Flexible regulation and control method for combined six-rod multiple metamorphic mechanism

Abstract

The invention discloses a compliance regulation and control method for a combined six-bar multiple metamorphic mechanism. The combined six-bar multiple metamorphic mechanism is formed by combining two of the following three four-bar mechanisms: a Bennett mechanism, a parallelogram mechanism and a spherical four-bar mechanism. The compliance regulation and control method is realized by increasing the degree of freedom of the combined six-bar multi-metamorphic mechanism, and comprises the following steps: A, selecting two configurations needing to be switched; b, motion states of all joints of the mechanism under the two configurations in the step A are analyzed, and mutant joints and non-mutant joints are determined; c, part of non-mutant joints are selected to be fixed at non-bifurcation points, additional joints are added, and configuration switching is achieved; and D, each additional joint is coupled to the corresponding mutation joint adjacent to the additional joint, and a coupling joint is formed. The bifurcation points are converted into the continuous motion interval through bifurcation domain expansion, the mechanism achieves dynamic and flexible conversion in motion in combination with the coupling joint design, the shutdown requirement of traditional rigid switching is avoided, and motion impact is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of mechanism and metamorphic mechanism, and particularly relates to a compliant regulation method for a combined six-bar multi-metamorphic mechanism. BACKGROUND

[0002] For most metamorphic mechanisms, the motion branch is single degree of freedom, and becomes instantaneous multiple degrees of freedom at the bifurcation point when the configuration is converted. It is this feature that leads to the non-smooth and non-fluent of the mechanism during the configuration conversion. The existing researches rarely involve the conversion between configurations, and the commonly used configuration conversion method is to move the mechanism to the bifurcation point and keep it stationary, and then control the newly added instantaneous degree of freedom through an additional drive, so as to realize the configuration conversion.

[0003] The current compliant control of robots is mainly used for controlling force and position, and is mainly divided into active compliant control and passive compliant control. There are few studies on the compliant conversion between multiple configurations of metamorphic mechanisms, and the compliant conversion between configurations of metamorphic mechanisms pays more attention to reducing the impact of force and the influence of mechanical structure precision on the position of the bifurcation point.

[0004] The disadvantages of the prior art are:

[0005] 1. The bifurcation point depends on rigid constraints, and the conversion process is not compliant: configuration switching needs to be stopped at the bifurcation point, and is forcibly completed through mechanical limiting or locking devices, resulting in motion impact and energy mutation.

[0006] 2. The conversion path is single and cannot be dynamically adjusted: the geometric conditions of the bifurcation point are strict, and the mechanism can only switch according to the preset path and cannot adapt to dynamic working conditions.

[0007] 3. The additional drive depends on the system complexity: additional drivers or sensors are needed to control the bifurcation point, resulting in increased system complexity and cost.

[0008] Therefore, it is a problem to be solved in the industry to provide a compliant regulation method for dynamic adaptation, low-impact continuous switching between multiple configurations. SUMMARY

[0009] In order to solve the problems in the prior art, the main purpose of the present application is to provide a compliant conversion method for expanding the bifurcation point into a bifurcation domain, so as to realize dynamic adaptation, low-impact continuous switching between multiple configurations.

[0010] In order to achieve the above main purpose, the present application discloses a compliant regulation method for a combined six-bar multi-metamorphic mechanism, which is composed of two of the following three four-bar mechanisms:

[0011] Bennett mechanism, parallelogram mechanism, spherical four-bar mechanism;

[0012] The compliant control method is achieved by increasing the degrees of freedom of the combined six-bar multi-variable structure, and includes the following steps:

[0013] A. Select the two configurations that need to be switched;

[0014] B. Analyze the motion state of each joint of the mechanism under the two configurations in step A to determine the mutant joints and non-mutant joints;

[0015] C. Select some non-mutated joints and fix them at non-bifurcation points, add additional joints, and achieve configuration switching;

[0016] D. Couple each additional joint to its adjacent mutant joint to form a coupled joint.

