Variable-rigidity rope-driven joint and rigidity calculation method thereof

Abstract

The invention belongs to the technical field of rope-driven robots, and particularly relates to a variable-rigidity rope-driven joint and a rigidity calculation method thereof. Comprising a base, a swash plate, a cross hinge and a plurality of geometrically variable pulley blocks, a base tray is arranged on the base and is used for being rotationally connected with the cross hinge; the swash plate is rotationally connected with the cross hinge; the geometric variable pulley block comprises a rope, a swash plate rope hole formed below the swash plate, a first base rope hole and a second base rope hole which are formed in the bottom of the base, a sliding rail fixed between the bottom of the base and the base tray, and a sliding seat and a spring which are arranged on the sliding rail in a sleeving manner; the spring is positioned between the sliding seat and the bottom of the base; a sliding rope hole is formed in the sliding seat; one end of the rope is fixed on the sliding seat and then sequentially penetrates through the first base rope hole, the swash plate rope hole, the sliding rope hole and the second base rope hole, and then the tail end of the rope is connected with the motor and used for adjusting the posture of the swash plate through the rope. The variable-stiffness joint is easy to model, regulate and control and has a large joint stiffness change range.

Description

Technical Field

[0001] The invention belongs to the technical field of rope-driven robots, and in particular relates to a variable-rigidity rope-driven joint and a method for calculating its stiffness. Background Art

[0002] In order to make the serpentine robot have the characteristic of changing stiffness, the joints or connecting rods of the serpentine robot often introduce materials or structures with special controlled stiffness characteristics such as springs, shape memory alloys or particle groups. In the Chinese invention patent CN113386166A, a decoupled variable stiffness joint suitable for a super redundant robot is disclosed. The joint controls the temperature of the liquid metal inside the hollow accordion-type variable stiffness driver body in the joint to make the liquid metal solid, thereby fixing the corresponding control joint and improving the stiffness of the serpentine robot. In the academic conference "201712th IEEE Conference on Industrial Electronics and Applications" held from June 18 to 20, 2017, a 2-DOF rope-driven joint module with variable stiffness was included in the conference. In order to increase the stiffness range, this scheme proposes a variable stiffness device with a compact configuration and optimizes it, and proposes a design optimization method for a 2-DOF rope-driven joint module to obtain a larger adjustable stiffness range.

[0003] In these two variable stiffness joint schemes for snake-like manipulators, the former introduces complex phase-change metal materials and uses temperature control to change the metal phase, thereby changing the stiffness of the joint. This stiffness control method is difficult to model and control, and cannot continuously change the stiffness of the joint; while the latter introduces a variable stiffness joint module based on a spring, which slightly increases the range of joint stiffness variation, but it still has the problem of limited stiffness range. In addition, in these two schemes, the transmission ratio between the drive and the joint remains constant, which means that no matter how much external interference the joint is subjected to, the disturbance will be transmitted to the rope in a uniform proportion, which is not conducive to the anti-disturbance performance of the joint. Summary of the invention

[0004] The object of the present invention is to provide a variable stiffness rope driven joint and a stiffness calculation method thereof, so as to improve the joint stiffness variation range and anti-disturbance performance.

[0005] To achieve the above object, the present invention provides a variable stiffness joint, comprising a base, a swash plate, a cross hinge and a plurality of sets of geometrically variable pulley blocks;

[0006] The base is provided with a base tray for rotationally connecting with the cross hinge; the swash plate is rotationally connected with the cross hinge;

[0007] The variable geometry pulley assembly comprises a rope, a slant plate rope hole arranged below the slant plate, a first base rope hole and a second base rope hole arranged at the bottom of the base, a slide rail fixed between the bottom of the base and the base tray, and a sliding seat and a spring sleeved on the slide rail; the spring is located between the sliding seat and the bottom of the base; the sliding seat is provided with a sliding rope hole;

[0008] One end of the rope is fixed on the sliding seat, and then passes through the first base rope hole, the swash plate rope hole, the sliding rope hole and the second base rope hole in sequence, and the end thereof is connected to the motor for adjusting the position of the swash plate through the rope.

