Rigidity-variable method of rattan-like inflatable arm and position control method thereof

Abstract

The application provides a variable stiffness method of a vine-like inflatable arm and a position control method thereof, and belongs to the technical field of soft robots. The inflatable arm realizes the tip eversion to be elongated to a desired length through the air pressure effect, the pressure difference in the annular variable stiffness air bag around the arm rod is adjusted to control the local stiffness of the inflatable arm, the wrinkle is generated at the position with the lowest stiffness in combination with a motor-rope device, and the steering control of the inflatable arm is realized; when the position control is performed, sequential control algorithm is adopted to sequentially perform closed loop control on each joint based on the end trajectory tracking task, and three kinds of criteria are established in the algorithm to help the end trajectory tracking task to be completed. The variable stiffness range of the vine-like inflatable mechanical arm is improved, a new manufacturing process is adopted, the level of tip movement is improved, and the sequential control algorithm can help the inflatable arm to realize precise multi-joint parallel collaborative control.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of soft robots, and particularly relates to a variable stiffness method of a vine-like inflatable arm and a position control method thereof. BACKGROUND

[0002] As an important branch of soft robots, the vine-like inflatable arm has the structural characteristics of continuous compliance, can be elongated by turning the tip material outward, and can be retracted by turning the tip material inward. The vine-like inflatable arm has nearly infinite degrees of freedom in geometry, but the actual controllable degrees of freedom are limited. Adding drivers according to the number of degrees of freedom will make the entire system too complex and large. How to control more degrees of freedom with as few drivers as possible is one of the problems that must be solved in the field of inflatable arms. The variable stiffness method can dynamically adjust the stiffness of the entire or local vine-like inflatable arm, so that any area on the arm surface becomes a turning part, and the remaining areas remain shape-locked. Combined with the parallel arrangement of the driver, the shape control process of the vine-like inflatable arm can be realized. The existing variable stiffness method mostly needs to introduce a rigid structure, which is not conducive to the tip movement process of the vine-like inflatable arm in a compliant state, and the variable stiffness range also has room for improvement. Reducing the adverse effects of the variable stiffness method on the movement of the inflatable arm and improving the variable stiffness range are of great significance to the control performance of the vine-like inflatable arm.

[0003] The vine-like inflatable arm structure with fewer drivers and more degrees of freedom cannot achieve multi-joint parallel collaborative control. To ensure control accuracy, detailed control steps of the vine-like inflatable arm are needed to achieve accurate kinematics and dynamics solving process. Designing a control algorithm for the vine-like inflatable arm with a variable stiffness method can provide important theoretical support and technical guarantee for the application of the inflatable arm in actual working conditions. SUMMARY

[0004] In summary, the present application aims to design a variable stiffness method to improve the variable stiffness range of the vine-like inflatable arm and reduce the adverse effects of rigid structures on the tip folding movement of the vine-like inflatable arm. Starting from the structural characteristics of the vine-like inflatable arm with fewer drivers and more degrees of freedom, a sequential control algorithm considering multi-joint three-dimensional movement is designed to achieve precise multi-joint parallel collaborative control process. A variable stiffness method and position control method of the vine-like inflatable arm are proposed.

[0005] The present application is implemented by 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 on the recovery spool. When the air pressure in the closed base rises, the material of the inflatable arm will evert, showing tip growth, and the inflatable arm will elongate.

[0008] The inflatable arm is composed of a plurality of annular variable stiffness air bags distributed along the axial direction. Each annular variable stiffness air bag comprises an inflatable arm inner wall material, an inflatable arm outer wall material wrapped outside the inner wall material and in contact with the outside world, and a thin sheet-shaped multi-layer structure layer group between the inflatable arm outer wall material and the inflatable arm inner wall material.

[0009] The main cavity region of the inflatable arm is composed of the inflatable arm inner wall material;

[0010] The multi-layer structure layer group comprises a mixed material layer group and a same material layer group, which are arranged alternately in the circumferential direction and have a gap between adjacent layer groups;

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

[0012] Further, the mixed material layer group is composed of materials with different friction coefficients, and the inside is two layers of rough material, and the outside is a low-friction material layer.

[0013] The same material layer group is composed of multiple thin layers of the same material.

