive rope stiffness and the change in drive rope length; and, combining the above drive rope stiffness-drive rope length change relationship and the load-drive rope stiffness relationship, determining the load-drive rope length change relationship.

[0087] Considering the derived relationship between drive rope stiffness and drive rope length variation, combined with the aforementioned load-drive rope stiffness relationship, we can derive the relationship between load and drive rope length variation. Therefore, for the robot arm in this embodiment to maintain balance while lifting a load, this load-drive rope length variation relationship must be satisfied.

[0088] For a certain load, there can be multiple drive rope length changes that satisfy the above relationship and can all keep the robot arm balanced. However, different drive rope length changes correspond to different elbow joint stiffnesses. The drive rope length changes can be adjusted to obtain appropriate stiffness to make the robot arm suitable for the current application scenario.

[0089] Figure 2 A schematic diagram showing the effect of changes in the drive rope length in the elbow assembly on the elbow joint position. Figure 2 The figure shows the rotating disks of the upper and lower arms of the elbow assembly. The drive ropes include rope 1 (thick solid line) and rope 2 (thick dashed line), both of which are wrapped around the rotating disks of the lower and upper arms. The length changes of rope 1 and rope 2 drive the rotating disks. The drive ropes are rigid by default.

[0090] like Figure 2 As shown in the figure, after the arm of the robot moves from the original position M to the target position N, the geometric relationship shows that β = α. Since the radii of the two rotating disks are equal, it can be seen that the rotation angle θ at the end of the arm is twice the rotation angle α of the rotating disk (planetary gear structure), that is:

[0091] θ=2α (1.1)

[0092] Rope length variation:

[0093] ΔL=2×δL (1.2)

[0094] δL=βπr / 180° (1.3)

[0095] Where r is the radius of the elbow rotating disk, δL is the arc length corresponding to the angle θ;

[0096] therefore:

[0097] The relationship between the movement angle of the robotic arm's elbow joint and the change in the length of the two ropes is obtained as follows:

[0098] Elongation of rope 1:

[0099]

[0100] Elongation of rope 2:

[0101]

[0102] The relationship between the speed of the rope and the angular velocity of the elbow joint is derived as follows:

[0103] because:

[0104] in, is the speed of the rope, is the joint angular velocity, J is arrive The Jacobian matrix of ;

[0105] Combined with (1.4), we can know that:

[0106]

[0107] Figure 3 FIG. 1 shows an exemplary structural diagram of the stiffness of the variable stiffness module provided by an embodiment of the present invention. Figure 3 The medium variable stiffness module takes a quadrilateral structure including a spring as an example. Specifically, the variable stiffness module includes four connecting rods, which are connected in pairs to form a quadrilateral structure. A spring is connected between two opposite vertices of the quadrilateral structure, and the other two vertices are connected to a drive rope.

[0108] The above quadrilateral structure is deformed by the tension of the drive ropes on both sides. The stiffness K(X) of the drive rope including the influence of the quadrilateral structure is expressed as follows:

[0109]

[0110] Where X0 is the initial length of the quadrilateral structure, that is, the distance between the left and right vertices, X is the length of the quadrilateral structure after being subjected to force, F is the tensile force on the quadrilateral structure, R is the length of the connecting rod, and K is the elastic coefficient of the spring;

[0111] Taking rope 1 and rope 2 as examples, the relationship between the driving rope stiffness and the change in driving rope length, including the influence of the variable stiffness module, is as follows:

[0112]

[0113] Where x is the initial length of the quadrilateral structure, K is the elastic coefficient of the spring, k1 is the stiffness of rope 1, k2 is the stiffness of rope 2, Δl1 is the change in rope length of rope 1 caused by the deformation of the variable stiffness module, and Δl2 is the change in rope length of rope 2 caused by the deformation of the variable stiffness module.

[0114] Based on the above relationship, for different Δl1 and Δl2, the stiffness of rope 1 and the stiffness of rope 2 can be solved.