[0009] Furthermore, the rope from the fixed point on the sliding seat to the rope hole of the first base and the rope from the sliding rope hole to the rope hole of the second base are parallel to each other.

[0010] Furthermore, the variable geometry pulley groups are three groups, which are evenly spaced and distributed between the base and the swash plate.

[0011] Furthermore, an upper gear and a lower gear are respectively provided at the top and bottom of the cross hinge, a rotating gear meshing with the upper gear is provided on the swash plate, and a gear meshing with the lower gear is provided at the bottom of the base; angular displacement sensors are respectively provided at the meshing points of the upper gear and the lower gear.

[0012] The present invention also provides a method for determining the stiffness of a variable stiffness joint, comprising: constructing a joint stiffness equation and a joint multi-dimensional state set as shown in (1), then using a particle swarm algorithm in this set, taking the basic structure of the joint as a constraint and minimizing the joint potential energy as a solution target, solving the joint state, and then substituting it into the joint stiffness equation to obtain the joint stiffness:

[0013]

[0014] Among them, K j is the joint stiffness, K S is the stiffness of the spring, K c is the rope stiffness, f is the tension on the driving rope, J l is the Jacobian matrix of the joint pose, J l T is the transpose of the Jacobian matrix, and q is the joint angular displacement.

[0015] Furthermore, the joint potential energy is as shown in formula (2):

[0016]

[0017] Where E is the joint potential energy, K S is the stiffness of the spring, x sis the compression of the spring, K c is the rope stiffness, and l is the elongation of the driving rope.

[0018] Furthermore, the multi-dimensional state set of the joint includes a basic structural parameter set of a geometrically variable pulley set, a DH parameter set and a particle swarm parameter set.

[0019] Furthermore, the basic structural parameter set of the geometrically variable pulley block includes the spatial vector from the first base rope hole (53) to the swash plate rope hole (51) in the geometrically variable pulley block j. The space vector from the first base rope hole (53) to the joint rotation center The space vector from the sliding rope hole (52) to the slanting plate rope hole (51) The space vector from the sliding rope hole (52) to the joint rotation center j In the initial state, the space vector from the sliding rope hole (52) to the first base rope hole (53) is

[0020] Furthermore, the process of solving the stiffness using the particle swarm algorithm includes:

[0021] Construct the basic equations of the joint geometry variable pulley system l j =L j (f j )·q; where L j (f j ) is the driving rope length l corresponding to the joint angular displacement q to the geometrically variable pulley j j The Jacobian matrix of ;

[0022] According to the basic equation of geometric variable pulley set, the basic structural parameter set of joint angle-rope tension is constructed;

[0023] Constructing joint kinematic transformation equations Among them, R j is the basic structural parameter set of the variable geometry pulley;

[0024] Initialize particle swarm variable P;

[0025] When the joint potential energy does not converge or the number of iterations does not exceed the upper limit, the table lookup method is used to find and interpolate the data corresponding to the variable P in the basic structure parameter set and substitute it into the joint kinematic transformation equation. Solve the joint potential energy and finally solve the optimal joint parameters;

[0026] Substitute into the joint stiffness equation K j , solve for the joint stiffness.

[0027] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0028] 1. The variable stiffness joint provided by the present invention is provided with several groups of geometrically variable pulley groups between the base and the slanted plate. Under the antagonistic action of the joint driving rope, the geometrically variable pulley groups will undergo controlled deformation, thereby changing the triangular shape formed by the rope holes, thereby changing the direction and the length of the lever arm of the force generated by the rope on the rope holes of the slanted plate. When the downward pulling force on the rope increases, the length of the lever arm of the torque generated on the center of the joint will increase. Because the force of the rope increases, the torque generated by the overall geometrically variable pulley group on the center of the joint will double, so that the joint has a larger joint stiffness change range, and when the joint is disturbed by the outside world, its joint stiffness will increase with the increase of the external disturbance, and it has stronger stability.

[0029] 2. The variable stiffness joint provided by the present invention is composed of a component with regular elasticity (i.e., a spring) and a rigid body component. Its mechanical model is easy to calculate, and thus can achieve precise control of physical properties such as joint posture and stiffness. In this way, the parameters of the motor driver can be calculated according to the stiffness requirements, and then the joint can be driven accurately; it is also convenient to optimize the mechanical structure and parameters of the joint.