[0014] Further, the multi-layer structure layer group is designed as a parallelogram structure. It is fixed between the inflatable arm inner wall material and the inflatable arm outer wall material by a heat sealing line, and the layers are overlapped together to form an air chamber to prevent the layer group from moving.

[0015] Further, the vine-like inflatable arm further comprises three groups of motor-rope devices arranged uniformly at 120° in the circumferential direction, wherein 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 air bag approaches zero, a turning joint is formed at that place. By contracting the rope, a wrinkle is generated at the place with the lowest stiffness, driving the inflatable arm to bend.

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

[0018] Step 1: pressurize the main cavity of the vine-like inflatable arm, drive the tip of the arm rod to evert, characterized by elongation of the inflatable arm, and stop pressurizing when the elongation reaches the desired length;

[0019] Step 2: adjust the air pressure in a plurality of variable stiffness air bags;

[0020] When the pressure difference is close to the air pressure in the main cavity, the layer group is subjected to the maximum degree of extrusion, and the stiffness of the inflatable arm at the variable stiffness air bag is increased;

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

[0022] Step three, the rope is retracted through the motor-rope device, wrinkles are generated at the air bag with the lowest stiffness, and steering control of the inflatable arm is realized.

[0023] Further, in step two, the air pressure adjustment of the air bag is realized through a pneumatic circuit;

[0024] The pneumatic circuit comprises 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, an air source of the inflatable arm system, an electromagnetic proportional valve for regulating the air pressure of the variable stiffness air bag, an electromagnetic reversing valve for switching the direction of the air circuit, a pressure sensor for detecting the air pressure in the variable stiffness air bag, and a vacuum generator for vacuumizing the variable stiffness air bag to increase the pressure difference;

[0025] When the stiffness of the arm rod needs to be increased, the electromagnetic reversing valve is switched to the circuit where the vacuum generator is located, the electromagnetic proportional valve is regulated, the air pressure of the circuit is increased, and the gas flowing through the vacuum generator will generate a corresponding vacuum degree in the variable stiffness air bag. At this time, the pressure difference in the air bag is the maximum, and the stiffness of the arm rod is the maximum;

[0026] When the stiffness of the arm rod needs to be reduced, the electromagnetic reversing valve is switched to the circuit where the pressure sensor for detecting the air pressure in the variable stiffness air bag is located, the electromagnetic proportional valve is regulated, the air pressure of the circuit is close to the air pressure displayed by the pressure sensor for detecting the air pressure in the main cavity, at this time, the pressure difference in the air bag is the minimum, and the stiffness of the arm rod is the minimum.

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

[0028] The method specifically comprises the following steps:

[0029] Step 1, based on the end trajectory tracking task, a sequential control algorithm is used to activate control joint by joint;

[0030] Step 2, closed-loop control is performed on each activated joint; real-time adaptive accuracy, error improvement and control time limit are judged;

[0031] 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.

[0032] Further, in step 2, specifically,

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

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

[0035] Control duration limit condition: if the single-joint control time exceeds the specified time, the current stage is forcibly terminated, and the next stage is entered to continue the residual error compensation by the subsequent joint.

[0036] An electronic device includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0037] A computer readable storage medium for storing computer instructions, the computer instructions are executed by a processor to implement the steps of the above method.

[0038] Advantages of the present application

[0039] The hybrid variable stiffness method mentioned in the present application can effectively reduce the thickness of the layer group used, reduce the adverse effects of the layer group thickness on the tip folding motion of the inflatable vine-like mechanical arm in the compliant state, and improve the motion performance of the inflatable arm in the extended state. The introduction of the sandpaper layer can increase the friction between the layer groups, making the layer group exhibit a larger variable stiffness range, which can significantly improve the load capacity and anti-interference ability of the inflatable arm rod, and provide sufficient hardware support for the robustness in the control process. The method of leaving air chambers for the layer group by heat-sealing the arm rod material can also make the layer group exhibit lower stiffness in the uncompressed state (compliant state of the inflatable vine-like mechanical arm), which can have an important positive effect on the tip motion of the inflatable arm rod. The above hardware-level design can make the inflatable mechanical arm have a larger variable stiffness range, thereby obtaining a larger working space and better motion efficiency.