[0017] In this invention, the combined six-bar multivariable structure is a line-symmetric Bricardian mechanism, composed of three types of four-bar mechanisms: the Bennett mechanism, the parallelogram mechanism, and the spherical four-bar mechanism. Based on the commonalities of these three types of mechanisms, they can be combined in pairs to form different six-bar mechanisms.

[0018] Each motion branch of the combined six-bar multivariable mechanism has a single degree of freedom, and its motion trajectory in space consists of multiple intersecting closed-loop curves, with the intersection point being the bifurcation point. Since different motion branches are not tangent (and cannot be tangent) at the bifurcation point, the motion trajectory changes abruptly when the mechanism transitions at the bifurcation point, resulting in impacts during the mechanism's motion. To make the transition process smoother, this invention employs an added degree of freedom method, expanding the bifurcation point into a bifurcation domain, allowing the mechanism sufficient space for motion branch transitions.

[0019] It is important to note that the smooth transition of the joint state needs to occur before the bifurcation point, but it needs to be controlled within a certain range to avoid the addition of degrees of freedom affecting the normal movement state of the motor branch.

[0020] According to a specific embodiment of the present invention, in step C, two non-mutational joints are selected and fixed at non-bifurcation points to add additional joints. It should be noted here that the degrees of freedom of the closed-loop mechanism must meet certain conditions; adding a joint does not necessarily add a degree of freedom. The joints need to be added in appropriate positions to meet the requirements for increasing the degrees of freedom.

[0021] According to one specific embodiment of the present invention, the additional joints are any form of kinematic pair, and the number is 1-2.

[0022] According to a specific embodiment of the present invention, in step C, the position of the additional joint is determined according to the following principle: the degree of freedom of the fixed mechanism is increased by 1; after the mechanism fixes some joints at non-bifurcation points, the degree of freedom is 0; after adding the additional joint, the degree of freedom of the mechanism becomes 1.

[0023] The mechanism with the addition of extra joints can switch from one configuration to another while some joints are fixed.

[0024] According to a specific embodiment of the present invention, in step D, the coupling joint includes two rotating joints that are coupled to each other, and the axes of the two rotating joints are perpendicular to each other.

[0025] According to one specific embodiment of the present invention, the coupled joint includes two degrees of freedom; due to the geometric constraints of the joint, the range of motion of one degree of freedom is determined by the position of the other degree of freedom.

[0026] According to a specific embodiment of the present invention, in step C, two non-mutant joints are selected and fixed, and one of the remaining joints is replaced with a ball joint.

[0027] The present invention has the following beneficial effects:

[0028] This invention exhibits significant advantages over existing technologies. By expanding the bifurcation point and transforming the instantaneous switching point into a continuous switching interval, combined with a coupled joint design, the newly added degrees of freedom in the non-switching state are constrained, enabling the mechanism to achieve dynamic and compliant transitions during motion. This avoids the shutdown requirements of traditional rigid switching and significantly reduces motion impact. This invention breaks through the limitations of traditional variable-cell mechanisms that rely on rigid constraints and multiple redundant drives, providing a multifunctional and low-cost innovative solution for fields such as flexible manufacturing.

[0029] To more clearly illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0030] Figure 1A This is a schematic diagram of the parallelogram mechanism that makes up the six-bar linkage in Example 1;

[0031] Figure 1B This is a schematic diagram of the equilateral Bennett mechanism that makes up the six-bar linkage in Example 1;

[0032] Figure 1C This is a schematic diagram of the combined six-bar multi-variable cell mechanism in Example 1;

[0033] Figure 2 This is a schematic diagram of the motion path and bifurcation point of the six-bar linkage in Example 1;

[0034] Figure 3 This is a flowchart of the addition of degrees of freedom method in Example 1;