[0030] 3. The variable stiffness joint provided by the present invention can be used for the joint part of the rope-driven serpentine robot arm for maintenance in complex environments. This type of working environment has additional requirements on the flexibility, adaptability and carrying capacity of the robot arm; it can also be used for adaptive exploration of difficult-to-model environments such as ruins detection. This type of working environment requires the robot arm to have the ability to adaptively change its posture according to the environment, and also requires the robot arm to have a certain carrying capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic structural diagram of a variable stiffness joint of the present invention;

[0032] Figure 2 yes Figure 1 Schematic diagram of the structure of the middle cross hinge;

[0033] Figure 3 A schematic diagram of the structure of a variable geometry pulley block of the present invention;

[0034] Figure 4 is a partial cross-sectional view of a variable stiffness joint of the present invention;

[0035] Figure 5 is another angle structural schematic diagram of the variable stiffness joint of the present invention;

[0036] Figure 6 It is a schematic diagram of the process of changing the joint stiffness of the variable geometry pulley assembly of the present invention under the action of the driving rope;

[0037] Figure 7 It is a schematic diagram of the deformation of the variable geometry pulley block of the variable stiffness joint of the present invention when it is disturbed by the outside world;

[0038] Figure 8 It is the stiffness algorithm framework of the variable stiffness joint proposed by the present invention;

[0039] Fig. 9 It is the basic structure of the variable geometry pulley block in the variable stiffness joint proposed by the present invention.

[0040] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0041] 1- angular displacement sensor; 2- cross hinge; 3- swash plate; 4- base; 5- variable geometry pulley block;

[0042] 21-upper gear; 22-cross shaft; 23-lower gear; 31-rotating gear; 41-base tray;

[0043] 51 - inclined plate rope hole; 52 - sliding rope hole; 53 - first base rope hole; 54 - second base rope hole; 55 - spring; 56 - rope; 57 - slide rail; 58 - sliding seat. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. 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. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] See also Figure 1-5 The present invention provides a variable stiffness joint, including a base 4, a swash plate 3, a cross hinge 2 and a plurality of sets of geometrically variable pulley sets 5; a base tray 41 is provided on the base 4 for rotationally connecting with the cross hinge 2; the cross hinge 2 is also rotationally connected with the swash plate 3.

[0046] The variable geometry pulley block 5 comprises a rope 56, a swash plate rope hole 51 disposed below the swash plate 3, a first base rope hole 53 and a second base rope hole 54 disposed at the bottom of the base 4, a slide rail 57 fixed between the bottom of the base 4 and the base tray 41, and a sliding seat 58 and a spring 55 sleeved on the slide rail 57; the spring 55 is located between the sliding seat 58 and the bottom of the base 4; and a sliding rope hole 52 is disposed on the sliding seat 58. One end of the rope 56 is fixed to the sliding seat 58, and then passes through the first base rope hole 53, the swash plate rope hole 51, the sliding rope hole 52 and the second base rope hole 54 in sequence, and the end thereof is connected to the motor, so as to adjust the position of the swash plate 3 through the rope 56.

[0047] With such a configuration, the extension and contraction of the rope 56 is driven by the motor. For example, when the rope 56 of one set of variable geometry pulleys 5 is pulled downward (i.e., the force on the rope is increased), the spring 55 will be further compressed as the rope force increases. At this time, the rope between the swash plate rope hole 51 and the sliding rope hole 52 will become more and more "vertical" because the sliding rope hole moves downward, and the arm length of the torque generated by the force on the rope 56 on the joint center will increase. Because the force of the rope 56 increases, the torque generated by the variable geometry pulley 5 on the joint center as a whole will double. After the swash plate 3 is pulled by the rope 56, it will rotate relative to the cross hinge 2, thereby achieving posture adjustment.

