Soft crawling robot and preparation method thereof

Abstract

The invention provides a soft crawling robot and a preparation method thereof, and relates to the technical field of robots, the soft crawling robot comprises two spring drivers and two foot structures; each spring driver comprises a rear end cover and a front end cover, a rear end ventilation sleeve is arranged in the rear end cover, a front end ventilation sleeve is arranged in the front end cover, a spring is arranged between the rear end ventilation sleeve and the front end ventilation sleeve, and the rear end ventilation sleeve and the front end ventilation sleeve are arranged outside the spring in a sleeving mode. The rear end ventilation sleeve, the front end ventilation sleeve, the rear end cover and the front end cover are jointly closed to form a vacuum air bag with a sealed cavity. The vacuum air bag is connected with an air pipe and is connected with an external vacuum pump through the air pipe to provide negative pressure; and foot structures are respectively arranged at the bottom of the front end cover and the bottom of the rear end cover of the spring driver. By adopting a double-driver structure and a driving mode that the vacuum air bag is matched with the spring, linear motion and steering motion can be achieved, and motion flexibility and terrain adaptability are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of robotics, and in particular to a soft crawling robot and its manufacturing method. Background Technology

[0002] Soft robots, due to their soft materials, strong structural adaptability, and high compatibility with complex environments, have become an important research direction in the field of intelligent robotics in recent years. Compared with traditional rigid robots, soft robots can move flexibly in irregular and unstructured environments, making them suitable for many scenarios such as medical intervention, disaster search and rescue, industrial inspection, and biomimetic research.

[0003] Soft crawling robots, as a representative type of structure mimicking slow-moving terrestrial organisms such as worms and caterpillars, have seen some progress in research. In existing technologies, soft crawling robots often employ pneumatic, hydraulic, dielectric elastomer, and shape memory alloy actuation methods, combined with certain friction control mechanisms, to achieve forward or turning motion. However, in practical research, we have found that these robots typically also face some technical challenges: (1) Weak turning ability: Most soft robots can only achieve unidirectional crawling movement, lack flexible directional control ability, and are difficult to adapt to complex routes or environments.

[0004] (2) Poor motion stability: The friction mechanism or suction cup structure of traditional robot feet is difficult to maintain attachment on vertical or smooth surfaces, affecting the stability of motion and effective load capacity.

[0005] (3) Short lifespan: Traditional robots may experience material fatigue during repeated deformation. Some dielectric or hydraulic systems have slow response speeds and are not easy to precisely control the deformation amplitude and direction. Summary of the Invention

[0006] To address the technical problems of weak steering ability, poor motion stability, and short lifespan in existing metamaterial structures, this invention provides a soft crawling robot and its fabrication method.

[0007] The technical solutions provided by the embodiments of the present invention are as follows: A first aspect of the present invention provides a soft crawling robot, comprising: two spring actuators and two foot structures; each spring actuator includes a rear end cover and a front end cover, a rear end ventilation sleeve is disposed inside the rear end cover, a front end ventilation sleeve is disposed inside the front end cover, a spring is disposed between the rear end ventilation sleeve and the front end ventilation sleeve, the rear end ventilation sleeve and the front end ventilation sleeve are sleeved outside the spring, the rear end ventilation sleeve, the front end ventilation sleeve, the rear end cover and the front end cover together seal to form a vacuum bladder with a sealed chamber; an air tube is connected to the vacuum bladder, and an external vacuum pump is connected through the air tube to provide negative pressure; the foot structures are respectively disposed at the bottom of the front end cover and the bottom of the rear end cover of the spring actuator.

[0008] Optionally, the axial contraction of the spring is controlled by the negative pressure of the vacuum chamber, and the spring returns to its length under the action of elastic force after the negative pressure is released.

