Multi-motion-mode miniature soft robot driven by shape memory alloy

Abstract

The invention provides a multi-motion-mode miniature soft robot driven by shape memory alloy. The multi-motion-mode miniature soft robot comprises an elastic framework, an SMA driver and a mechanism bottom passive friction device. The SMA drivers are fixed to the front face and the back face of the elastic framework. The mechanism bottom passive friction device is fixed at the tail end of the elastic framework; the elastic framework is used for providing pre-deformation of the SMA driver at room temperature and enabling the SMA driver to recover to an initial pre-deformation form by utilizing elastic potential energy; the SMA driver is used for axial compression under heating of an external electric field, the elastic framework fixedly connected with the SMA driver is bent and deformed unidirectionally due to generated pulling force, and therefore propulsive force is generated to drive the robot to achieve a preset motion mode. The mechanism bottom passive friction device is used for achieving a one-way friction force structure, and directional crawling of the robot is achieved. The soft robot system has high motion flexibility and adaptability, and can perform diversified motion and exploration in a complex environment.

Description

Technical Field

[0001] The present invention relates to the technical field of soft robots, and in particular to a multi-motion mode micro soft robot driven by a shape memory alloy. Background Art

[0002] Robots made of rigid materials have achieved remarkable development in the past few decades. These robots are designed for specific tasks or groups of tasks, with efficient task specificity and excellent precision. Rigid materials endow robots with remarkable high precision, enabling them to achieve accurate movement and control during operation. However, the inflexibility of rigid robots limits their adaptability in different tasks and environments, especially the lack of safety and flexibility in dynamic environments.

[0003] In order to meet diverse needs, scientists have begun to draw inspiration from invertebrates and plants to study continuum robots and soft robots. Soft robots are made of flexible materials similar to biological tissues. Their design and manufacturing process inherently give them softness and compliance, enabling them to perform a variety of tasks that rigid robots cannot, such as deep-sea exploration, diving operations, and complex surface movements.

[0004] The deformability of soft robots makes them very suitable for coping with movements in complex unstructured environments. Researchers have developed a variety of efficient and reliable soft robot configurations and designs for tasks in different environments, including oceans, pipelines, vertical planes, etc. These soft robots show specific high efficiency, but most of them are only applicable to specific environments, which severely limits their capabilities and range in different movement environments.

[0005] In the real world, amphibian animals usually have multiple motion modes to adapt to the movement needs in different environments. Based on the idea of ​​bionics, soft robots achieve multimodal motion through the design of clever mechanical structure and drive mode, imitating the movement mode of amphibian animals to adapt to different environments. At present, there are some representative works at home and abroad, such as:

[0006] Salamander-like amphibious soft robot: This soft robot can swim like an eel in water and crawl on land. The robot generates wave-like motion by swinging its body, and propels itself through interaction with the environment. The robot's movement speed is positively correlated with the frequency of the wave, and the robot can adjust its direction and posture by changing the curvature.

[0007] Jumping origami soft robot: This soft robot uses shape memory alloys as muscles, and can jump by adjusting its shape and exerting force, adapting to narrow and complex spaces.

[0008] Small Insect-like Amphibious Robot: This miniature insect-like robot can fly, walk, and adapt to land, air and water environments.

[0009] Patent document CN110076749A (application number: CN201910503103.2) discloses a jellyfish-like magnetically controlled micro soft robot, comprising a head located on the same plane and five movable arms evenly distributed in the circumferential direction of the head and arranged radially; wherein the movable arms include an upper arm, a forearm and a hand; the head, the upper arm, the forearm and the hand are connected in sequence by elastic tendons; the head, the upper arm, the forearm and the hand are all rigid parts with different magnetic field directions, so that the five movable arms can move in multiple degrees of freedom under the action of an external magnetic field and can bend and embrace into a dodecahedron-like body under the action of an external magnetic field.

[0010] Although the above research has partially solved the problem of applying soft robots in complex environments, there are still many challenges, such as dealing with uneven roads and low obstacles. Studies have shown that the rolling ability of soft robots may have potential in this regard, but current research is relatively limited. Summary of the invention

[0011] In view of the defects in the prior art, the purpose of the present invention is to provide a multi-motion mode micro soft robot driven by a shape memory alloy.

