Rigidity changing method and position control method of vine-imitating inflatable arm

Abstract

The invention provides a variable stiffness method and a position control method of a vine-imitating inflatable arm, and belongs to the technical field of soft robots. The tip of the inflation arm is turned outwards through the air pressure effect so as to extend to the expected length, the pressure difference in the annular variable-rigidity air bag around the arm rod is adjusted so as to control the local rigidity of the inflation arm, wrinkles can be generated at the position with the lowest rigidity in combination with a motor-rope device, and steering control over the inflation arm is achieved. When position control is carried out, on the basis of a tail end trajectory tracking task, a sequence control algorithm is adopted to carry out closed-loop control on all joints successively, and three criteria are established in the algorithm to help the tail end trajectory tracking task to be completed. The variable stiffness range of the vine-imitating inflatable mechanical arm is widened, a new manufacturing process is adopted, the level of tip movement can be improved, and the sequence control algorithm can help the inflatable arm to achieve accurate multi-joint parallel cooperative control.

Description

Technical Field

[0001] The present invention belongs to the technical field of soft robots, and specifically, relates to a variable stiffness method for a vine-like inflatable arm and a position control method therefor. Background Art

[0002] As an important branch of soft robots, the vine-like inflatable manipulator has continuous and compliant structural characteristics. It can be extended by turning the tip material outwards and retracted by turning the tip material inwards. The vine-like inflatable manipulator has nearly infinite degrees of freedom geometrically, but the actual controllable degrees of freedom are limited. Adding actuators according to the number of degrees of freedom will make the whole system overly complex and large. How to control more degrees of freedom with as few actuators as possible is one of the problems that must be solved in the current field of inflatable arms. The variable stiffness method can dynamically adjust the stiffness of the whole or part of the vine-like inflatable arm, making any area on the surface of the arm rod become the steering part, while the rest of the area maintains shape locking. Combining with the actuators arranged in parallel can realize the shape control process of the vine-like inflatable arm. Most of the existing variable stiffness methods need to introduce rigid structures, which is not conducive to the tip movement process of the vine-like inflatable arm in the compliant state, and there is still room for improvement in the variable stiffness range. Reducing the adverse impact of the variable stiffness method on the movement of the inflatable arm and increasing the variable stiffness range are of great significance to the control performance of the vine-like inflatable arm.

[0003] The structure of the vine-like inflatable arm with few actuators and many degrees of freedom cannot achieve multi-joint parallel cooperative control. To ensure the control accuracy, detailed control steps of the vine-like inflatable arm need to be given to achieve a more accurate solution process of kinematics and dynamics. Designing a control algorithm for the vine-like inflatable arm equipped with the variable stiffness method can provide important theoretical support and technical guarantee for the application of the inflatable arm in actual working conditions. Summary of the Invention

[0004] In summary, the present invention aims to design a variable stiffness method to increase the variable stiffness range of the vine-like inflatable manipulator and reduce the adverse impact caused by the rigid structure on the tip folding movement of the vine-like inflatable manipulator. Starting from the structural characteristics of the vine-like inflatable manipulator with few actuators and many degrees of freedom, a sequential control algorithm considering three-dimensional movement of multiple joints is designed to achieve precise multi-joint parallel cooperative control. Overall, a variable stiffness method for a vine-like inflatable arm and a position control method therefor are proposed.

[0005] The present invention is realized through the following technical solutions: A vine-like inflatable arm:

[0006] The vine-like inflatable arm includes a sealed base, an inflatable arm, and a recovery spool;

[0007] In the initial stage, the arm rod material of the inflatable arm is wound around the recovery spool. When the air pressure in the sealed base increases, the material of the inflatable arm will turn outwards, showing tip growth, and the inflatable arm will elongate.

[0008] The inflatable arm is composed of a plurality of annular variable-stiffness airbags distributed axially. Each annular variable-stiffness airbag includes an inner wall material of the inflatable arm, an outer wall material of the inflatable arm that wraps around the outside of the inner wall material and contacts the outside world, and a thin-layer multi-layer structure group located between the outer wall material and the inner wall material of the inflatable arm;

[0009] The main cavity area of the inflatable arm is formed by the inner wall material of the inflatable arm;

[0010] The multi-layer structure group includes a mixed material layer group and a same material layer group, which are arranged alternately along the circumferential direction, and there is a gap between adjacent layer groups;

[0011] The annular variable-stiffness airbag changes the friction state between the layer groups by adjusting the internal pressure difference, realizing the adjustable control of the local stiffness of the vine-like inflatable arm.

[0012] Further, the mixed material layer group is formed by stacking materials with different friction coefficients, with two rough material layers inside and a low-friction material layer outside;

[0013] The same material layer group is formed by stacking multiple thin layers of the same material.

[0014] Further, the multi-layer structure group is designed as a parallelogram structure. It is fixed between the inner wall material and the outer wall material of the inflatable arm through heat-sealing lines, and the layers overlap with each other to form air chambers to prevent the layer group from moving.