[0009] Optionally, the foot structure includes: a dielectric layer, interdigitated electrodes, and an electrode encapsulation layer arranged sequentially from bottom to top; the dielectric layer and the interdigitated electrodes are stacked to form an electroadhesion structure, and a high-voltage electric field is generated by the interdigitated electrodes, so that the electroadhesion structure generates an adhesive force with the ground, thereby achieving adhesion or detachment control.

[0010] Optionally, the soft crawling robot can achieve two movement modes—forward and turning—by switching between the adhesion state of its foot structure and the extension / retraction state of its body structure.

[0011] Optionally, a rotating connector and a bearing are provided between the spring actuator and the foot structure to alleviate foot deflection caused by spring torsion and improve adhesion stability.

[0012] Optionally, an antenna is provided at the front end of the front end cover, each antenna including a PET skeleton and a resistive contact sensor.

[0013] Optionally, the resistive contact sensor includes: a conductive polyurethane foam core coated with conductive silver paste; when the conductive polyurethane foam core is subjected to external force and comes into contact with an obstacle, the resistance of the conductive polyurethane foam core increases, thereby realizing contact sensing.

[0014] A second aspect of this invention provides a method for manufacturing a soft crawling robot, comprising: S1. Preparation of spring actuator: The spring is placed between the rear vent sleeve and the front vent sleeve, and the front cover and rear cover vacuum bag are sealed at both ends to form a vacuum bag with a sealed chamber. A vacuum tube is connected to the vacuum bag to form a vacuum drive structure. S2. Preparation of foot structure: Interdigital electrodes are prepared by laser cutting copper foil. The interdigital electrodes are then attached to a PI film. Liquid Ecoflex-0050 silicone rubber mixture is poured onto the surface of the interdigital electrodes. After standing at 50°C for 30 minutes, an electrode encapsulation layer is directly obtained on the surface of the interdigital electrodes. This layer can isolate air and prevent repeated electrode breakdown, which would cause the foot to lose its adhesion. S3. Fabrication of resistive contact sensor: Polyurethane foam is foamed and molded, and CB / PDMS conductive composite material is impregnated to form a conductive polyurethane foam core. Then, conductive silver paste is used to fix the electrode leads, and the resistive contact sensor is installed on the antenna. S4. Assembly: First, set the two spring actuators side by side, then connect the foot structure to the end cap of the spring actuator; finally, connect the contact angle at the front end of the spring actuator.

[0015] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: (1) In the embodiments of the present invention, by adopting a dual-drive structure and a vacuum airbag combined with a spring drive method, controllable axial contraction and recovery are achieved, which has good motion response speed and drive efficiency, and can realize linear motion and steering motion, significantly improving motion flexibility and terrain adaptability.

[0016] (2) In this embodiment of the invention, by setting foot electroadhesion structures at the front and rear ends of the spring actuator, it can adhere to and walk on various surfaces such as glass, metal, and wood, thereby enhancing the adhesion stability and obstacle crossing ability. At the same time, it is also convenient to turn when working with the spring actuator.

[0017] (3) In this embodiment of the invention, by setting a resistive contact sensor at the front end of the spring driver, it is made to have the ability to perceive contact with external obstacles in real time, and the contact signal can be fed back to the control system to realize environmental interactive perception and active obstacle avoidance, thereby improving the intelligence level of the robot. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a structural schematic diagram of a soft crawling robot provided in an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of a single spring actuator structure provided in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of an antenna structure provided in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of an electroadhesive foot structure provided in an embodiment of the present invention.

[0023] Reference numerals: 1. Spring actuator; 2. Foot structure; 3. Antennae; 4. Rear end cap; 5. Rear end vent sleeve cap; 6. Vacuum bladder; 7. Spring; 8. Front end vent sleeve; 9. Front end cap; 10. PET skeleton; 11. Resistive contact sensor; 12. Dielectric layer; 13. Interdigital electrode; 14. Electrode encapsulation layer.