[0035] Figure 4This is a schematic diagram of the transition between motion branch 1 and motion branch 4 of the six-bar linkage at bifurcation point 1 in Embodiment 1;

[0036] Figure 5 This is a schematic diagram of the mechanism using the added degrees of freedom method in Example 1;

[0037] Figure 6 This is a schematic diagram of the compliant motion branching method in Example 1;

[0038] Figure 7A1 This is a schematic diagram of a single cut in the coupling joint design of Example 1;

[0039] Figure 7A2 When cutting once, and Relationship diagram;

[0040] Figure 7B1 This is a schematic diagram of multiple continuous cuts in the coupling joint design of Example 1;

[0041] Figure 7B2 When making multiple consecutive cuts, and Relationship diagram;

[0042] Figure 8 This is a schematic diagram of the mechanism parameters in Example 1;

[0043] Figure 9A In the equivalent mechanism of Embodiment 1, the rotation range of θ3 relative to θ2;

[0044] Figure 9B In the equivalent mechanism of Embodiment 1, the rotation range of γ1 relative to θ2;

[0045] Figure 10A In the equivalent mechanism of Embodiment 1, the rotation range of θ3 relative to θ1 and θ2;

[0046] Figure 10B In the equivalent mechanism of Embodiment 1, the rotation range of γ1 relative to θ1 and θ2;

[0047] Figure 11 This is a comparison diagram between the traditional conversion and the flexible conversion of Example 1;

[0048] Figure 12A This is a photograph of the compliant cellular mechanism of Example 1;

[0049] Figure 12B This is a 3D model diagram of the compliant variable cell mechanism of Example 1;

[0050] Figure 13A This is a schematic diagram of the coupling joint in Example 1;

[0051] Figure 13B This is a schematic diagram of the structure of a common joint;

[0052] Figure 14 This is a schematic diagram of the overall assembly of the compliant variable cell mechanism prototype of Example 1;

[0053] Figure 15A This is the six-bar linkage of Example 1, and the conventional transformation diagram of motion branch 4 to motion branch 1;

[0054] Figure 15B This is a diagram showing the compliant transition of motion branch 4 to motion branch 1 in the six-bar linkage of Example 1. Detailed Implementation

[0055] Many specific details are set forth in the following description in conjunction with embodiments in order to provide a full understanding of the invention. However, it should be understood that the following embodiments and detailed descriptions are for illustrative purposes only and do not limit the scope of protection of the invention.

[0056] Example 1

[0057] This embodiment provides a compliant control method for a combined six-bar multi-variable cell mechanism (hereinafter referred to as "six-bar mechanism"), which is composed of two of the following three types of four-bar mechanisms:

[0058] Bennett mechanism, parallelogram mechanism, spherical four-bar mechanism;

[0059] This compliant control method is achieved by increasing the degrees of freedom of the combined six-bar multi-variable structure, and includes the following steps:

[0060] A. Select the two configurations that need to be switched;

[0061] B. Analyze the motion state of each joint of the mechanism under the two configurations in step A to determine the mutant joints and non-mutant joints;

[0062] C. Select some (e.g., two) non-mutational joints and fix them at non-bifurcation points (the degree of freedom is reduced by one), and add two additional joints (the degree of freedom is increased by one) to achieve configuration switching; both additional joints are revolute joints and are symmetrically arranged.

[0063] D. Couple each additional joint to its adjacent joint to form a coupled joint; the two coupled joints are identical and each includes two mutually coupled revolute joints.

[0064] In step C, the position of the additional joint is determined according to the following principles: the degree of freedom of the fixed mechanism is increased by 1; after the mechanism fixes some joints at non-bifurcation points, the degree of freedom is 0; after adding the additional joint, the degree of freedom of the mechanism becomes 1.

[0065] In step C, an additional joint is set at each symmetrical position. Theoretically, the two additional joints can also be asymmetrical, but this would make the calculations very complicated.