[0015] Further, the vine-like inflatable arm further includes three sets of motor-rope devices evenly arranged at 120° along the circumferential direction, where the motor is at the root of the arm rod, and the rope extends from the root to the tip of the arm rod;

[0016] When the pressure difference of a certain variable-stiffness airbag approaches zero, a steering joint is formed here. By contracting the rope, wrinkles are generated at the lowest stiffness, driving the inflatable arm to bend.

[0017] A variable-stiffness method for a vine-like inflatable arm: The variable-stiffness method includes the following steps:

[0018] Step 1: Pressurize the main cavity of the vine-like inflatable arm to drive the tip of the arm rod to turn outwards, characterized by the elongation of the inflatable arm. After reaching the desired length, stop pressurizing;

[0019] Step 2: Adjust the air pressure in several variable-stiffness airbags;

[0020] When the pressure difference is close to the air pressure in the main cavity, the layer group is squeezed to the greatest extent, and the stiffness of the inflatable arm at the variable stiffness airbag is increased;

[0021] When the pressure difference is close to 0, there is almost no friction between layers, and the stiffness of the inflatable arm at the variable stiffness airbag is the lowest, turning into a steering joint.

[0022] Step 3, contract the rope through the motor-rope device to generate wrinkles at the airbag with the lowest stiffness, realizing the steering control of the inflatable arm.

[0023] Furthermore, in Step 2, the air pressure of the airbag is regulated through a pneumatic circuit;

[0024] The pneumatic circuit includes a main cavity proportional valve for regulating the air pressure in the main cavity, a pressure sensor for detecting the air pressure in the main cavity, a gas source for the inflatable arm system, an electromagnetic proportional valve for regulating the air pressure condition of the variable stiffness airbag, an electromagnetic directional valve for switching the gas path direction, a pressure sensor for detecting the air pressure in the variable stiffness airbag, and a vacuum generator for evacuating the variable stiffness airbag to increase the pressure difference;

[0025] When the stiffness of the arm needs to be increased, switch the electromagnetic directional valve to the circuit where the vacuum generator is located, regulate the electromagnetic proportional valve, increase the air pressure in this circuit, and the gas flowing through the vacuum generator will generate a considerable vacuum degree in the variable stiffness airbag. At this time, the pressure difference in the airbag is the maximum value, and the stiffness of the arm is the largest;

[0026] When the stiffness of the arm needs to be decreased, switch the electromagnetic directional valve to the circuit where the pressure sensor for detecting the air pressure in the variable stiffness airbag is located, regulate the electromagnetic proportional valve, and make the air pressure in this circuit close to the air pressure indicated by the pressure sensor for detecting the air pressure in the main cavity. At this time, the pressure difference in the airbag is the minimum value, and the stiffness of the arm is the smallest.

[0027] A position control method for a variable stiffness method of a vine-like inflatable arm:

[0028] The method specifically includes the following steps:

[0029] Step 1, based on the end trajectory tracking task, adopt a sequential control algorithm to activate and control each joint one by one;

[0030] Step 2, perform closed-loop control on each activated joint; judge the adaptive accuracy, error improvement, and control duration limit in real time;

[0031] Step 3, when any of the judgment conditions in Step 2 is satisfied, switch to the control of the next joint until the end trajectory tracking is completed.

[0032] Furthermore, specifically in Step 2,

[0033] Adaptive precision judgment condition: Determine whether the current control has reached the precision threshold according to the end position error;

[0034] Error improvement judgment condition: Use the reduction of the error between consecutive samplings to determine whether the end of the inflatable arm is approaching the target, that is, whether it is converging;

[0035] Control duration limit condition: If the single-joint control time exceeds the specified time, the current stage is forced to terminate, and after entering the next stage, the subsequent joints continue to complete the residual error compensation.

[0036] An electronic device includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the above method are implemented.

[0037] A computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the steps of the above method are implemented.

[0038] Advantages of the present invention

[0039] The hybrid variable stiffness method mentioned in the present invention can effectively reduce the thickness of the used layer group, reduce the adverse effect of the layer group thickness factor on the tip folding movement of the vine-like inflatable manipulator in the compliant state, and improve the movement performance of the inflatable arm in the telescopic state. Introducing the sandpaper layer can increase the friction between the layer groups, enabling the layer groups to exhibit a larger variable stiffness range, significantly improving the load capacity and anti-interference ability of the inflatable arm rod, and providing sufficient hardware support for the robustness in the control process. The method of leaving an air chamber for the layer group by heat-sealing the arm rod material to fix the position of the layer group can also make the layer group exhibit a lower stiffness in the uncompressed state (the compliant state of the vine-like inflatable arm), which can have an important positive effect on the tip movement of the inflatable arm rod. The above-mentioned hardware-level design can enable the inflatable manipulator to have a larger variable stiffness range, thereby obtaining a larger working space and better movement efficiency.