[0024] As shown in the figure, specific structures and devices are marked in the figure to clearly illustrate the structure of the embodiments of the present invention. However, this is only for illustrative purposes and is not intended to limit the present invention to this specific structure, device and environment. Those skilled in the art can adjust or modify these devices and environments according to specific needs. Detailed Implementation

[0025] The technical solutions of the present invention will now be described with reference to the accompanying drawings. It should also be noted that, to make the embodiments more detailed, the following embodiments are the best and preferred embodiments. For some well-known technologies, those skilled in the art can also use other alternative methods to implement the invention; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0026] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0027] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.

[0028] It is understood that the meanings of “on”, “above”, and “above” in this invention should be interpreted in the broadest manner, such that “on” not only means “directly on” something, but also includes the meaning of being “on” something with an intervening feature or layer, and that “above” or “above” not only means “on” something, but also includes the meaning of being “on” something without an intervening feature or layer.

[0029] Furthermore, spatially related terms such as “below,” “under,” “lower,” “above,” and “upper” are used herein for convenience to describe the relationship of one element or feature to one or more other elements or features, as illustrated in the accompanying drawings. Spatially related terms are intended to cover different orientations in the use or operation of the device other than those depicted in the accompanying drawings. The device may be oriented in other ways, and the spatially related descriptive terms used herein can be interpreted similarly.

[0030] like Figures 1 to 4 As shown, an embodiment of the present invention provides a soft crawling robot, comprising: two spring actuators 1 and two foot structures 2; each spring actuator 1 includes a rear end cover 4 and a front end cover 9, a rear end ventilation sleeve 5 is disposed inside the rear end cover 4, a front end ventilation sleeve 8 is disposed inside the front end cover 9, a spring 7 is disposed between the rear end ventilation sleeve 5 and the front end ventilation sleeve 8, the rear end ventilation sleeve 5 and the front end ventilation sleeve 8 are sleeved on the outside of the spring 7, and the rear end ventilation sleeve 5, the front end ventilation sleeve 8, the rear end cover 4 and the front end cover 9 together seal to form a vacuum bladder 6 with a sealed chamber; optionally, the vacuum bladder 6 is heat-sealed using a low-density polyethylene film, which has good flexibility, airtightness and pressure resistance.

[0031] The vacuum bladder 6 is connected to an air tube, which connects to an external vacuum pump to provide negative pressure. Optionally, the axial contraction of the spring 7 is controlled by the negative pressure of the vacuum chamber. When the negative pressure is released, the spring 7 returns to its original length under the action of elastic force. During vacuum suction, the air pressure inside the chamber drops rapidly, and the spring 7 contracts axially, causing the entire spring actuator 1 to undergo axial shortening motion. When the negative pressure is released, the spring 7 returns to its original length due to its own elasticity. The spring 7 mainly acts as a skeleton, not only constraining the radial expansion of the air bladder but also allowing it to quickly return to its original state after the vacuum is released, thereby achieving high-frequency motion cycles.

[0032] Furthermore, by adjusting the negative pressure supply of the two spring actuators 1, multiple modes such as single-sided drive and alternating double-sided drive can be achieved. In particular, by combining single-sided drive with friction difference, clockwise or counterclockwise steering can be formed, enabling flexible obstacle avoidance. The two spring actuators 1 are structurally symmetrical and independent, and can be connected to independent vacuum control channels respectively. Combined with the independent adhesion states of the left and right foot structures, a multi-degree-of-freedom, highly controllable differential motion mode can be achieved.

[0033] Furthermore, to improve structural compliance and accommodate body torsion, the two spring actuators are connected by a flexible connector, allowing the robot body to bend locally, providing a basis for complex movements.

[0034] The foot structure 2 is provided at the bottom of the front end cover 9 and the bottom of the rear end cover 4 of the spring actuator 1, respectively.

[0035] The robot adopts a modular design, with each component assembled through flexible connectors. It has good structural adaptability and motion coordination, and is suitable for autonomous movement and environmental perception tasks in scenarios such as confined spaces and complex terrains.