[0040] The sequential control algorithm in the present application provides a multi-joint parallel cooperative control solution for the inflatable mechanical arm with few degrees of freedom and multiple drivers. The algorithm can provide accurate end trajectory description for the inflatable arm in space. The three judgment mechanisms introduced in the algorithm can fully improve the control efficiency and avoid the problem of failure to exit the single-joint controller loop due to error convergence. By setting the time limit condition, the time for the inflatable mechanical arm to reach the desired position can be limited within a controllable range. Combined with the adaptive accuracy judgment condition and the error improvement judgment condition, a clever trade-off between control duration and end trajectory error can be achieved. The offline trajectory optimization module provides a certain reference for the target value of each stage, and the setting of the threshold and time can also be more reasonable in combination with the offline module. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

[0044] Figure 4 is the schematic diagram of the arm link bending driven when the variable stiffness air bag is in the working state;

[0045] Figure 5 is the radial section view of the vine-like inflatable manipulator; wherein 5-1 is the arm link material, and 5-2 is the rope;

[0046] Figure 6 is the pneumatic circuit schematic diagram of the vine-like inflatable manipulator; wherein 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 air bag, 6-5 is the electromagnetic reversing valve, 6-6 is the pressure sensor for detecting the air pressure in the variable stiffness air bag, and 6-7 is the vacuum generator;

[0047] Figure 7 is the state change diagram of the layer group from the blocked state to the unblocked state;

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

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

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

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

[0052] Figure 12 is the position sequence control flowchart of the inflatable manipulator. DETAILED DESCRIPTION

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

[0054] The experimental methods used in the following embodiments are conventional methods without special instructions. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art without special instructions, and can be obtained by a person of ordinary skill in the art through commercial channels.

[0055] Embodiment: A variable stiffness method mounted on a rattan-like inflatable mechanical arm, which is improved on the basis of 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] The hybrid material layer group 8-5 is composed of materials with different friction coefficients, 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 coefficient. The layer group shows anisotropic difference in macroscopic view; the same material layer group 8-6 is composed of pure wood pulp standard printing paper, which is slightly thicker than the hybrid material layer group, and contains eight thin layers in the layer group.

[0057] The inflatable arm is divided into a plurality of annular variable stiffness air bags 2-1 along the axial direction, each variable stiffness air bag 2-1 is composed of three parts: the inflatable arm outer wall material 8-2, the inflatable arm inner wall material 8-1 and the 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, and the inflatable arm inner wall material 8-1 constitutes the main cavity 2-3 part of the inflatable arm. The inflatable arm inner wall material 8-1 and the inflatable arm outer wall material 8-2 are both 210D TPU coated nylon cloth, and there are several portions of layer groups in each variable stiffness air bag 2-1. The hybrid material layer group 8-5 and the same material layer group 8-6 are arranged alternately along the circumferential direction, and there is a gap 8-3 between adjacent layer groups.

[0059] In order to avoid unnecessary buckling, the stiffness of the inflatable arm at each part should be approximately uniform, so the layer group is designed as a parallelogram structure. The layer group is not fixed in the air bag 2-1 by using adhesive tape or glue, and the layers are only overlapped together. The present application leaves air chambers for the layer group by heat sealing the nylon cloth material, so that the layer group does not move in a large range in the air bag, achieving the purpose of fixed position.

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

[0061] Step 1: pressurize the main cavity 2-3 of the inflatable vine-like robotic arm, drive the arm rod tip to evert, and characterize the elongation of the inflatable arm 1-2. Stop pressurizing when the desired length is reached.

[0062] Step 2: adjust the air pressure in the variable stiffness air bags 2-1. When the pressure difference approaches the air pressure in the main cavity 2-3, the layers are subjected to the maximum degree of extrusion, and the friction is obvious. The stiffness of the inflatable arm at this variable stiffness air bag is increased. When the pressure difference approaches 0, there is almost no friction between the layers. The stiffness of the inflatable arm at this variable stiffness air bag is the lowest, and it is almost in a compliant state. Wrinkles are easily produced here, and the turning joint is converted.