[0040] The sequential control algorithm in the present invention provides a solution for multi-joint parallel collaborative control of a pneumatic manipulator with few degrees of freedom and multiple actuators. This algorithm can accurately describe the end trajectory of the inflatable arm in space. The three introduced judgment mechanisms in the algorithm can fully improve the control efficiency and avoid the problem of failure to jump out of the single-joint controller loop due to non-converging errors. By setting the duration limit condition, the time for the inflatable manipulator to reach the desired position can be limited within a controllable range. Combining the adaptive precision judgment condition and the error improvement judgment condition can achieve a delicate balance between the control duration and the end trajectory error. The offline trajectory optimization module provides a certain reference for the target values of each stage. Combining this offline module can also make the setting of the threshold and duration more reasonable. Description of the drawings

[0041] Figure 1 It is the growth principle diagram of the vine-like inflatable manipulator; where 1-1 is the sealed base, 1-2 is the inflatable arm, and 1-3 is the recovery spool;

[0042] Figure 2 It is the description of the initial state of the variable stiffness airbag on the vine-like inflatable manipulator; where 2-1 is the airbag, 2-2 is the multi-layer structure layer group, and 2-3 is the main cavity;

[0043] Figure 3 It is the description of the working state of the variable stiffness airbag on the vine-like inflatable manipulator;

[0044] Figure 4 It is the schematic diagram of the arm rod being driven to bend when the variable stiffness airbag is in the working state;

[0045] Figure 5 It is the radial sectional view of the vine-like inflatable manipulator; where 5-1 is the arm rod material and 5-2 is the rope;

[0046] Figure 6 It is the schematic diagram of the pneumatic circuit of the vine-like inflatable manipulator; where 6-1 is the proportional valve for regulating the air pressure in the main cavity (main cavity proportional valve), 6-2 is the pressure sensor for detecting the air pressure in the main cavity, 6-3 is the air source of the inflatable arm system, 6-4 is the electromagnetic proportional valve for regulating the air pressure of the variable stiffness airbag, 6-5 is the electromagnetic directional valve, 6-6 is the pressure sensor for detecting the air pressure in the variable stiffness airbag, and 6-7 is the vacuum generator;

[0047] Figure 7 It is the state change diagram between the blocked state and the unblocked state of the layer group;

[0048] Figure 8 It is the manufacturing process diagram of two joints in the inflatable arm rod; where 8-1 is the inner wall material of the inflatable arm, 8-2 is the outer wall material of the inflatable arm, 8-3 is the heat-sealed gap between the two layer groups, 8-4 is the heat-sealed line, 8-5 is the mixed material layer group, and 8-6 is the same material layer group;

[0049] Figure 9 It is the sectional view of the vine-like inflatable manipulator; where 9-1 is the air pipe arranged on the inner wall material of the inflatable arm, and 9-2 is the stop pin for fixing the rope 5-2;

[0050] Figure 10 It is the control block diagram of the joint controller;

[0051] Figure 11 It is the joint angle obtained by simulating a certain inflatable arm after introducing the offline trajectory optimization module;

[0052] Figure 12 It is the position sequence control flow chart of the inflatable manipulator. Detailed implementation manners

[0053] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0054] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used, unless otherwise specified, are all conventional materials, reagents, methods and instruments in the art, and those skilled in the art can obtain them through commercial channels.

[0055] Embodiment: A variable stiffness method mounted on a vine-like inflatable manipulator. This variable stiffness method is an improvement based on the layer blocking method, hereinafter referred to as the hybrid variable stiffness method. The implementation of the hybrid variable stiffness method requires a hybrid material layer group 8-5, a same material layer group 8-6, an inflatable arm outer wall material 8-2, and an inflatable arm inner wall material 8-1.

[0056] Among them, the hybrid material layer group 8-5 is composed of materials with different friction coefficients stacked together. The inside is two layers of relatively rough P8000 sandpaper, and the outside is two pieces of pure wood pulp standard printing paper with relatively small friction coefficients. The layer group shows anisotropic differences macroscopically; the same material layer group 8-6 is composed of pure wood pulp standard printing paper, and its thickness is slightly larger than that of the hybrid material layer group. The layer group contains eight thin layers.

[0057] The inflatable arm is axially divided into several annular variable stiffness airbags 2-1. Each variable stiffness airbag 2-1 consists of three parts: an inflatable arm outer wall material 8-2, an inflatable arm inner wall material 8-1, and a layer group between the outer wall material and the inner wall material.

[0058] The inflatable arm outer wall material 8-2 is in contact with the outside world, and the inflatable arm inner wall material 8-1 constitutes part of the main cavity 2-3 of the inflatable arm. Both the inflatable arm inner wall material 8-1 and the inflatable arm outer wall material 8-2 are 210D TPU-coated nylon cloth. There are several layer groups in each variable stiffness airbag 2-1. The hybrid material layer group 8-5 and the same material layer group 8-6 are arranged alternately in the circumferential direction, and there is a gap 8-3 between adjacent layer groups.

[0059] To avoid unnecessary buckling, the stiffness of each part of the inflatable arm should be approximately uniform. Therefore, the layer group is designed as a parallelogram structure. The layer group is not fixed in the airbag 2-1 by means of tape or glue, etc. The layers are only lapped together. In the present invention, a gas chamber is left for the layer group by heat-sealing nylon cloth material so that the layer group will not move extensively in the airbag, achieving the purpose of position fixation.