[0036] Optionally, the foot structure 2 includes: a dielectric layer 12, interdigitated electrodes 13, and an electrode encapsulation layer 14 arranged sequentially from bottom to top; the dielectric layer 12 and the interdigitated electrodes 13 are stacked to form an electroadhesion structure, and a high-voltage electric field is generated by the interdigitated electrodes 13, so that the electroadhesion structure generates an adhesive force with the ground, thereby achieving adhesion or detachment control.

[0037] The dielectric layer 12 can be made of polyimide (PI) film, the interdigitated electrode layer 13 can be made of copper foil or other highly conductive flexible materials, the electrode encapsulation layer 14 can be made of Ecoflex flexible silicone rubber, the electrode layer is connected to the control system, and an electric field is applied through a high voltage amplifier to form a controllable electroadhesion force between the foot and the ground, thereby achieving stable adhesion of the robot to various surfaces such as glass, metal, paper, and wood.

[0038] By setting foot electroadhesion structures at the front and rear ends of the spring actuator, it can adhere to and walk on various surfaces such as glass, metal, and wood, enhancing adhesion stability and obstacle-crossing ability. At the same time, it also facilitates steering when used in conjunction with the spring actuator.

[0039] Optionally, the soft crawling robot can achieve two movement modes, forward movement and turning, by switching between the adhesion state of the foot structure 2 before and after and the extension and contraction state of the body structure.

[0040] When the on / off state of the foot structure 2 is coordinated with the vacuum actuation state of the spring actuator 1, effective forward and turning movements can be achieved. The robot's forelegs and hind legs can be controlled independently, and the movements of each part are driven by a precise timing logic control system, thereby completing continuous peristaltic forward movement or turning operations.

[0041] Furthermore, the robot's forelegs and hindlegs can be independently controlled for adhesion and coordinated with the vacuum drive cycle. By setting a specific start-stop sequence through the control program, stable straight-line forward movement, turning in place, and rapid stopping can be achieved.

[0042] In this invention, by adopting a dual-drive structure and a vacuum airbag combined with a spring drive method, controllable axial contraction and recovery are achieved, which has good motion response speed and drive efficiency, and can realize linear motion and steering motion, significantly improving motion flexibility and terrain adaptability.

[0043] Optionally, to prevent the torsion generated by the spring actuator during contraction from affecting the foot attachment accuracy, a rotating connector and bearing are provided between the spring actuator 1 and the foot structure 2. This can alleviate foot deflection caused by the torsion of the spring 6, improve attachment stability, and ensure that the foot always maintains a good fit on the adsorption surface.

[0044] Optionally, an antenna 3 is provided at the front end of the front end cover 9, and each antenna 3 includes a PET skeleton 10 and a resistive contact sensor 11.

[0045] By setting a resistive contact sensor at the front end of the spring actuator, it can have the ability to perceive contact with external obstacles in real time and can feed the contact signal back to the control system, realizing environmental interactive perception and active obstacle avoidance, thus improving the robot's intelligence level.

[0046] Optionally, the resistive contact sensor 11 includes: a conductive polyurethane foam core coated with conductive silver paste; when the conductive polyurethane foam core is subjected to external force and comes into contact with an obstacle, the resistance of the conductive polyurethane foam core increases, thereby realizing contact sensing.

[0047] The resistive contact sensor 11 integrates sensing function, structural support, and controllable deformation capability. Its internal core is a porous honeycomb conductive polyurethane foam core. After the foam is produced by the foaming process, it is further impregnated with CB / PDMS conductive composite suspension to obtain resistive strain characteristics. Two electrode wires are respectively bonded to the upper and lower surfaces of the foam core to form a complete sensing path. The wires are coated with silver paste for high adhesion to ensure stable contact.

[0048] Furthermore, a silicone tube is inserted into the center of the foam core to regulate internal air pressure, thereby achieving internal contraction and recovery. The foam is encapsulated with a rubber film, forming a flexible and airtight structure with good recoverability and environmental adaptability. As a biomimetic antenna, the SSTA deforms under pressure when its tip contacts an obstacle, altering the conductive network inside the foam and changing its resistance. This resistance change can be transmitted to a control unit such as a microcontroller via a voltage acquisition circuit, triggering actions such as stopping or turning, thus forming a closed-loop control process.