[0115] Elbow assembly overall stiffness k e The relationship between the stiffness k1 and k2 of the two ropes is derived as follows:

[0116] When the elbow joint is in equilibrium, a small input torque ΔT is applied to the end of the joint. The end of the elbow joint forearm will produce a very small rotation angle Δθ. The amount of expansion and contraction of rope 1 and rope 2 is ΔL. According to the principle of virtual work, we can get:

[0117] ΔT·Δθ=T2·ΔL-T1·ΔL (1.12)

[0118] Among them, T2 and T1 are the tensions exerted by rope 2 and rope 1 on the arm rotating disk, which are also the output tensions of the ropes in the variable stiffness module;

[0119] Arranging (1.12) yields:

[0120]

[0121] Wherein, J is the above arrive The Jacobian matrix of ;

[0122] Since the joint stiffness is variable, when a preload torque ΔT is applied to the joint end, the joint rotates Δθ, and the spring deforms, causing the tension to change. Equation (1.13) can be written as:

[0123]

[0124] Among them, T g It is the tension of the rope when the joint is not subject to any external force;

[0125] The rope stiffness can be expressed as:

[0126]

[0127] Therefore (1.14) can be further organized as:

[0128]

[0129] Where k1 and k2 are the stiffnesses of rope 1 and rope 2, respectively, and Δl1 and Δl2 are the length changes of the ropes due to spring deformation. Since the joint is only subject to external torque, the length change of each rope group due to spring deformation is the same as the length change of each rope group in the joint as a whole, that is:

[0130]

[0131] Therefore, the overall stiffness of the elbow joint K e as follows:

[0132]

[0133] The relationship between load Fs and stiffness k1 and k2 is established below.

[0134] According to the way the rope tension acts on the forearm, the Lagrangian mechanical equilibrium equation for the elbow joint at any position within the rotation range can be derived as follows:

[0135]

[0136] Among them, T i is the tension of the driving rope on the arm rotating disk, which is also the output tension of the rope in the variable stiffness module, r i is the instantaneous force arm of the driving rope tension, F is the mechanical arm's own gravity G and the load F s The resultant force, r F is the instantaneous moment arm of the resultant force F;

[0137] F=F S +G (1.20)

[0138] Figure 4 Figure 2 shows a schematic diagram of the forces acting on the elbow assembly. Figure 4 As shown:

[0139] The resultant force of the two ropes is:

[0140] T=k2Δl2-k1Δl1 (1.21)

[0141] The component of the resultant force of the rope tension on the lever arm is:

[0142]

[0143] The moment arms of the two rope tensions are equal:

[0144]

[0145] Combining (1.19)-(1.23), we can obtain the following mechanical equilibrium equation:

[0146]

[0147] Where α is the rotation angle of the line connecting the centers of the two rotating disks, and R(θ) is the force arm of F, which is also a function of θ. The solution process for R(θ) is as follows:

[0148] The forearm is simplified to a rod of uniform mass. Figure 5 The figure shows the arm diagram of the forearm in the no-load state and the loaded state. Figure 5 As shown, the center of mass of the forearm in the unloaded state divides its length into A1 and A2, and the respective weights are F1 and F2. The center of mass of the forearm in the loaded state divides its length into a1 and a2, and the respective weights are f1 and f2. The following relationship exists:

[0149] F1A1=F2A2

[0150] A1+A2=a1+a2

[0151] f1a1=(f2+F S )a2

[0152]

[0153] f1+f2=F1+F2

[0154] According to the above conditions, the relationship between a1 and R(θ) can be obtained:

[0155] R(θ)=a1·sin(|90°-θ|)

[0156] Formula (1.24) can be written as:

[0157]

[0158] Where θ is the rotation angle of the forearm end, and a1 is the length from the forearm top to the forearm center of mass under load.