[0048] The rope 56 from the fixed point on the sliding seat 58 to the first base rope hole 53 and the rope 56 from the sliding rope hole 52 to the second base rope hole 54 are parallel to each other. Figure 5 As shown, an inclined slide rail 57 is provided between the bottom of the base 4 and the top of the base tray 41, and a sliding seat 58 is slidably sleeved on the slide rail 57. One end of the sliding seat 58 that slides downward fixes the initial end of the rope 56, and then a sliding rope hole 52 is provided through the sliding seat 58 along the direction of the slide rail 57. The first base rope hole 53 and the second base rope hole 54 are both provided at the lower end of the slide rail 57, so that the rope 56 here can always remain substantially parallel to the slide rail 57. The second base rope hole 54 penetrates downward through the bottom of the base 4, and the first base rope hole 53 opens upward at the bottom of the base 4, so that the rope 56 goes upward to the swash plate rope hole 51. In particular, when the swash plate 3 and the base 4 are parallel, the straight line formed by the first base rope hole 53 and the swash plate rope hole 51 is substantially perpendicular to the base. Since the position of the rope hole directly affects the magnitude and direction of the force acting on the swash plate 3 by the rope, in practical applications, the positions of the above rope holes can be optimized according to the target stiffness requirements.

[0049] In particular, the variable geometry pulleys 5 are three groups, which are equally spaced between the base 4 and the swash plate 3. Through the coordinated regulation of the three variable geometry pulleys 5, the regulation stability and flexibility of the joint can be improved, and the stiffness range can be improved.

[0050] The base tray 41 on the base 4 extends upward, and a bearing hole is set at the top to cooperate with the cross hinge 2. The base tray 41 is usually set in the middle of the base 4. In order to facilitate the installation of the slide rail 57, the side of the base tray 41 can be set as an inclined structure. The lower end of the slide rail 57 is located at the edge of the base 4, and the upper end is located above the base tray 41, so that the slide rail 57 can be tilted upward. The joint stiffness can also be adjusted by adjusting the tilt angle.

[0051] like Figure 2 As shown, the middle part of the cross hinge 2 is provided with a cross shaft 22, which is used to cooperate with the base tray 41 and the swash plate 3 to achieve relative rotation. The top and bottom of the cross hinge 2 are also provided with an upper gear 21 and a lower gear 23, respectively. The swash plate 3 is provided with a rotating gear 31 meshing with the upper gear 21, and the bottom of the base 4 is provided with a gear meshing with the lower gear 23; the meshing parts of the upper gear 21 and the lower gear 23 are respectively provided with an angular displacement sensor 1. The two groups of joint angular displacement sensors 1 arranged on the cross hinge 2 are connected to the swash plate 3 and the base 4 respectively by means of gear transmission, so as to transmit the relative angular displacement between the cross hinge 2 and the swash plate 3 and the base 4 to the sensor side.

[0052] The movement of the swash plate 3 is transmitted to the rotating gear 31, which in turn drives the rotation of the upper gear 21. When the swash plate 3 rotates around the cross shaft 22 on the cross hinge 2, it will also produce relative movement with the sensor bracket extending from the cross hinge. This relative movement can be collected by the angular displacement sensor 1 after being amplified by the gear. Under the action of the spatial force generated by the driving rope 56 on the swash plate 3, the cross hinge 2 and the base 4 rotate relative to each other in one direction, and relative rotation with the swash plate 3 in another direction. Therefore, there is movement in two directions between the base 4 and the swash plate 3, and the control flexibility is higher.

[0053] The variable stiffness joint provided by the present invention belongs to a fully active serpentine arm, that is, each joint is independently connected to a group of motors during use, and is easy to model, thereby facilitating accurate calculation and regulation of stiffness.

[0054] like Figure 3 As shown in FIG. 1 , the working principle of the present invention is as follows: when the variable geometry pulley block 5 is pulled by the rope 56 and deformed, the sliding rope hole 52 will move toward the base rope hole 54 under the action of the rope 56, thereby changing the triangular shape formed by the rope holes, thereby changing the direction of the force generated by the rope 56 on the swash plate rope hole 51, and changing the length of the force arm of the rope on the swash plate 3, as shown in FIG. Figure 3When the rope 56 of the variable geometry pulley block 5 is pulled and moves, and the pulley block is deformed, the tension generated by the rope section between the sliding rope hole 52 and the swash plate rope hole 51 will increase the force arm of the cross hinge 2, thereby increasing the torque generated by the rope on the swash plate to resist external disturbances.