[0063] The above-mentioned inflatable vine-like robotic arm can be driven by three groups of motor-rope devices arranged uniformly at 120° in the circumferential direction to realize movement in three-dimensional space, wherein 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 is contracted, wrinkles will be produced at the position where the stiffness of the inflatable arm is the lowest, showing the turning of the arm rod.

[0064] To ensure effective control of the position of the tip of the inflatable arm 1-2, only one joint can be contracted at a time, i.e. only one variable stiffness air bag 2-1 is in the lowest stiffness state, thereby realizing the certainty of the turning area and facilitating the solving process of kinematics and dynamics.

[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 application proposes a sequential control algorithm based on task decomposition.

[0066] The algorithm takes end trajectory tracking as the target, activates only one joint at a time, and controls in real time through a closed-loop joint controller. After the activated joint moves and the new end position adjustment is completed, the next joint control link is entered, and the whole trajectory is completed, i.e. each joint pushes the end to the target direction by a certain distance, and the next joint continues 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 each joint from the root of the arm rod to the tip of the arm rod and gradually approaches the target. However, it may produce the problem of "error cannot be converged" in the single joint control process, which cannot jump out of the current cycle, and thus the subsequent joint control process cannot be executed.

[0067] To optimize the above-mentioned algorithm, the present application 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] In the formula, e is the error value of the arm end position; x ref is the end desired position; x m is the end actual position; ε i is the set threshold value.

[0072] If the end position error satisfies the above formula, it means that the current control has reached the precision threshold, and the control stage of the next joint is entered. The joints near the base of the inflatable arm are responsible for large-scale position advancement, and large errors occur in this movement process, which is a reasonable phenomenon. The end joint is responsible for fine-tuning action, and the requirement for precision is higher, so the precision required by each stage should be more hierarchical. For this purpose, an adaptive precision threshold scheme is designed as follows:

[0073]

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

[0075] (2) Error improvement judgment condition

[0076] The reduction of error between consecutive samples is used to judge whether the end of the inflatable arm is approaching the target, i.e. whether it is converging, as follows:

[0077] || e k-1 || - || e k || > δ min

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

[0079] If the above condition is satisfied, it is judged that the current control is effective, and the control loop of the current joint is continued. Otherwise, it is considered that the control tends to be stagnant, and further judgment is made whether to terminate early.

[0080] (3) Control duration limit condition

[0081] To avoid a joint from being trapped in a control stagnation or response saturation state due to difficulty in significantly reducing the error during control, a limit value needs to be set for the control duration of each joint. If the single joint control time exceeds Tmax The current stage is forcibly terminated, and the next stage is entered, and the residual error compensation is continued by the subsequent joint.

[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 reference for the target position of each stage and the angle of each joint, thereby reducing the overall search space of the control process. By equating 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 threshold and control duration in the judgment basis can be set accordingly.

[0083] The control algorithm takes into account both offline feasibility guidance and online local convergence criteria, has good scalability and robustness, and is suitable for inflatable arm systems with serial structure and parallel drive.

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

[0085] As shown in Figure 1 , the vine-like inflatable arm mainly includes a 1-1 closed base, a 1-2 inflatable arm, and a 1-3 recovery spool. In the initial stage, the arm rod material of the 1-2 inflatable arm is wound on the 1-3 recovery spool, similar to an inverted sleeve, but the sleeve opening is in a closed state. When the air pressure in the 1-1 closed base increases, the material of the 1-2 inflatable arm will evert, showing tip growth and elongation of the inflatable arm.

[0086] As shown in Figure 2 , the 1-2 inflatable arm is composed of multiple annular variable stiffness airbags 2-1, and there are thin sheet-shaped multi-layer structure groups 2-2 in 2-1. The area surrounded by the annular variable stiffness airbags is called the main cavity 2-3. In the initial state, the pressure difference in the variable stiffness airbag is close to 0, i.e. the pressure in the variable stiffness airbag is equal to the pressure in the main cavity (the pressure in the closed base), at this time the multi-layer structure in the structure group 2-2 is in a relatively loose state, and the vine-like inflatable arm is in a compliant state.