[0159] For example, the overall stiffness of the anthropomorphic robotic arm is as follows:

[0160] Serial manipulator stiffness: K = J(q) +T (K θ +K t )J(q) +

[0161] Among them, J(q) + is the generalized inverse matrix of the Jacobian matrix J(q); K θ The stiffness corresponding to each joint is a diagonal matrix; K t is the compensation stiffness matrix, for the stiffness compensation matrix K t Introducing two evaluation indicators, v p With v r and represent the stiffness compensation matrix K t The effect on the end displacement and end angle. By applying joint stiffness values ​​and giving different load forces at the end of the robot, v p With v r The value of K t Impact on the overall stiffness of the robot.

[0162] Taking the 7-DOF rope-driven anthropomorphic arm as an example, the wrist has rotation and pitch degrees of freedom as parallel degrees of freedom, so it cannot be modeled according to the above serial robot arm stiffness model.

[0163] Since the elbow stiffness is independent of the rotation angle and only related to the pitch angle, the stiffness of the 7-DOF anthropomorphic arm is equivalent to the stiffness of 6 DOF (excluding the wrist rotation degree of freedom).

[0164] For the equivalent 6-DOF rope-driven anthropomorphic arm:

[0165]

[0166] The Jacobian matrix of the equivalent 6-DOF manipulator is: J D (q)

[0167] Therefore: K = J D (q) +T (K θ +K t )J D (q) +

[0168] Each joint of the shoulder assembly is directly connected by a cable, so the stiffness of each joint is the stiffness k of the cable. cable , that is: k shoulder_1 =k shoulder_2 =k shoulder_3 =k cable ; Pitch stiffness k of wrist assembly wrist_pitch , flip stiffness k wrist_ro The calculation method in existing literature can be used and will not be described here in detail.

[0169] In summary, the stiffness of the anthropomorphic robotic arm is as follows:

[0170] K NRB =J D (q)+T (K θ +K t )J D (q) + .

[0171] In the embodiments of the present invention, a rope-driven anthropomorphic manipulator with a variable stiffness structure at the elbow allows for active stiffness adjustment, making it applicable to a wider range of applications and enabling appropriate stiffness adjustment based on different mission scenarios. This embodiment establishes a stiffness control algorithm model for this manipulator, deriving an expression for the overall stiffness of the elbow assembly based on the change in drive rope length, as well as a relationship between load, drive rope stiffness, and change in drive rope length. This allows for active stiffness adjustment of the manipulator, ensuring operation with an appropriate overall stiffness. This allows for wider application scenarios and provides safer and more reliable services in human-machine interaction.

[0172] Figure 6 A schematic diagram of the structure of a stiffness control system for a variable-stiffness rope-driven anthropomorphic manipulator provided in an embodiment of the present invention is shown. The rope-driven anthropomorphic manipulator includes a shoulder assembly, an elbow assembly, and a wrist assembly. The elbow assembly includes a drive assembly for driving the forearm to rotate relative to the upper arm. The drive assembly includes a drive rope equipped with a variable stiffness module. The system includes:

[0173] The rope length variation and angle relationship determination module 601 is used to determine the relationship between the driving rope length variation and the arm rotation angle;

[0174] A rope stiffness and length variation relationship determination module 602 is configured to establish a driving rope stiffness-driving rope length variation relationship between the stiffness of the variable stiffness module and the driving rope stiffness and the driving rope length variation;

[0175] an elbow stiffness determination module 603 for determining the overall stiffness of the elbow assembly based on the relationship between the drive rope stiffness and the drive rope length change, the relationship between the drive rope length change and the forearm rotation angle, and the current drive rope length change;

[0176] The manipulator stiffness determination module 604 is configured to determine the stiffness of the rope-driven anthropomorphic manipulator according to the stiffness of the shoulder assembly, the overall stiffness of the elbow assembly, and the stiffness of the wrist assembly.

[0177] As a feasible approach, the system further includes a module for determining the relationship between load and length variation, which is used to:

[0178] Establishing a load-drive rope stiffness relationship among the load, the drive rope stiffness, and the change in the drive rope length;

[0179] The load-drive rope length variation relationship is determined by combining the drive rope stiffness-drive rope length variation relationship and the load-drive rope stiffness relationship.