[0066] In step D, the coupled joint includes two degrees of freedom; due to the geometric constraints of the joint, the range of motion of one degree of freedom is determined by the position of the other degree of freedom.

[0067] This embodiment selects a parallelogram mechanism ( Figure 1A ) and Bennett's organization ( Figure 1B A six-bar linkage (combined) Figure 1C We will conduct an in-depth analysis. Figures 1A-1C This describes the evolution of this type of variable-cell mechanism, where numbers represent joints, letters represent links, and α... ij θ represents the torsional angle of joint j relative to joint i. i a represents the rotation angle of joint i. ij This represents the length of the link between joints i and j. Using link F as the base, a coordinate system is established as shown in the figure, with the DH parameters as follows.

[0068] a 12 =a 45 =a+b,a 23 =a 34 =b,a 51 =a 61 =a

[0069] α 12 =α 45 =-β,α 23 =α 56 =β,α 34 =α 61 =0

[0070] Analysis and verification revealed that the mechanism has 5 different types of motion branches (MB1-5) and 4 bifurcation points (SC1-4), with 10 independent motion paths (MP1-10), such as... Figure 2 As shown, the topological relationships are shown in Table 1.

[0071] Table 1. Topological Relationship between Bifurcation Points and Independent Motion Paths

[0072]

[0073] The topological relationship between motion paths and bifurcation points is shown in Table 1. 1 indicates that the motion path passes through this bifurcation point, and 0 indicates otherwise. Motion paths that pass through the same bifurcation point can be interchanged. Each motion branch of this type of variable-cell mechanism has a single degree of freedom, and its trajectory in space consists of multiple intersecting closed-loop curves, with the intersection point being the bifurcation point. Since different motion branches are not tangent at the bifurcation point (and cannot be tangent), the motion trajectory of the mechanism changes abruptly when transitioning at the bifurcation point, resulting in impact during the mechanism's motion. To make the transition process smoother, this patent employs an added degree of freedom method, expanding the bifurcation point into a bifurcation domain, allowing the mechanism sufficient space for motion branch transitions. The implementation method of the added degree of freedom method is as follows: Figure 3 As shown.

[0074] Next, we will select motion branch 1, motion branch 4, and bifurcation point 1 as the research scenario for trajectory smoothness. The specific implementation method and analysis process will be elaborated below.

[0075] like Figure 4 As shown in Table 2, the joints of the mechanism exhibit different motion states during motion branches 1 and 4. The key to smoothing the motion trajectory lies in achieving a smooth transition between the states of abrupt joints. Abrupt joints include two types: one transitioning from rest to motion, and the other from motion to rest. Regardless of the type, during the dynamic transition, the abrupt joint will experience significant acceleration to complete the state change, leading to impact or jamming of the mechanism. A smooth transition process should involve the immobile joints gradually accelerating while the movable joints gradually decelerate until they match the motion state of the transformed motion branch, thus completing the transition.

[0076] Table 2 shows the joint motion states of kinematic branches 1 and 4 before and after the bifurcation point 1.

[0077]

[0078] In this motion branch transition scenario, a compliant transition trajectory requires the simultaneous movement of all aberration joints, which is impossible in motion branches 1 and 4. Therefore, a new degree of freedom needs to be introduced to achieve synchronization between the two.

[0079] The transition from motion branch 1 to motion branch 4, in the traditional method, requires the structure to reach the bifurcation point 1 before the transition can occur. To achieve a smooth transition in abrupt joints, the mechanism needs to begin the configuration transition before reaching the bifurcation point; at this point, joints 1 and 4 have not yet moved to their zero-angle positions. With joints 1 and 4 fixed, the four-bar linkage with joints 2, 3, 5, and 6 as revolute joints has zero degrees of freedom and cannot complete the transition between motion branch 1 and motion branch 4.