[0049] In addition, since different contact materials (such as rigid metals, flexible foams, etc.) have different piezoresistive feedback to conductive foam, SSTA also has a certain material discrimination capability and can be used as a robot "tactile perception" module. This structure does not require external power supply and outputs signals by relying on self-sensing mechanism, and has the characteristics of low energy consumption, compact structure and sensitive response.

[0050] The soft crawling robot of this invention adopts a modular structure, making it lightweight, flexible, and highly compliant. The spring actuator, constructed through an encapsulated pneumatic cavity and an elastic return spring 7, exhibits high responsiveness, high repeatability, and good controllability. The electroadhesive structure of the feet can adapt to various surfaces, ensuring stable adhesion. The integrated resistive contact sensor at the front end not only possesses motion capabilities but also dual functions of body perception and external perception, effectively improving the robot's ability to cope with unknown environments.

[0051] Specifically, when working, if linear forward movement is required, the control process is as follows: front feet adhere → body retracts → hind feet adhere → front feet release → spring rebounds → propels the robot to move. If a turn is required, the control process is as follows: control only one side of the spring actuator to work while the other side remains stationary, and achieve the rotation of the robot body through asymmetrical deformation; in conjunction with the foot movement switching, it can achieve rotation in place or arc turning.

[0052] Experiments have verified that this soft crawling robot performs excellently in terms of compliance, adhesion, load capacity, and dynamic response speed. It can achieve a maximum turning speed of 15.09 rad / s, carry a load of 69 times its own weight, and climb vertical walls at a speed of 6.67 mm / s, possessing a variety of complex motion capabilities.

[0053] This invention provides a method for manufacturing a soft crawling robot, comprising: S1. Preparation of spring actuator 1: Place spring 7 between rear vent sleeve 5 and front vent sleeve 8, and seal front cover 9 and rear cover 4 at both ends to form vacuum bag 6 with sealed chamber. Connect vacuum tube to vacuum bag 6 to form vacuum drive structure. S2. Preparation of foot structure: Interdigital electrodes 13 are prepared by laser cutting copper foil. The interdigital electrodes 13 are then attached to a PI film. Liquid Ecoflex-0050 silicone rubber mixture is poured onto the surface of the interdigital electrodes 13. After standing at 50°C for 30 minutes, an electrode encapsulation layer 14 is directly obtained on the surface of the interdigital electrodes 13. This layer can isolate air and prevent repeated electrode breakdown, which would cause the foot to lose its adhesion. S3. Fabrication of resistive contact sensor: Polyurethane foam is foamed and molded, and CB / PDMS conductive composite material is impregnated to form a conductive polyurethane foam core. Then, conductive silver paste is used to fix the electrode leads, and the resistive contact sensor is installed on the antenna 3. Specifically, polyurethane foam can be foamed and molded, then impregnated with CB / PDMS conductive suspension, and then the foam is placed on a 90°C heating platform for drying. It is then repeatedly washed with hexane solution to remove excess conductive particles and solvent residue, thereby improving the signal stability and repeatability of the conductive foam. Subsequently, silver paste is sprayed to form a conductive network, and wires, rubber membranes and silicone tubes are assembled to form a closed structure.

[0054] S4. Assembly: First, set the two spring actuators 1 side by side, then connect the foot structure 2 to the end cap of the spring actuator 1; finally, connect the contact angle 3 to the front end of the spring actuator 1.

[0055] With the above structure, this soft crawling robot can achieve effective linear propulsion and directional control, and has good motion stability and adaptability in unstructured environments. It is particularly suitable for high-requirement tasks such as monitoring, inspection, and detection, and has broad application prospects.