[0180] The stiffness control system of the variable stiffness rope-driven anthropomorphic manipulator provided by the embodiment of the present invention can achieve the same technical effect as the stiffness control algorithm of the variable stiffness rope-driven anthropomorphic manipulator described above.

[0181] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

[0182] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0183] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the above embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0184] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A stiffness control algorithm for a variable stiffness rope-driven anthropomorphic manipulator, characterized in that: The rope-driven anthropomorphic manipulator includes a shoulder assembly, an elbow assembly, and a wrist assembly. The elbow assembly includes a drive assembly for driving a lower arm to rotate relative to a main arm. The drive assembly includes a drive rope provided with a variable stiffness module. The algorithm includes: Determine the relationship between the change in the length of the drive rope and the rotation angle of the forearm; Establishing a drive rope stiffness-drive rope length variation relationship between the stiffness of the variable stiffness module, the stiffness of the drive rope, and the drive rope length variation; wherein this step includes: connecting the variable stiffness module to the middle of the drive rope, changing the stiffness of the variable stiffness module by adjusting the drive rope length, thereby changing the stiffness of the entire drive rope; establishing a relationship between the stiffness of the variable stiffness module, the drive rope stiffness, and the drive rope length variation; and solving for the drive rope stiffness when the stiffness of the variable stiffness module and the drive rope length variation are known; Determining the overall stiffness of the elbow assembly based on the relationship between the drive rope stiffness and the change in drive rope length, the relationship between the change in drive rope length and the rotation angle of the forearm, and the current change in drive rope length; wherein this step includes: after determining the relationship between the drive rope stiffness and the change in drive rope length, combining the relationship between the change in drive rope length and the rotation angle of the forearm, and deriving the overall stiffness of the elbow assembly based on the principle of virtual work when the forearm rotates at a very small angle; The stiffness of the rope-driven anthropomorphic manipulator is determined according to the stiffness of the shoulder component, the overall stiffness of the elbow component, and the stiffness of the wrist component.

2. The algorithm according to claim 1, characterized in that The algorithm also includes: Establishing a load-drive rope stiffness relationship among the load, the drive rope stiffness, and the change in the drive rope length; The load-drive rope length variation relationship is determined by combining the drive rope stiffness-drive rope length variation relationship and the load-drive rope stiffness relationship.

3. The algorithm according to claim 2, characterized in that The variable stiffness module includes four connecting rods, which are rotatably connected in pairs to form a quadrilateral structure. A spring is connected between two opposite vertices of the quadrilateral structure, and the other two vertices are connected to a drive rope. The drive rope includes rope 1 and rope 2. The relationship between the driving rope stiffness and the driving rope length change is as follows: Wherein, R is the length of the connecting rod, x is the distance between the other two vertices, K is the elastic coefficient of the spring, k1 is the stiffness of rope 1, k2 is the stiffness of rope 2, is the change in rope length of rope 1 caused by the deformation of the variable stiffness module, is the change in rope length of rope 2 caused by the deformation of the variable stiffness module.

4. The algorithm according to claim 3, characterized in that The rope 1 and the rope 2 are both wound around the rotating disk of the forearm and the rotating disk of the upper arm; the overall stiffness of the elbow assembly is as follows: Wherein, r is the radius of the rotating disk, is the overall stiffness of the elbow joint.

5. The algorithm according to claim 3, characterized in that The establishing of the load-rope stiffness relationship between the load and the drive rope stiffness and the change in the length of the drive rope comprises: The Lagrangian mechanical equilibrium equation for the elbow joint at any position within the rotation range is: Among them, T i is the pulling force of the driving rope on the arm rotating disk, r i is the instantaneous force arm of the driving rope tension, F is the mechanical arm's own gravity G and the load F s The combined force, is the instantaneous moment arm of the resultant force F; The following mechanical equilibrium equation is obtained: in, is the rotation angle of the line connecting the centers of the two rotating disks, R(θ) is the moment arm of the resultant force F; Where θ is the rotation angle of the end of the forearm, It is the length from the top of the forearm to the center of mass of the forearm under load.