[0080] The method of adding degrees of freedom involves adding new revolute joints to enable the transition between motion branches. For example... Figure 5 As shown, two symmetrically placed revolute joints are added to this mechanism, located on the common perpendicular lines of joints 1 and 2, and joints 4 and 5, respectively. With joints 1 and 4 fixed, the six-bar linkage consisting of joints 2, 3, 5, 6, 7, and 8 can achieve the transition between motion branch 1 and motion branch 4. The smooth transition of the joint state needs to occur before the bifurcation point, but this needs to be controlled within a certain range to avoid the added degree of freedom affecting the normal motion state of the motion branch. For example... Figure 6 As shown, joint 2 is fixed in motion branch 1, and joint 3 is fixed in motion branch 4. The compliant transition from motion branch 1 to motion branch 4 should release the additional degree of freedom near the bifurcation point, allowing joints 2 and 3 to move simultaneously, with joint 2 decelerating and joint 3 accelerating. The additional degree of freedom should then be restricted upon transitioning to motion branch 4.

[0081] As shown in the equivalent six-bar linkage above, the rotation of the newly added joint is synchronized with the rotation of the two adjacent joints. Therefore, the newly added joint can be coupled to one of the adjacent joints. The degrees of freedom of the newly added joint are restricted by the motion position of the adjacent joint, allowing it to release when it moves close to the bifurcation point, thus enabling the transition of the motion branch in advance. After the transition of the motion branch is completed, it is restricted again. The design concept and specific parameter calculation of the coupled joint will be introduced next.

[0082] A coupled joint is defined as a complex kinematic pair composed of multiple kinematic pairs that are coupled to each other and have certain constraints. Its overall degree of freedom can change from single to multiple degrees of freedom, and it can also switch between different degree-of-freedom modes. The kinematic pairs are coupled to each other through geometric constraints, therefore no drive control coupling is required.

[0083] In this design, joints 2 and 7, and joints 5 and 8 are coupled. These two coupled joints are identical, consisting of two rotating pairs coupled together, with their axes perpendicular to each other. For example... Figure 7A1 As shown, a coupling joint is designed based on the Hooke pair. Part 3 is equivalent to the cross shaft of the Hooke pair, and parts 1 and 2 are connected to part 3 by revolute joints. The rotation angle of part 1 relative to part 3 is named... The rotation angle between part 2 and part 3 is named The starting coordinates are as follows Figure 7A2 As shown.

[0084] When the bottom surface of part 1 completely coincides with the top surface of part 3, the rotation between part 2 and part 3 is restricted; this is a single-degree-of-freedom state. For example...Figure 7A1 As shown, at this point, axis 1 coincides with axis 3. Using axis 1 as the axis of rotation, the bottom surface of part 1 rotates around axis 1 by a certain angle, removing a triangular prism region. At this time, the rotational degree of freedom between part 2 and part 3 is released, but the rotational range is less than the cutting angle. This degree of freedom is only released when angle 1 equals 0, because when part 1 rotates relative to part 3, i.e. When the value is not equal to 0, the uncut portion at the bottom of part 1 will restrict the rotation of angle 2, thus achieving a geometric constraint on angle 2. By rotating the object at a certain angle and repeating a similar cutting operation, you can... The range of rotation becomes continuous. Assuming the angle of each rotation is infinitesimally small, theoretically a smooth curve can be obtained. It is possible to obtain a continuous range of activity (e.g.) Figures 7B1-7B2 (As shown).

[0085] To facilitate understanding, the joint angles are redefined, such as... Figure 8 As shown. In the original mechanism corresponding to the equivalent mechanism, the angle θ1 of joint 1 is a parameter of the equivalent mechanism. This is beneficial for calculating the motion of the newly added degree of freedom, and transforming the two-degree-of-freedom mechanism into a single-degree-of-freedom mechanism for solution.