[0060] The implementation steps of the hybrid variable stiffness method are as follows:

[0061] Step 1: Pressurize the main cavity 2-3 of the vine-like inflatable manipulator to drive the tip of the arm rod to turn outwards, characterized by the elongation of the inflatable arm 1-2. After it elongates to the desired length, stop pressurizing.

[0062] Step 2: Adjust the air pressure in several variable stiffness airbags 2-1. When the pressure difference is close to the air pressure in the main cavity 2-3, the layer group is squeezed to the greatest extent, and the friction effect is obvious, and the stiffness of the inflatable arm at this variable stiffness airbag is increased; when the pressure difference is close to 0, there is almost no friction between layers, and the stiffness of the inflatable arm at this variable stiffness airbag is the lowest, almost in a compliant state, and wrinkles are likely to occur here and turn into steering joints.

[0063] The above-mentioned vine-like inflatable manipulator can be driven by three groups of motor-rope devices evenly arranged circumferentially at 120° to achieve motion in three-dimensional space. Among them, the motor is at the root of the arm rod, and the rope 5-2 extends from the root to the tip of the arm rod. When the rope shrinks, wrinkles will occur at the position where the stiffness of the inflatable arm surface is the lowest, manifested as the turning of the arm rod.

[0064] To ensure the effective control of the tip position of the inflatable arm 1-2, only one joint, that is, one variable stiffness airbag 2-1, can be in the lowest stiffness state each time the rope shrinks, thereby realizing the certainty of the turning area and facilitating the kinematic and dynamic solution processes.

[0065] In actual working conditions, operating only one joint is not enough to support the inflatable arm 1-2 to complete complex end trajectory tracking tasks. Therefore, the present invention proposes a sequential control algorithm based on task decomposition.

[0066] This algorithm aims at end trajectory tracking, activates only one joint each time, and performs real-time control through a closed-loop joint controller. After the new end position adjustment generated by the movement of the activated joint is completed, it enters the control link of the next joint until the overall trajectory is completed, that is, each joint advances the end a certain distance in the target direction and hands it over to the next joint to continue to complete the remaining error compensation. This control scheme takes into account both the global target guidance and the convergence of the local stage. This progressive sequential control algorithm can form a control chain that activates joints one by one from the root of the arm rod to the tip of the arm rod and gradually approaches the target, but there may be a problem that "the error cannot converge" during the single-joint control process and it cannot jump out of the current loop, resulting in the inability to execute the subsequent joint control process.

[0067] To optimize the above algorithm, the present invention introduces three judgment mechanisms in each control stage:

[0068] (1) Adaptive accuracy judgment condition

[0069] The end position error can be expressed as follows:

[0070] e = ||x ref - x m || < ε i

[0071] where e is the error value of the end position of the arm; x ref is the expected end position; x m is the actual end position; ε i is the set threshold value.

[0072] If the end position error satisfies the above formula, it indicates that the current control has reached the precision threshold and enters the control stage of the next joint. The joints near the base of the inflatable arm are responsible for large-scale position advancement. It is reasonable to have a large error during this movement process, while the end joints are responsible for fine-tuning actions and have higher requirements for precision. Therefore, the precision required in each stage should be more hierarchical. For this reason, this paper designs an adaptive precision threshold scheme as follows:

[0073]

[0074] where N is the number of joints, that is, the number of variable stiffness airbags; i is the number of the joint controlled in the current stage, and ε max is the set maximum threshold value.

[0075] (2) Error improvement judgment condition

[0076] Use the reduction amount of the error between continuous samplings to judge whether the end of the inflatable arm is approaching the target, that is, whether it converges, as follows:

[0077] ||e k-1 || - ||e k || > δ min

[0078] where e k-1 is the error of the previous step; e k is the error of this time; δ min is the error reduction amount threshold value.

[0079] Satisfying the above situation is judged as the current control being effective, and the control loop of the current joint continues to be executed. Otherwise, it is considered that the control tends to stagnate, and further judgment is made on whether to terminate in advance.

[0080] (3) Control duration limit condition

[0081] To avoid a certain joint getting stuck in control stagnation or response saturation due to the error being difficult to significantly reduce during the control process, a limit value needs to be set for the control duration of each joint. The single-joint control time exceeds Tmax The current stage is then forcibly terminated, and after entering the next stage, the subsequent joints continue to complete the residual error compensation.

[0082] To improve the response efficiency and convergence of the sequential control algorithm, an offline trajectory optimization module can be introduced before real-time control to provide references for the target positions of each stage and the angles of each joint, thereby reducing the overall search space of the control process. By equivalenting each joint of the inflatable arm to a gimbal with two degrees of freedom, the end motion trajectory can be obtained through simulation, and the thresholds and control durations in the judgment basis can be set accordingly.

[0083] This control algorithm takes into account both offline feasibility guidance and online local convergence criteria, has good scalability and robustness, and is applicable to the inflatable arm system with series structure and parallel drive.

[0084] See Figures 1 to 9 This embodiment describes a variable stiffness method for a vine-like inflatable arm.