[0087] As shown in Figure 3 , 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 the layers will increase, and when disturbed, it will exhibit greater frictional effect outward, showing an increase in the local stiffness of the inflatable arm. In specific embodiments, the pressure difference ΔP in the variable stiffness airbag can be increased by vacuumizing the variable stiffness airbag and increasing the air pressure in the main cavity.

[0088] As shown in Figure 4 and Figure 5When the pressure difference in a certain variable stiffness air bag is 0, and the pressure differences in the rest of the variable stiffness air bags are relatively large, the variable stiffness air bag becomes a steering joint, exerts a pulling force on the rope 5-2 arranged on the surface of the arm rod, and wrinkles are generated at the position where the arm rod has the minimum stiffness, i.e., the variable stiffness air bag, thereby achieving steering. During steering, the variable stiffness air bags at the positions of the arm rod material 5-1 that are not everted are all in the state of 0 pressure difference.

[0089] Figure 6 The pneumatic circuit of the rattan-like inflatable mechanical arm is shown, wherein 6-1 is a proportional valve for regulating the air pressure in the main cavity (main cavity proportional valve), 6-2 is a pressure sensor for detecting the air pressure in the main cavity, 6-3 is an air source of the inflatable arm system, including a gas pump and a filtering pressure reducing valve and the like, 6-4 is an electromagnetic proportional valve for regulating the air pressure of the variable stiffness air bag, 6-5 is an electromagnetic reversing valve, 6-6 is a pressure sensor for detecting the air pressure in the variable stiffness air bag, 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 electromagnetic reversing valve 6-5 is reversed to the circuit of the vacuum generator 6-7, the electromagnetic proportional valve 6-4 is regulated, the air pressure of the circuit is increased, and the gas flowing through 6-7 will generate a corresponding vacuum degree in the variable stiffness air bag. At this time, the pressure difference in the air bag is the maximum, and the stiffness of the arm rod is the maximum. When the stiffness of the arm rod needs to be reduced, the electromagnetic reversing valve 6-5 is reversed to the circuit of the pressure sensor 6-6, the electromagnetic proportional valve 6-4 is regulated, the air pressure of the circuit is close to the air pressure displayed by 6-2, and at this time, the pressure difference in the air bag is the minimum, and the stiffness of the arm rod is the minimum.

[0090] By Figure 7 The mechanical model of the multilayer structure between the blocked state and the unblocked state can be derived. For convenience of derivation, it is assumed that the multilayer structure is on a three-point test platform. Since the thickness of the layer group is very small compared with the length and width, the deformation can be regarded as occurring in a two-dimensional plane, and the relationship between the deformation w of the layer group and the force F received by the layer group can be represented as:

[0091]

[0092] In the formula, E is the Young's modulus of the material of the layer group, 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, so in the case of the same deformation w of the layer group, the force F (disturbance) received by 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 disturbance resistance.

[0093] In the blocked state, the state between layers is called "pre-slip" state, the axial shear stress at the interface of the layers remains critical, below the static friction threshold (μP), in this case, all layers are still in the "bonding" state, no relative slip occurs between each other, the interface is in a state controlled by static friction, the overall structure presents a higher overall stiffness, and the mechanical response is similar to a complete whole; in the unblocked state, there is a high probability of relative slip between layers, and all layers have the possibility of slip, which is called "full-slip" state, the layers between each other no longer have effective bonding effect, the overall stiffness of the structure decreases significantly, and presents a stronger flexibility and weaker load capacity. Between the two, there is a partial slip stage, the structure between the layer groups in the middle region slips, and the longitudinal shear stress is equal to the maximum allowable shear stress, while the upper and lower regions have similar characteristics to the pre-slip stage, the overall structure presents a composite characteristic containing both bonding and slip behaviors, and the stiffness is lower than that in the pre-slip stage. The inertia moments of the layer groups in the "pre-slip" state and the "full-slip" state can be represented by the following formulas:

[0094]

[0095] In the formula, 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 anti-interference ability of the layer group is the strongest, and the stiffness is the largest; in the "full-slip" state, the anti-interference ability of the layer group is the weakest, and the stiffness is the smallest. In the case where the inflatable arm needs to be flexible, such as tip growth and tip retraction, the layers need to be in a relatively loose state; in the case where the inflatable arm needs to exhibit high stiffness, such as shape locking and performing interactive tasks, the layers need to be closely attached.