[0086] When θ1 = 45° is fixed, rotating θ2 yields the corresponding rotation angle curves for θ3 and γ1, as shown in Figure 9. It can be seen that with the addition of the joint, θ2 and θ3 can move simultaneously, and the rotation of the new joint γ1 will reset after completing the motion branch transition, without affecting the normal motion branch. Since joint 7 is located between joints 1 and 2, with joint 1 acting as the primary driver and joint 2 maintaining motion throughout motion branch 4, joint 7 is chosen to be coupled to joint 2, with joint 7 representing an additional degree of freedom.

[0087] Depend on Figure 9A It can be seen that the additional degrees of freedom create a triangular active region for joints 2 and 3. When θ1 = 45° is fixed, joints 2 and 3 can move along the line. To achieve free movement within the bifurcation domain, it is necessary to calculate all the spaces within the bifurcation domain. Using MATLAB for traversal calculations, the motion trajectories of all equivalent mechanisms with θ1 ranging from 0 to 90° can be derived, such as... Figure 10A As shown, this will facilitate the compliant changes of joints 2 and 3.

[0088] As the angle θ1 is gradually changed to zero, the curve gradually contracts, resulting in a bifurcation region, as shown below. Figures 10A-10B As shown. Figure 10A bifurcation domains and Figure 10BThe motion domains of γ1 are one-to-one, which means that the range of the bifurcation domain can be coupled and designed, and γ1 can be controlled by θ2.

[0089] like Figure 10B As shown, the newly added joints 7 and 8 only need to rotate a small angle to achieve a configuration transformation. Therefore, it is reasonable to design the newly added joints 7 and 8 in a coupled manner with other joints, strictly limiting their rotation to the process of motion branch transformation. This is the origin of the coupled joint. This coupled joint satisfies the degree of freedom requirements near the branch point while maintaining a single degree of freedom in the non-transformation state. Importantly, this does not rely on additional drives for locking or releasing; it depends entirely on its own motion state.

[0090] Coupled joints can only limit the rotational range of γ1, and cannot strictly limit it to a specific curve. Figures 10A-10B It can be seen that the bifurcation domain corresponding to the large angle θ1 completely includes the bifurcation domain corresponding to the small angle θ1. This indicates that the coupled joint designed for the large angle can be compatible with the variable axis joint at the small angle. When performing motion branch conversion, θ1 can maintain its motion state (angle decreases) without affecting the conversion effect. Thus, all joints can be converted while in motion.

[0091] like Figure 11 As shown, the red area represents the bifurcation region. The blue line represents the normal transition trajectory between motion branch 1 and motion branch 2, while the coupled joint can achieve a smoother motion trajectory (black line). As θ2 gradually increases, the range of θ3 gradually decreases, and the range of γ1 first increases and then decreases, indicating that the motion in this bifurcation region has self-convergence characteristics. That is, without additional drive, the mechanism can return to the normal motion branch after passing through the bifurcation region, improving the stability of the transition process between motion branches.

[0092] Based on the velocities of the mechanism before and after entering the bifurcation region, the velocities of joints θ2 and θ3 can be smoothly designed. Synchronizing the time of uniform acceleration of θ2 with the time of uniform deceleration of θ3 achieves a smoother transition between motion branches. Alternatively, the acceleration can be modified to a trapezoidal shape or a higher-order fitted curve to achieve an even smoother transition.

[0093] The mechanical structure design of this embodiment encompasses 3D modeling, parts machining, and assembly: During the modeling stage, the shape of the rods is optimized to avoid motion interference; the actual shape differs slightly from the initial model but retains the variable cell parameters; the positions of the coupling joints are adjusted to suit installation and drive requirements. 6065 aluminum alloy is used to achieve lightweighting; conventional joints (2 / 4 / 5) use steel clearance-fit bushings, while coupling joints (3 / 6) use brass contact surfaces to reduce friction. Axial accuracy is adjusted via threaded connections and locking nuts (Figure 13). During actual machining, the joints are translated along the axis; although the positions of additional joints are changed, the smooth transition characteristics of the motion branches are still maintained.