[0085] As Figure 1 shown, the vine-like inflatable arm mainly includes three parts: 1-1 a sealed base, 1-2 an inflatable arm, and 1-3 a recovery spool. In the initial stage, the arm rod material of the 1-2 inflatable arm is wound around the 1-3 recovery spool, similar to an inside-out sleeve, but the cuff is in a closed state. When the air pressure in the 1-1 sealed base increases, the material of the 1-2 inflatable arm will turn outwards, showing tip growth, and the inflatable arm will elongate.

[0086] As Figure 2 shown, the 1-2 inflatable arm is composed of multiple annular variable stiffness airbags 2-1. There is a thin multi-layer structure group 2-2 inside the 2-1, and the area surrounded by the annular variable stiffness airbags is called the main cavity 2-3. In the initial state, the pressure in the variable stiffness airbag is equal to the pressure in the main cavity (the pressure in the sealed base), that is, the pressure difference in the variable stiffness airbag is close to 0. At this time, the multi-layer structure in the layer group 2-2 is in a relatively loose state, and the vine-like inflatable arm is in a compliant state.

[0087] As Figure 3 shown, when the pressure difference ΔP in the variable stiffness airbag is increased, the multi-layer structure will be squeezed together due to the pressure difference, the normal pressure between layers will increase, and when disturbed, it will show a greater frictional effect outward, showing an increase in the local stiffness of the inflatable arm. In the specific embodiment, the pressure difference ΔP in the variable stiffness airbag can be increased by evacuating the variable stiffness airbag and increasing the air pressure in the main cavity.

[0088] As Figure 4 and Figure 5As shown, when the pressure difference in a variable stiffness airbag is 0 while the pressure differences in the other variable stiffness airbags are relatively large, this variable stiffness airbag becomes a steering joint, applying a tensile force to the cable 5-2 arranged on the surface of the arm rod. A fold will be generated at the position where the stiffness of the arm rod is the smallest, that is, at this variable stiffness airbag, thereby achieving steering. During steering, the variable stiffness airbags at the non-everted arm rod material 5-1 are all in a state where the pressure difference is 0.

[0089] Figure 6 The pneumatic circuit of the vine-like inflatable manipulator is shown. Among them, 6-1 is a proportional valve (main cavity proportional valve) for regulating the air pressure in the main cavity, 6-2 is a pressure sensor for detecting the air pressure in the main cavity, 6-3 is the air source of the inflatable arm system, including equipment such as an air pump and a filter pressure reducing valve, 6-4 is an electromagnetic proportional valve for regulating the air pressure condition of the variable stiffness airbag, 6-5 is an electromagnetic reversing valve, 6-6 is a pressure sensor for detecting the air pressure in the variable stiffness airbag, and 6-7 is a vacuum generator. 6-1 and 6-2 are responsible for adjusting the air pressure in the main cavity to a reasonable value. When the stiffness of the arm rod needs to be increased, the 6-5 electromagnetic reversing valve is switched to the circuit of the 6-7 vacuum generator, and 6-4 is regulated to increase the air pressure in this circuit. The gas flowing through 6-7 will generate a considerable vacuum degree in the variable stiffness airbag. At this time, the pressure difference in the airbag is the maximum value, and the stiffness of the arm rod is the largest; when the stiffness of the arm rod needs to be reduced, the 6-5 electromagnetic reversing valve is switched to the circuit of the 6-6 pressure sensor, and 6-4 is regulated to make the air pressure in this circuit close to the air pressure shown on the 6-2 meter. At this time, the pressure difference in the airbag is the minimum value, and the stiffness of the arm rod is the smallest.

[0090] From Figure 7 the mechanical model between the blocked state and the unblocked state of the multi-layer structure can be deduced. For the convenience of deduction, it is assumed that the multi-layer structure is on a three-point test platform. Since the thickness of the layer group is very small compared to the length and width, the deformation can be regarded as occurring in a two-dimensional plane. The relationship between the deformation amount w of the layer group and the force F applied to it can be expressed as:

[0091]

[0092] In the formula, E is the Young's modulus of the layer group material, L is the length of the layer group, and I is the moment of inertia of the layer group. E and L do not change. Therefore, when the layer group has the same deformation amount w, the force F (perturbed) applied to the layer group is proportional to the moment of inertia I of the layer group. That is, the larger the moment of inertia of the layer group, the stronger the anti-disturbance ability.

[0093] In the blocked state, the state between layers is called the "pre-slip" state. The axial shear stress at the interface of the layers remains at a critical state, lower than the static friction threshold (μP). In this case, all layers are still in a "bonded" state, and there is no relative sliding between them. The interface is in a state controlled by static friction, and the overall structure shows a relatively high overall stiffness, and the mechanical response is similar to that of a complete whole. In the unblocked state, there is a very high probability of relative slip between layers. The state where all layers may slip is called the "full-slip" state. There is no effective bonding between layers, and the overall stiffness of the structure decreases significantly, showing mechanical characteristics of stronger flexibility and weaker load-bearing capacity. Between the two, there is a partial-slip stage. There are two types of structures between the layer groups. The layers in the middle area slip, and their longitudinal shear stress is equal to the maximum allowable shear stress, while the upper and lower areas are similar to the characteristics of the layer groups in the pre-slip stage. The overall structure shows a composite characteristic that includes both bonding behavior and slip behavior, and the stiffness is lower than that in the pre-slip stage. The moment of inertia of the layer groups in the "pre-slip" state and the "full-slip" state can be expressed as shown in the following equations:

[0094]

[0095] In the equations, b is the width of the layer group, t is the thickness of the layer group, and n is the number of layers in the layer group. It can be seen that in the "pre-slip" state, the layer group has the strongest anti-interference ability and the largest stiffness; in the "full-slip" state, the layer group has the weakest anti-interference ability and the smallest stiffness. In occasions where the inflatable arm needs to be flexible, such as during tip growth and tip retraction, the layers need to be in a relatively loose state; in occasions where the inflatable arm needs to exhibit high stiffness, such as during shape locking and performing interactive tasks, the layers need to fit closely together.