[0055] like Figure 7 As shown, when the joint is disturbed by the outside world, if the rope is not actively adjusted, the variable geometry pulley set 5 will be deformed to a certain extent according to the degree of external disturbance. At this time, 1 to 2 of the 3 variable geometry pulley sets of the joint will be under tension, and the rest will be under compression. The pulley set that is deformed by traction will generate an additional torque on the center of the joint that increases with the increase of the disturbance, while the remaining pulley sets will generate a torque that decreases with the increase of the disturbance. The direction of these torques after superposition is opposite to the direction of the external torque on the joint, which can offset the disturbance caused by the external force on the joint, thereby increasing the stiffness of the joint.

[0056] Figure 8 The stiffness determination method of the variable geometry pulley proposed in the present invention is shown, which is specifically manifested as follows: when the joint is in a state of no external load, internal tension is balanced and local energy is minimum, a small torque in a specified direction is applied to the joint, and the joint will deflect. The deflection is in the same direction as the applied torque, and the ratio of the deflection to the torque is the joint stiffness.

[0057] When a joint is deflected by an external force, the elastic elements in the joint will deform to adapt to the structural changes, while storing or releasing a certain amount of energy. At the moment of deflection, the energy stored in the joint as a whole will instantly rise to a larger value, and then gradually slide to a lower value in the process of force balance by the various geometrically variable pulleys inside the joint. If the equation between the joint angle and the total energy of the joint is constructed based on the relationship between the elastic potential energy stored by the ropes and elastic elements of each group of geometrically variable pulleys in the joint and the deflection angle of the joint, and then by optimizing the solution to minimize the total energy of the joint, the deflection angle of the joint can be calculated according to the size of the external disturbance torque, and then the relationship between the joint stiffness and the rope tension and the external disturbance torque can be obtained.

[0058] The stiffness adjustment method proposed in the present invention is implemented as follows:

[0059] according to Fig. 9 The basic structure of the geometrically variable pulley block is shown, and the rope-pulley block node linkage equation is established as follows:

[0060]

[0061]

[0062] where Δxj is the compression of the spring in the variable geometry pulley j, is the tension on the rope in j, ∠SMO is the angle formed by the swash plate rope hole 51, the sliding rope hole 52 and the rotation center of the joint, is the initial preload on the rope in j, K S The joint rotation center refers to the rotation axis center of the swash plate 3.

[0063] S j is the torque exerted by the rope on the joint in the variable geometry pulley j, is the space vector from the first base rope hole 53 to the swash plate rope hole 51 in j, is the space vector from the first base rope hole 53 to the joint rotation center, is the space vector from the sliding rope hole 52 to the swash plate rope hole 51, is the space vector from the sliding rope hole 52 to the rotation center of the joint.

[0064] l j is the length of the driving rope corresponding to the geometrically variable pulley block j, j is the spatial vector of the sliding rope hole 52 to the first base rope hole 53 in the initial state, l dj j is the fixed length of the rope in the drive transmission part, q is the joint angular displacement, L j (f j ) is from q to l j The Jacobian matrix of .

[0065] From the above formula, the relationship between the force acting on the swash plate 3 in the joint and the cable tension can be constructed.

[0066] The joints are modeled using the robot arm DH parameter method as follows:

[0067]

[0068] c(θ)=cosθ i ; s(θ) = sinθ i ;

[0069] c(α)=cosα i-1 ; s(α) = sinα i-1

[0070] in

[0071]

[0072] On this basis, the kinematic equation of the joint is constructed as follows:

[0073]

[0074] Where R is the joint origin rotation transformation matrix, and r is the joint origin offset matrix.

[0075] Combined with the rope-pulley node linkage equation established in the previous article, the Jacobian matrix J from the joint drive rope to the joint posture can be constructed l as follows:

[0076]

[0077] Wherein, L refers to the formula l j =L j (f j )·q by L j (f j ), that is, is the transformation matrix from the joint driving rope to the joint angle.