[0094] For drive selection, a servo motor was chosen to achieve precise control of the angle and speed of the active linkage. This servo motor features a built-in planetary reduction mechanism, providing a large driving torque (2.5 N·m), and also includes a built-in drive and magnetic encoder, allowing for multiple output modes and precise control of rotation angle and speed. A host computer was used to adjust and test the mechanism's motion parameters.

[0095] like Figures 12A-12B As shown, the physical assembly of the variable-cell mechanism is the same as that in the simulation. The experimental platform consists of two symmetrically placed optical platforms, with rod F serving as the base. One end of rod F is fixed to the bottom optical platform, and the other end is fixed to the upper optical platform. To avoid interference, the rod itself is omitted. The drive motor is installed between rod A and the upper optical platform; rod A is the drive rod.

[0096] In summary, the components and interrelationships of the prototype are as follows: Figure 14 As shown, it consists of several parts: a host computer, a servo motor, a power supply, and a prototype of the variable-cell mechanism.

[0097] Figures 15A-15B The image shows a comparison between the normal transition and the compliant transition between motion branch 4 and motion branch 1. Figure 15A It demonstrates the normal transition from motion branch 4 to motion branch 1, from a parallelogram mechanism to a Bennett mechanism, with the mechanism passing through bifurcation point 1. Figure 15B The demonstration shows the smooth transition from motion branch 4 to motion branch 1. It can be seen that the smooth transition bypasses the bifurcation point 1.

[0098] Example 2

[0099] The difference between this embodiment and Embodiment 1 is that in step C, two non-mutant joints are selected and fixed, and one of the remaining joints is replaced with a ball joint.

[0100] Although the present invention has been described above by way of embodiments, the above embodiments are only used to exemplify possible implementations of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions or changes made by those skilled in the art in accordance with the present invention should also be covered by the scope of protection defined by the claims of the present invention.

Claims

1. A compliant control method for a combined six-bar multi-variable-cell mechanism, wherein the combined six-bar multi-variable-cell mechanism is composed of two of the following three types of four-bar mechanisms: Bennett mechanism, parallelogram mechanism, spherical four-bar mechanism; Its features are, The compliant control method is achieved by increasing the degrees of freedom of the combined six-bar multi-variable structure, and includes the following steps: A. Select the two configurations that need to be switched; B. Analyze the motion state of each joint of the mechanism under the two configurations described in step A to determine the mutant joints and non-mutant joints; C. Select some of the non-mutation joints and fix them at non-bifurcation points, add additional joints, and realize configuration switching; D. Couple each of the additional joints to its adjacent mutant joint to form a coupled joint.

2. The compliance control method according to claim 1, characterized in that, In step C, two of the non-mutation joints are selected and fixed at non-bifurcation points to add additional joints.

3. The compliance control method according to claim 2, characterized in that, The additional joints are any type of kinematic pair, and the number is 1-2.

4. The compliance control method according to claim 3, characterized in that, In step C, the position of the additional joint is determined according to the following principles: the degree of freedom of the fixed mechanism is increased by 1; after the mechanism fixes some joints at non-bifurcation points, the degree of freedom is 0; after adding the additional joint, the degree of freedom of the mechanism becomes 1.

5. The compliance control method according to claim 1, characterized in that, In step D, the coupling joint includes two rotating joints that are coupled to each other, and the axes of the two rotating joints are perpendicular to each other.

6. The compliance control method according to claim 1, characterized in that, The coupled joint includes two degrees of freedom; due to the geometric constraints of the joint, the range of motion of one degree of freedom is determined by the position of the other degree of freedom.

7. The compliance control method according to claim 1, characterized in that, In step C, two of the non-mutant joints are selected and fixed, and one of the remaining joints is replaced with a ball joint.

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