[0096] As Figure 8 shown, 8-1 is the inner wall material of the inflatable arm, 8-2 is the outer wall material of the inflatable arm. There are layer groups of 8-5 mixed materials and layer groups of 8-6 same materials between the two. To facilitate the gas flow within the same variable stiffness airbag, a heat-sealed gap 8-3 between the two layer groups is designed, and 8-4 is the heat-sealing line. 8-5 and 8-6 are arranged alternately to ensure the consistency of the arm stiffness. To ensure that the layer group is in the full-slip state during tip movement, the method of fixing the layer group with tape and double-sided tape is abandoned. The layer group is directly placed on the arm material, and the heat-sealing fixing method is used to lock the movement range of the layer group within a very small area. The specific manufacturing steps are as follows:

[0097] Step 1: Cut out two pieces of arm materials 8-1 and 8-2 with appropriate sizes;

[0098] Step 2: Draw heat-sealing lines on the inner wall material and place the prepared layer groups 8-5 and 8-6 on the arm rod material;

[0099] Step 3: Lay the outer wall material on the inner wall material to form a "sandwich" structure of outer wall material - layer group - inner wall material;

[0100] Step 4: Perform heat-sealing along the heat-sealing lines to lock the movement range of the layer group;

[0101] Step 5: Roll up the arm rod material along the long side and fix it, and the arm rod is manufactured.

[0102] Figure 9 Figure 9-1 shows a more complete imitation vine inflatable arm structure. The air pipe 9-1 is arranged on the inner wall material of the inflatable arm. Appropriate-sized air pipe openings are made on the surface of the arm rod material, and the air pipe can be pasted at the air pipe openings. The stop pin 9-2 for fixing the rope 5-2 can be pasted on the outer wall surface of the inflatable arm with double-sided tape or the like.

[0103] See Figures 10 to 12 This embodiment describes a position control algorithm for an imitation vine inflatable arm according to this embodiment.

[0104] When the imitation vine inflatable arm in the state of few actuators - multiple degrees of freedom performs end trajectory tracking, joints need to be specified. The present invention first designs a joint controller as shown in Figure 10 , and then extends the joint controller to the entire arm using the sequential control algorithm.

[0105] The present invention introduces a method for establishing a joint controller. The controller is based on the error e between the current actual state and the desired state of the system, dynamically generates a control input signal u, and the generalized coordinates, that is, two quantities (the steering angle ψ and the bending angle θ of the inflatable arm) in the joint space, can be obtained through forward dynamics. The generalized coordinate ξ is further transmitted back into the controller. To further improve the robustness and anti-interference ability of the system, a gravity compensation term G(ξ) is introduced into the control law. This term is used to actively offset the system deviation caused by external environmental factors such as gravity and air disturbance, thereby enhancing the stability and tracking ability of the controller. The control law can be expressed as shown in Equation (5-5):

[0106]

[0107] In the formula, e represents the end position error, e = x ref -x m ; represents the corresponding end velocity error; K represents the gain, K p is the proportional gain, K d is the differential gain, and the symmetric positive definite matrix G(ξ) is the gravity term; Jp J(ξ) is the Jacobian matrix of the end - effector position with respect to the joint - space variables; J q J(ξ) is the Jacobian matrix that maps the generalized forces to the drive space.

[0108] The basis of this controller is a PD (Proportional - Derivative) controller with a gravity - compensation term. The actual end - effector position x is obtained through an external sensing device m , and the end - effector velocity is obtained by differentiating the actual position and then passing through a low - pass filter to eliminate high - frequency noise. These two types of data are fed back to the upper computer in real - time. The filter can adopt the following recursive form:

[0109]

[0110] where k represents the current time step (the k - th sampling); represents the original velocity estimate at the current time step k, which comes from the difference value; is the filtering result at the previous time step; is the filtering output at the current time step, that is, the new velocity value; α is the filter coefficient, and α ∈ (0, 1).

[0111] Before performing the Figure 12 shown control program, introducing offline trajectory optimization to carry out preliminary trajectory - tracking simulation experiments can improve the control accuracy and control efficiency. The present invention introduces an offline trajectory - optimization method for an inflatable arm with eight variable - stiffness airbags (eight joints). Based on the tools in the MATLAB Robotics Toolbox, the reachability analysis of each joint combination is carried out. The minimum end - effector error point is obtained through fmincon optimization, and then a feasible trajectory is obtained by using jtraj() interpolation, so as to provide a reference for the target positions in each stage and reduce the overall search space. Based on the characteristics of the generalized coordinates in the simulation environment, each joint of the inflatable arm can be equivalent to a gimbal with two degrees of freedom, and the angle change is as Figure 11 shown.