6. The algorithm according to claim 4, characterized in that The change in the length of the rope 1 The relationship with the elbow joint position is as follows: Wherein, θ is the rotation angle of the end of the small arm, and r is the radius of the rotating disk; The change in the length of the rope 2 The relationship with the elbow joint position is as follows: 。 7. The algorithm according to claim 4, characterized in that The derivation process of the overall stiffness of the elbow assembly is as follows: When the elbow joint is in equilibrium, a small input torque ΔT is applied to the end of the joint. The output end of the forearm will produce a very small rotation angle Δθ. The expansion and contraction of ropes 1 and 2 is ΔL. According to the principle of virtual work, we can get: Among them, T2 and T1 are the tensions exerted by rope 2 and rope 1 on the arm rotating disk; after sorting, we can get: Where J is the Jacobian matrix from elbow joint angular velocity to rope velocity, , θ is the rotation angle of the end of the small arm, r is the radius of the rotating disk; The spring deforms, causing the tension to change. The above formula can be written as: Among them, T g It is the tension of the rope when the elbow joint is not subject to any external force; The rope stiffness can be expressed as: available: The change in rope length due to the deformation of the spring is the same as the change in rope length in the joint as a whole, that is: Therefore, the overall stiffness of the elbow component is obtained: 。 8. The algorithm according to claim 4, characterized in that The stiffness of the rope-driven anthropomorphic manipulator is as follows: in: is the Jacobian matrix The generalized inverse matrix of ; is the stiffness corresponding to each joint; is the compensation stiffness matrix.

9. A stiffness control system for a variable stiffness rope-driven anthropomorphic manipulator, characterized in that: The rope-driven anthropomorphic manipulator includes a shoulder assembly, an elbow assembly, and a wrist assembly. The elbow assembly includes a drive assembly for driving the forearm to rotate relative to the upper arm. The drive assembly includes a drive rope provided with a variable stiffness module. The system includes: A module for determining the relationship between the change in length of the rope and the angle, used to determine the relationship between the change in length of the driving rope and the rotation angle of the forearm; a rope stiffness and length variation relationship determination module, configured to establish a driving rope stiffness-driving rope length variation relationship between the stiffness of the variable stiffness module, the driving rope stiffness, and the driving rope length variation; wherein the variable stiffness module is connected to the middle of the driving rope, and the stiffness of the variable stiffness module is changed by adjusting the driving rope length, thereby changing the stiffness of the entire driving rope; a relationship is established between the stiffness of the variable stiffness module, the driving rope stiffness, and the driving rope length variation; and, given the stiffness of the variable stiffness module and the driving rope length variation, the driving rope stiffness is determined; an elbow stiffness determination module, configured to determine the overall stiffness of the elbow assembly based on the relationship between the drive rope stiffness and the change in drive rope length, the relationship between the change in drive rope length and the arm rotation angle, and the current change in drive rope length; wherein, after determining the relationship between the drive rope stiffness and the change in drive rope length, the overall stiffness of the elbow assembly is derived based on the principle of virtual work when the arm rotates at a very small angle, in combination with the relationship between the change in drive rope length and the arm rotation angle; The robot arm stiffness determination module is used to determine the stiffness of the rope-driven anthropomorphic robot arm according to the stiffness of the shoulder component, the overall stiffness of the elbow component, and the stiffness of the wrist component.

10. The system according to claim 9, characterized in that The system further includes a module for determining a relationship between load and length variation, for: Establishing a load-drive rope stiffness relationship among the load, the drive rope stiffness, and the change in the drive rope length; The load-drive rope length variation relationship is determined by combining the drive rope stiffness-drive rope length variation relationship and the load-drive rope stiffness relationship.

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