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

[0097] Step one: cut two pieces of arm rod material 8-1 and 8-2 with appropriate size;

[0098] Step two: draw the heat sealing line on the inner wall material, and place the prepared layer group 8-5 and 8-6 on the arm rod material;

[0099] Step three: lay the outer wall material on the inner wall material to form an "sandwich" structure of outer wall material-layer group-inner wall material;

[0100] Step four: heat seal along the heat sealing line to lock the moving range of the layer group;

[0101] Step five: roll up the arm rod material along the long edge and fix it, and the arm rod is completed.

[0102] Figure 9 A more complete simulation vine inflatable arm structure is shown, 9-1 is the air pipe arranged on the inner wall material of the inflatable arm, and the air pipe port with appropriate size is opened on the surface of the arm rod material, and the air pipe is pasted at the air pipe port. 9-2 is a stop pin for fixing the rope 5-2, which can be pasted on the surface of the outer wall of the inflatable arm by double-sided adhesive tape and the like.

[0103] Reference Figures 10 to 12 The position control algorithm of the simulation vine inflatable arm is described.

[0104] The simulation vine inflatable arm in the state of few drivers and multiple degrees of freedom needs to specify joints when performing end trajectory tracking. The application first designs a joint controller as shown in Figure 10 , and then uses a sequential control algorithm to extend the joint controller to the whole arm.

[0105] The application introduces a method for establishing a joint controller. The controller generates a control input signal u based on the error e between the actual state and the desired state of the system, and the generalized coordinates, i.e. two quantities in the joint space (the turning angle ψ and the bending angle θ of the inflatable arm), can be obtained through forward dynamics. The generalized coordinates ξ are further transmitted back to the controller. To further improve the robustness and anti-interference ability of the system, a gravity compensation term G(ξ) is introduced in 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 formula (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 (ξ) is the Jacobian matrix of the end position with respect to the joint space variable; J q (ξ) is the Jacobian matrix of the generalized force mapping to the driving space.

[0108] The basis of the controller is a PD proportional-differential controller with a gravity compensation term, and the actual position x m of the end is obtained by an external sensing device The end velocity is obtained by differentiating the actual position and passing it through a low-pass filter to eliminate high-frequency noise. The two kinds of data are fed back to the host computer in real time. The filter can adopt the recursive form shown as follows:

[0109]

[0110] In the formula, k represents the current time step (the kth sampling); represents the original speed estimation at the current time k, which comes from the difference value; is the filtering result at the last time; is the filtering output at the current time, that is, the new speed value; and a is the filter coefficient, a ∈ (0, 1).

[0111] Before the control program shown in Figure 12 is performed, the introduction of offline trajectory optimization for preliminary trajectory tracking simulation experiments can improve the control accuracy and control efficiency. The present application 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 of each joint combination is analyzed, the minimum end error point is obtained by fmincon optimization, and the feasible trajectory is obtained by jtraj() interpolation, thereby providing a reference for the target position of each stage and reducing the overall search space. In the simulation environment, based on the characteristics of the generalized coordinates, each joint of the inflatable arm can be equivalent to a universal joint with two degrees of freedom, and the angle change is as shown in Figure 11 .

[0112] Figure 12The specific flow of the sequential control algorithm based on error threshold judgment is shown, the initial position of the end of the inflatable arm simulating rattan vine can be perceived by using external sensors such as a depth camera, and the error between the end of the inflatable arm simulating rattan vine and the target position can be obtained after position solving. In each stage, only the control sub-flow of the i th joint is activated, and the steering angle and bending angle of the joint are adjusted to the desired position. During the control process, the system will judge in real time whether the end position error meets the preset accuracy threshold, if it meets, it is determined that the current joint reaches the target state, and the control flow of the next joint i + 1 is entered, otherwise, it is further judged whether the convergence condition is met or whether the maximum control time is exceeded. If the error does not meet the accuracy 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 control times out and the target position is still not reached, the current stage control is terminated, and the next stage is entered according to the strategy.

[0113] Through the sequential control strategy, the stage driving control of the multi-section structure of the inflatable arm is realized, the coupling interference between the joints is effectively reduced, and the stability and trajectory tracking accuracy of the system are improved.