[0078] According to the joint kinematic transformation process described above, based on the virtual displacement method, the joint energy conservation equation can be established as follows:

[0079]

[0080] where f T is the driving rope tension, δl is the driving rope displacement, S e T is the external torque on the joint, δq is the angular displacement of the joint, δx s is the spring compression. The spring stiffness K is introduced into this equation s , Rope stiffness K c , and transform the equation to derive the joint stiffness K j The equation is as follows:

[0081]

[0082] The formulas mentioned above show that the joint stiffness can be adjusted by adjusting the driving rope tension, driving rope displacement, spring stiffness, and joint geometry, and the relationship between them can be analyzed according to the formulas mentioned above. However, it can be seen from the joint stiffness equation that the joint stiffness is directly related to the rope tension on the joint, the rope stiffness, and the spring stiffness inside the joint, and they are coupled to each other, which makes it difficult to directly solve the joint stiffness through the above equations. In engineering applications, simulation and numerical fitting methods are often used to solve this type of complex coupling variable relationship.

[0083] Based on the above equations, the present invention innovatively introduces a particle swarm optimization solution algorithm, and establishes a multi-dimensional state set of joints by solving the states of each group of geometrically variable pulleys in the joint under different joint angles and rope tensions. The particle swarm method is used here to solve the joint state and further solve the joint stiffness with the basic structure of the joint as the constraint and the joint potential energy minimization as the solution goal. The core formula of this method is the joint elastic potential energy formula, such as:

[0084]

[0085] Where E is the elastic potential energy of the joint, K S is the stiffness of the spring, x s is the compression of the spring, K c is the rope stiffness, l is the compression of the driving rope; it is mainly composed of the elastic potential energy stored in the spring and the elastic potential energy stored in the rope. When the joint is subjected to external impact, it absorbs energy while causing elastic deformation of the joint driving rope and spring, and at this time, the elastic potential energy inside the joint will produce a step. Due to the friction between the components inside the joint, the elastic potential energy of the joint will gradually decrease until a stable state, which is the target state to be solved. The specific implementation process is as follows:

[0086]

[0087] Among them, the basic parameter set R of the joint angle-rope tension space j The space vector from the first base rope hole (53) to the swash plate rope hole (51) in the geometrically variable pulley block j is included. The space vector from the first base rope hole (53) to the joint rotation center The space vector from the sliding rope hole (52) to the slanting plate rope hole (51) The space vector from the sliding rope hole (52) to the joint rotation center j In the initial state, the space vector from the sliding rope hole (52) to the first base rope hole (53) is

[0088] The joint stiffness is determined according to the above method, and the driving parameters of the joint can be adjusted according to the stiffness, and the structural optimization design can also be performed.

[0089] In summary, the present invention provides a rope-driven joint with a large controllable joint stiffness variation range and a control method thereof. Under the antagonistic action of the joint driving rope, the geometrically variable pulley group will undergo controlled deformation, and the degree of deformation can be calculated according to the tension on the rope, the displacement of the rope, and the angular displacement fed back by the joint angular displacement sensor. The control method mainly includes a stiffness determination method for this type of variable stiffness joint, which is specifically manifested in the inverse kinematics calculation process based on the joint angular displacement-rope displacement, introducing the transformation equation of the geometrically variable pulley group, and establishing the joint energy transformation equation through the virtual displacement principle. Based on the principle of local minimization of joint energy, the particle swarm optimization method is used to solve the joint posture. The present invention overcomes the shortcomings of the variable stiffness rope-driven joint modeling and control difficulties and the small stiffness variation range in the prior art, and provides a variable stiffness joint that is easy to model, controlled, and has a large joint stiffness variation range, thereby constructing a fully driven rope-driven serpentine manipulator with both flexibility, adaptability, and load-bearing capacity.