[0056] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the preferred embodiments, while those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A soft crawling robot, characterized in that, include: Two spring actuators (1) and two foot structures (2); each spring actuator (1) includes a rear end cover (4) and a front end cover (9), a rear end ventilation sleeve (5) is provided inside the rear end cover (4), a front end ventilation sleeve (8) is provided inside the front end cover (9), a spring (7) is provided between the rear end ventilation sleeve (5) and the front end ventilation sleeve (8), the rear end ventilation sleeve (5) and the front end ventilation sleeve (8) are sleeved on the outside of the spring (7), the rear end ventilation sleeve (5), the front end ventilation sleeve (8), the rear end cover (4) and the front end cover (9) together seal to form a vacuum bag (6) with a sealed chamber; an air tube is connected to the vacuum bag (6), and an external vacuum pump is connected through the air tube to provide negative pressure; the foot structures (2) are respectively provided at the bottom of the front end cover (9) and the bottom of the rear end cover (4) of the spring actuator (1).

2. The soft crawling robot according to claim 1, characterized in that, The axial contraction of the spring (7) is controlled by the negative pressure of the vacuum chamber. When the negative pressure is released, the spring (7) recovers its length under the action of elastic force.

3. The soft crawling robot according to claim 1, characterized in that, The foot structure (2) includes a dielectric layer (12), interdigitated electrodes (13) and an electrode encapsulation layer (14) arranged sequentially from bottom to top. The dielectric layer (12) and the interdigitated electrodes (13) are stacked to form an electroadhesion structure. A high voltage electric field is generated through the interdigitated electrodes (13), so that the electroadhesion structure generates an adhesive force with the ground, thereby achieving adhesion or detachment control.

4. The soft crawling robot according to claim 1, characterized in that, The soft crawling robot achieves two movement modes: forward movement and turning movement by switching the adhesion state of the foot structure (2) before and after and the extension and contraction state of the body structure.

5. The soft crawling robot according to claim 1, characterized in that, A rotating connector and bearing are provided between the spring actuator (1) and the foot structure (2) to alleviate foot deflection caused by the torsion of the spring (6) and improve adhesion stability.

6. The soft crawling robot according to claim 1, characterized in that, The front end of the front end cover (9) is provided with an antenna (3), each of the antennas (3) including: a PET skeleton (10) and a resistive contact sensor (11).

7. The soft crawling robot according to claim 6, characterized in that, The resistive contact sensor (11) includes: a conductive polyurethane foam core coated with conductive silver paste; when the conductive polyurethane foam core is subjected to external force and comes into contact with an obstacle, the resistance of the conductive polyurethane foam core increases, thereby realizing contact sensing.

8. A method for manufacturing a soft crawling robot, characterized in that, include: S1. Preparation of spring actuator (1): Place the spring (7) between the rear ventilation sleeve (5) and the front ventilation sleeve (8), and seal the front cover (9) and the rear cover (4) at both ends to form a vacuum bag (6) with a sealed chamber. Connect the vacuum tube to the vacuum bag (6) to form a vacuum drive structure. S2. Preparation of foot structure: The interdigital electrode (13) is prepared by laser cutting copper foil. The interdigital electrode (13) is attached to the PI film. Liquid Ecoflex-0050 silicone rubber mixture is poured on the surface of the interdigital electrode (13). After standing at 50°C for 30 minutes, an electrode encapsulation layer (14) is directly obtained on the surface of the interdigital electrode (13). This can isolate the air and prevent the electrode from being repeatedly broken down, which would cause the foot to lose its adhesion. S3. Preparation of resistive contact sensor: Polyurethane foam is foamed and molded, CB / PDMS conductive composite material is impregnated to form a conductive polyurethane foam core, and then the electrode leads are fixed with conductive silver paste. The resistive contact sensor is installed on the antenna (3). S4. Assembly: First, set the two spring actuators (1) side by side, then connect the foot structure (2) to the end cap of the spring actuator (1); finally, connect the contact angle (3) to the front end of the spring actuator (1).

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