[0114] An electronic device includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0115] A computer readable storage medium for storing computer instructions, the computer instructions are executed by a processor to implement the steps of the above method.

[0116] The memory in the embodiments of the application can be a volatile memory or a nonvolatile memory, or can include both volatile and nonvolatile memory. Where the nonvolatile memory is a read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically EPROM (EEPROM), or flash memory. The volatile memory can be a random access memory (RAM), which is used as an external cache. By way of example, and not limitation, many forms of RAM are available, for example, 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). Note that the memory described herein is intended to include, among others, these and any other memory suitable for storing the data associated with the methods described herein.

[0117] In the above embodiments, all or part of the methods can be implemented by software, hardware, firmware, or any combination thereof. When implemented by software, all or part of the methods can be implemented 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, all or part of the processes or functions described in the embodiments of the present application are generated. 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 transferred from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center through a wired manner such as a coaxial cable, an optical fiber, a digital subscriber line (DSL), or a wireless manner such as infrared, wireless, microwave, etc. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server, data center, etc. that includes one or more available media sets. The available medium can be a magnetic medium such as a floppy disk, a hard disk, a magnetic tape, an optical medium such as a digital video disc (DVD), or a semiconductor medium such as a solid state disc (SSD), etc.

[0118] In the implementation process, each step of the above method can be completed by the integrated logic circuit of hardware in the processor or the instruction in the form of software. The steps of the method disclosed in the embodiments of the present application can be directly embodied as hardware processor execution or executed by a combination of hardware and software modules in the processor. The software module can be located in a random access memory, a flash memory, a read-only memory, a programmable read-only memory, an electrically erasable programmable memory, a register, or other mature storage media in the art. The storage medium is located in the memory, and the processor reads the information in the memory and combines the 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 the present application can be an integrated circuit chip with signal processing capability. In the implementation process, each step of the method embodiments can be completed by integrated logic circuits or instructions in the form of software of the hardware in the processor. The processor mentioned above can be a general processor, a digital signal processor DSP, an application specific integrated circuit ASIC, a field programmable gate array FPGA or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The disclosed methods, steps and logic block diagrams in the embodiments of the present application can be implemented or executed. The general processor can be a microprocessor or the processor can be any conventional processor. The steps of the method disclosed in combination with the embodiments of the present application can be directly embodied as hardware code processor execution completion, or executed by hardware and software module combination in the code processor. The software module can be located in the random access memory, the flash memory, the read only memory, the programmable read only memory or the electrically erasable programmable memory, the register and other mature storage media in the art. The storage medium is located in the memory, and the processor reads the information in the memory, and combines the hardware to complete the steps of the above method.

[0120] The above describes in detail the method for changing the rigidity of the rattan-like inflatable arm and the position control method thereof, and the principle and implementation mode of the present application are described. The above embodiment is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the above description should not be understood as the limitation of the present application.

Claims

1. A vine-like inflatable arm, characterized in that: the vine-like inflatable arm comprises a sealed base (1-1), an inflatable arm (1-2) and a recovery spool (1-3); the arm rod material of the inflatable arm (1-2) is wound on the recovery spool (1-3) in the initial stage, and when the air pressure in the sealed base (1-1) rises, the material of the inflatable arm (1-2) will evert, showing tip growth, and the inflatable arm elongates; the inflatable arm (1-2) is composed of a plurality of annular variable stiffness air bags (2-1) distributed along the axial direction, each annular variable stiffness air bag (2-1) comprises an inflatable arm inner wall material (8-1), an inflatable arm outer wall material (8-2) wrapped outside the inner wall material (8-1) and in contact with the outside world, and a sheet-shaped multi-layer structure layer group (2-2) between the inflatable arm outer wall material (8-2) and the inflatable arm inner wall material (8-1); the inflatable arm (1-2) is composed of the main cavity (2-3) region of the inflatable arm inner wall material (8-1); the multi-layer structure layer group (2-2) comprises a mixed material layer group (8-5) and a same material layer group (8-6), which are alternately arranged in the circumferential direction and have a gap (8-3) between adjacent layer groups; the annular variable stiffness air bag (2-1) changes the friction state between the layers by adjusting the internal pressure difference, realizing the local stiffness adjustable control of the vine-like inflatable arm.