[0090] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A variable stiffness joint, characterized in that: It comprises a base (4), a swash plate (3), a cross hinge (2), a plurality of sets of geometrically variable pulley sets (5) and a motor; The base (4) is provided with a base tray (41) for rotationally connecting with the cross hinge (2); the swash plate (3) is rotationally connected with the cross hinge (2); The variable geometry pulley block (5) comprises a rope (56), a swash plate rope hole (51) arranged below the swash plate (3), a first base rope hole (53) and a second base rope hole (54) arranged at the bottom of the base (4), a slide rail (57) fixed between the bottom of the base (4) and the base tray (41), and a sliding seat (58) and a spring (55) sleeved on the slide rail (57); the spring (55) is located between the sliding seat (58) and the bottom of the base (4); the sliding seat (58) is provided with a sliding rope hole (52); One end of the rope (56) is fixed on the sliding seat (58), and then passes through the first base rope hole (53), the swash plate rope hole (51), the sliding rope hole (52) and the second base rope hole (54) in sequence, and the rear end is connected to the motor, so as to adjust the position of the swash plate (3) through the rope (56).

2. The variable stiffness joint according to claim 1, characterized in that: The rope (56) from the fixed point on the sliding seat (58) to the first base rope hole (53) and the rope (56) from the sliding rope hole (52) to the second base rope hole (54) are parallel to each other.

3. The variable stiffness joint according to claim 1, characterized in that: The variable geometry pulley groups (5) are in three groups and are distributed at equal intervals between the base (4) and the swash plate (3).

4. The variable stiffness joint according to claim 1, characterized in that: An upper gear (21) and a lower gear (23) are respectively provided at the top and bottom of the cross hinge (2), a rotating gear (31) meshing with the upper gear (21) is provided on the swash plate (3), and a gear meshing with the lower gear (23) is provided at the bottom of the base (4).

5. The variable stiffness joint according to claim 4, characterized in that: Angular displacement sensors (1) are respectively provided at the meshing positions of the upper gear (21) and the lower gear (23).

6. A method for determining the stiffness of a variable stiffness joint according to any one of claims 1 to 5, characterized in that: include: The joint stiffness equation and joint multi-dimensional state set shown in (1) are constructed, and then the particle swarm algorithm is used in this set, with the basic structure of the joint as the constraint and the minimization of the joint potential energy as the solution goal, to solve the joint state, and then substitute it into the joint stiffness equation to obtain the joint stiffness: Among them, K j is the joint stiffness, K S is the stiffness of the spring, K c is the cable stiffness, f is the tension on the driving cable, Jl is the Jacobian matrix of the joint pose, J l T is the transpose of the Jacobian matrix, and q is the joint angular displacement.

7. The method for determining stiffness according to claim 6, characterized in that: The joint potential energy is shown in formula (2): Where E is the joint potential energy, K S is the stiffness of the spring, x s is the compression of the spring, K c is the rope stiffness, and l is the elongation of the driving rope.

8. The method for determining stiffness according to claim 6, characterized in that: The multi-dimensional state set of the joint includes a basic structural parameter set of a geometrically variable pulley set, a DH parameter set and a particle swarm parameter set.

9. The method for determining stiffness according to claim 8, characterized in that: The basic structural parameter set of the geometrically variable pulley block includes the space vector from the first base rope hole (53) to the swash plate rope hole (51) in the geometrically variable pulley block j. The space vector from the first base rope hole (53) to the joint rotation center The space vector from the sliding rope hole (52) to the slanting plate rope hole (51) The space vector from the sliding rope hole (52) to the joint rotation center j In the initial state, the space vector from the sliding rope hole (52) to the first base rope hole (53) is 10. The stiffness determination method according to any one of claims 6 to 9, characterized in that: The process of solving the stiffness using the particle swarm algorithm includes: Construct the basic equations of the joint geometry variable pulley system l j =L j (f j )·q; where L j (f j ) is the driving rope length l corresponding to the joint angular displacement q to the geometrically variable pulley j j The Jacobian matrix of ; According to the basic equation of geometric variable pulley set, the basic structural parameter set of joint angle-rope tension is constructed; Constructing joint kinematic transformation equations Among them, R j is the basic structural parameter set of the variable geometry pulley; Initialize particle swarm variable P; When the joint potential energy does not converge or the number of iterations does not exceed the preset value, the table lookup method is used to find and interpolate the data corresponding to the variable P in the basic structure parameter set and substitute it into the joint kinematic transformation equation. Solve the joint potential energy and finally solve the optimal joint parameters; Substitute into the joint stiffness equation K i , solve for the joint stiffness.

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