[0112] Figure 12It shows the specific process of a sequential control algorithm based on error threshold judgment. External sensors such as depth cameras can be used to sense the initial position of the end of the vine-like inflatable arm. After position calculation, the error between the end of the vine-like inflatable arm and the target position can be obtained. In each stage, only the control sub-process of the i-th joint is activated, and the steering angle and bending angle of this joint are adjusted to the desired position. During the control process, the system will continuously judge whether the end position error meets the preset precision threshold. If it meets, it is considered that the current joint reaches the target state and enters the control process of the next joint i+1. Otherwise, it will further judge whether the convergence condition is met or whether the maximum control time is exceeded. If the error does not meet the precision requirement but is still within the acceptable convergence interval, the system will continue to execute the closed-loop control of the current joint until the error converges; if the target position is not reached after the control times out, the current stage control will be terminated and the next stage will be entered according to the strategy.

[0113] Through this sequential control strategy, the staged drive control of the multi-segment structure of the inflatable arm is realized, effectively reducing the coupling interference between joints and improving the stability and trajectory tracking accuracy of the system.

[0114] An electronic device includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the above method are implemented.

[0115] A computer-readable storage medium is used to store computer instructions, and when the computer instructions are executed by a processor, the steps of the above method are implemented.

[0116] The memory in the embodiments of the present application may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. Among them, the non-volatile memory may be a read only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache. By way of example but not limitation, many forms of RAM are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchlink DRAM (SLDRAM), and direct rambus RAM (DR RAM). It should be noted that the memory of the method described in the present invention is intended to include but not limited to these and any other suitable types of memories.

[0117] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer instructions are loaded and executed on a computer, the processes or functions described in the embodiments of the present application are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired means such as coaxial cables, optical fibers, digital subscriber line (DSL), or wireless means such as infrared, wireless, microwave, etc. The computer-readable storage medium can be any available medium that the computer can access or a data storage device such as a server, data center, etc. that contains one or more integrated available media. The available media can be magnetic media such as floppy disks, hard disks, magnetic tapes, optical media such as high-density digital video discs (DVDs), or semiconductor media such as solid state discs (SSDs), etc.

[0118] In the implementation process, the steps of the above method can be completed by the integrated logic circuit of the hardware in the processor or the instructions in the form of software. The steps of the method disclosed in the embodiments of the present application can be directly embodied as being executed by the hardware processor or completed by the combination of the hardware and software modules in the processor. The software module can be located in a mature storage medium in the art such as random access memory, flash memory, read-only memory, programmable read-only memory, or electrically erasable programmable memory, registers, etc. This storage medium is located in the memory, and the processor reads the information in the memory and combines its hardware to complete the steps of the above method. To avoid repetition, it will not be described in detail here.

[0119] It should be noted that the processor in the embodiments of this application can be an integrated circuit chip with signal processing capabilities. During implementation, the steps of the above method embodiments can be completed by the integrated logic circuit in the hardware of the processor or instructions in software form. The above-mentioned processor can be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components. It can implement or execute the various methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The steps of the method disclosed in combination with the embodiments of this application can be directly embodied as being executed and completed by a hardware decoding processor, or executed and completed by a combination of hardware and software modules in the decoding processor. The software module can be located in a mature storage medium in the art such as random access memory, flash memory, read-only memory, programmable read-only memory, or electrically erasable programmable memory, registers, etc. This storage medium is located in the memory, and the processor reads the information in the memory and combines its hardware to complete the steps of the above method.

[0120] The above has introduced in detail a variable stiffness method and its position control method for an imitation vine inflatable arm proposed by the present invention, and has elaborated on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An inflatable vine-like arm, characterized in that: The inflatable vine-like arm includes a sealed base (1-1), an inflatable arm (1-2) and a recovery spool (1-3); In the initial stage, the arm rod material of the inflatable arm (1-2) is wound around the recovery spool (1-3). When the air pressure in the sealed base (1-1) rises, the material of the inflatable arm (1-2) will turn outwards, showing tip growth, and the inflatable arm elongates; The inflatable arm (1-2) is composed of a plurality of annular variable-stiffness airbags (2-1) distributed axially. Each annular variable-stiffness airbag (2-1) includes an inner wall material (8-1) of the inflatable arm, an outer wall material (8-2) of the inflatable arm that is wrapped outside the inner wall material (8-1) and contacts the outside, and a thin-layer multi-layer structure layer group (2-2) located between the outer wall material (8-2) and the inner wall material (8-1) of the inflatable arm; The main cavity (2-3) area of the inflatable arm (1-2) is formed by the inner wall material (8-1) of the inflatable arm; The multi-layer structure layer group (2-2) includes a mixed material layer group (8-5) and a same material layer group (8-6), which are arranged alternately along the circumferential direction, and there are gaps (8-3) between adjacent layer groups; The annular variable-stiffness airbag (2-1) adjusts the friction state between layer groups by adjusting the internal pressure difference, realizing the adjustable control of the local stiffness of the inflatable vine-like arm.