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

3. The vine-like inflatable 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 inflatable arm inner wall material (8-1) and the inflatable arm outer wall material (8-2) by a heat sealing line (8-4), and the layers are overlapped together to form an air chamber to prevent the layer group from moving.

4. The vine-like inflatable arm according to claim 3, characterized in that: the vine-like inflatable arm further comprises three groups of motor-rope devices arranged uniformly at 120° in the circumferential direction, wherein 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 air bag (2-1) approaches zero, a steering joint is formed there, and by contracting the rope (5-2), a wrinkle is generated at the lowest stiffness, driving the inflatable arm to bend.

5. A variable stiffness method based on the vine-like inflatable arm according to any one of claims 1 to 4, characterized in that: the variable stiffness method comprises the following steps: step one: pressurize the main cavity (2-3) of the vine-like inflatable arm, drive the tip of the arm rod to evert, and characterize the elongation of the inflatable arm (1-2); stop pressurizing when the elongation reaches the desired length; step two: adjust the air pressure in a plurality of variable stiffness air bags (2-1); when the pressure difference approaches the air pressure in the main cavity (2-3), the layer group is subjected to the maximum degree of extrusion, and the stiffness of the inflatable arm at this variable stiffness air bag is improved. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ When the pressure difference approaches 0, the friction between layers is almost zero, the stiffness of the inflatable arm at the variable stiffness airbag is the lowest, and the variable stiffness airbag is converted into a steering joint; Step three, the rope (5-2) is retracted through the motor-rope device, a wrinkle is generated at the airbag (2-1) with the lowest stiffness, and steering control of the inflatable arm is realized.

6. The variable stiffness method according to claim 5, characterized in that: In step two, the air pressure of the airbag (2-1) is adjusted through a pneumatic circuit; The pneumatic circuit comprises 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, an air source (6-3) of the inflatable arm system, an electromagnetic proportional valve (6-4) for regulating the air pressure of the variable stiffness airbag, an electromagnetic reversing valve (6-5) for switching the direction of the air circuit, a pressure sensor (6-6) for detecting the air pressure in the variable stiffness airbag, and a vacuum generator (6-7) for vacuumizing the variable stiffness airbag to increase the pressure difference; When the stiffness of the arm needs to be increased, the electromagnetic reversing valve (6-5) is switched to the circuit where the vacuum generator (6-7) is located, the electromagnetic proportional valve (6-4) is regulated, the air pressure in the circuit is increased, and the gas flowing through the vacuum generator (6-7) will generate a corresponding vacuum degree in the variable stiffness airbag (2-1). At this time, the pressure difference in the airbag is the maximum, and the stiffness of the arm is the maximum; When the stiffness of the arm needs to be reduced, the electromagnetic reversing valve (6-5) is switched to the circuit where the pressure sensor (6-6) for detecting the air pressure in the variable stiffness airbag is located, the electromagnetic proportional valve (6-4) is regulated, and the air pressure in the circuit is close to the air pressure detected 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, and the stiffness of the arm is the minimum.

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 position control method specifically comprises the following steps: Step 1: Based on the end trajectory tracking task, sequentially activate the control of each joint by using a sequential control algorithm; Step 2: Perform closed-loop control on each activated joint; Real-time judge adaptive accuracy, error improvement and control time limit; Step 3: When any of the 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 of claim 7, wherein: In step 2, specifically, Adaptive accuracy judgment condition: Determine whether the current control has reached the accuracy threshold according to the end position error; Error improvement judgment condition: Use the reduction of error between consecutive samples to determine whether the end of the inflatable arm is approaching the target, i.e., whether it is converging; Control time limit condition: If the single-joint control time exceeds the specified time, forcibly terminate the current stage and enter the next stage to continue to complete the residual error compensation by the subsequent joint. 9.An electronic device comprising a memory and a processor, the memory storing a computer program, wherein, The processor executes the computer program to realize the steps of the position control method in claim 7 or 8.

10. A computer readable storage medium for storing computer instructions, characterized in that, The computer instructions are executed by the processor to realize the steps of the position control method in claim 7 or 8.

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