2. The inflatable vine-like arm according to claim 1, characterized in that: The mixed material layer group (8-5) is formed by superimposing materials with different friction coefficients, with two rough material layers inside and a low-friction material layer outside; The same material layer group (8-6) is formed by superimposing a plurality of thin layers of the same material.

3. The inflatable vine-like arm according to claim 2, characterized in that: The multi-layer structure layer group (2-2) is designed as a parallelogram structure; it is fixed between the inner wall material (8-1) and the outer wall material (8-2) of the inflatable arm by a heat-sealing line (8-4), and the layers overlap each other to form an air chamber to prevent the layer group from moving.

4. The inflatable vine-like arm according to claim 3, characterized in that: The inflatable vine-like arm further includes three motor-rope devices evenly arranged at 120° along the circumferential direction, where the motor is at the root of the arm rod, and the rope (5-2) extends from the root to the tip of the arm rod; When the pressure difference of a certain variable-stiffness airbag (2-1) approaches zero, a steering joint is formed at this place, and wrinkles are generated at the lowest stiffness by contracting the rope (5-2) to drive the inflatable arm to bend.

5. A variable-stiffness method for an inflatable vine-like arm according to any one of claims 1 to 4, characterized in that: The variable-stiffness method includes the following steps: Step 1: Pressurize the main cavity (2-3) of the inflatable vine-like arm to drive the tip of the arm rod to turn outwards, characterized by the elongation of the inflatable arm (1-2). Stop pressurizing after reaching the desired length; Step 2: Adjust the air pressure in several variable-stiffness airbags (2-1); When the pressure difference is close to the air pressure in the main cavity (2-3), the layer group is squeezed to the greatest extent, and the stiffness of the inflatable arm at this variable-stiffness airbag is increased; When the pressure difference is close to 0, there is almost no friction between layers, and the stiffness of the inflatable arm at the variable stiffness airbag is the lowest, transforming into a steering joint; Step 3, contract the rope (5-2) through the motor-rope device to generate wrinkles at the airbag (2-1) with the lowest stiffness, realizing the steering control of the inflatable arm.

6. The variable stiffness method according to claim 5, characterized in that: In step 2, the air pressure of the airbag (2-1) is adjusted through a pneumatic circuit; The pneumatic circuit includes a main cavity proportional valve (6-1) for regulating the air pressure in the main cavity, a pressure sensor (6-2) for detecting the air pressure in the main cavity, a gas source (6-3) of the inflatable arm system, an electromagnetic proportional valve (6-4) for regulating the air pressure condition of the variable stiffness airbag, an electromagnetic reversing valve (6-5) for switching the air path direction, a pressure sensor (6-6) for detecting the air pressure in the variable stiffness airbag, and a vacuum generator (6-7) for evacuating the variable stiffness airbag to increase the pressure difference; When the stiffness of the arm needs to be increased, reverse the electromagnetic reversing valve (6-5) to the circuit where the vacuum generator (6-7) is located, regulate the electromagnetic proportional valve (6-4), increase the air pressure in this circuit, and the gas flowing through the vacuum generator (6-7) will create a considerable vacuum degree in the variable stiffness airbag (2-1). At this time, the pressure difference in the airbag is the maximum value, and the stiffness of the arm is the largest; When the stiffness of the arm needs to be decreased, reverse the electromagnetic reversing valve (6-5) to the circuit where the pressure sensor (6-6) for detecting the air pressure in the variable stiffness airbag is located, regulate the electromagnetic proportional valve (6-4), and make the air pressure in this circuit close to the air pressure shown by the pressure sensor (6-2) for detecting the air pressure in the main cavity. At this time, the pressure difference in the airbag is the minimum value, and the stiffness of the arm is the smallest.

7. A position control method based on the variable stiffness method of the vine-like inflatable arm according to claim 5 or 6, characterized in that: The method specifically includes the following steps: Step 1, based on the end trajectory tracking task, adopt a sequential control algorithm to activate and control each joint one by one; Step 2, perform closed-loop control on each activated joint; judge the adaptive accuracy, error improvement, and control duration limit in real time; Step 3, when any of the judgment conditions in step 2 is met, switch to the control of the next joint until the end trajectory tracking is completed.

8. The position control method according to claim 7, wherein: Specifically in step 2, Adaptive accuracy judgment condition: Judge whether the current control has reached the accuracy threshold according to the end position error; Error improvement judgment condition: Use the reduction amount of the error between continuous samplings to judge whether the end of the inflatable arm is approaching the target, that is, whether it is converging; Control duration limit condition: If the single-joint control time exceeds the specified time, forcefully terminate the current stage, and after entering the next stage, the subsequent joints will continue to complete the residual error compensation.

9. An electronic device, comprising a memory and a processor, the memory storing a computer program, characterized in that, The processor implements the steps of the method described in claim 7 or 8 when executing the computer program.

10. A computer-readable storage medium for storing computer instructions, characterized in that, The computer instructions implement the steps of the method described in claim 7 or 8 when executed by the processor.

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