[0012] The shape memory alloy driven multi-motion mode micro soft robot provided by the present invention comprises: an elastic skeleton, an SMA driver and a passive friction device at the bottom of the mechanism;

[0013] The SMA driver is fixed on the front and back sides of the elastic frame;

[0014] The passive friction device at the bottom of the mechanism is fixed to the end of the elastic frame;

[0015] The elastic skeleton is the main body of the robot mechanism, and is used to provide pre-deformation of the SMA actuator at room temperature, and utilize elastic potential energy to restore the SMA actuator in a relaxed state to the initial pre-deformed state;

[0016] The SMA actuator is used to axially compress under external electric field heating, and the generated tension causes the elastic skeleton connected thereto to be unidirectionally bent and deformed, thereby generating a propulsion force to drive the robot to achieve a preset motion mode;

[0017] The passive friction device at the bottom of the mechanism is used to realize a unidirectional friction structure, realize the directional crawling of the robot, and enable the basic movement ability of the robot.

[0018] Preferably, the SMA actuator is an orthodontic tension spring.

[0019] Preferably, it also includes auxiliary materials: power cord and heat-insulating tape;

[0020] The power line is connected to an external power source and the SMA driver to provide a working current for the SMA driver;

[0021] The heat-insulating adhesive tape is adhered to the front and back surfaces of the elastic frame.

[0022] Preferably, the elastic skeleton selection requirements include two factors: one is to provide sufficient support force to achieve the desired pre-deformation degree of the SMA actuator, and the other is to provide sufficiently large elastic potential energy as a restoring force to ensure that the SMA actuator switches between the extension and contraction states.

[0023] Preferably, the SMA actuator selection requirements include: considering the responsiveness to temperature, deformation rate and maximum load; considering that when the robot performs crawling and jumping movements, the SMA actuator needs to generate a sufficiently large pulling force so that the bending degree of the elastic skeleton can meet the task requirements.

[0024] Preferably, the selection of the power cord includes two factors: one is to ensure that the SMA driver can stably provide a sufficiently large working current; the other is to use a lightweight wire material so as not to affect the movement of the robot.

[0025] Preferably, the thermal insulation tape uses a double layer of thermal insulation tape as the thermal insulation layer, with the glue surfaces adhered to each other and the non-glue surfaces facing outwards.

[0026] Preferably, the assembly process is:

[0027] Step S1: integrating the selected materials;

[0028] Step S2: Based on energy conservation, the robot motion modeling and analysis are performed;

[0029] Step S3: designing a bistable structure to expand the jumping function of the mechanism;

[0030] Step S4: According to the driving mechanism of the SMA actuator, a control method of connecting a switch circuit in series with the SMA actuator is adopted to achieve effective control of the temperature of the SMA actuator.

[0031] Preferably, step S2 comprises:

[0032] Assuming the initial bending angle of the elastic skeleton is 0, the strain energy stored in the plate due to bending relative to θ is:

[0033]

[0034] The tensile strain energy in the SMA actuator is:

[0035]

[0036] Where, under different conditions of the corresponding bending angle θ, when θ<0, it means that the elastic skeleton is bent downward; when θ>0, it means that the elastic skeleton is bent upward; in each, the first term corresponds to the strain energy of the SMA actuator placed on the lower side of the elastic skeleton; the second term corresponds to the strain energy of the SMA actuator on the upper side of the elastic skeleton; assuming that the deformation of the SMA actuator is linearly related to the temperature, L max , L0 represent the stretched length and initial length of the SMA actuator, respectively; k1 and k2 represent the SMA spring stiffness;

[0037] The total potential energy of the system during bending is: U t =U SMA +U bend .

[0038] Preferably, step S3 includes: designing the initial state of the mechanism to be a straight line, combining energy distribution and stretching potential energy to make the total energy in the mechanism symmetrically distributed, heating the SMA actuators on both sides, and increasing the stiffness k of the SMA actuators, so that the total energy of the system has two symmetrical local minimum points on the left and right sides, that is, two stable states. In this way, the SMA actuator stores / releases energy during the bending process, generates instantaneous dynamics after the energy peak, and drives the robot to jump and climb over as a whole.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention provides a shape memory alloy driven multi-motion mode micro soft robot. In addition to traditional crawling motion, the bistable structure adopted by the robot additionally gives it jumping ability, which can climb over obstacles and improve the applicability of exploration tasks in rugged obstacle environments. The soft robot system of the present invention has a high degree of motion flexibility and adaptability, and can perform diversified motion and exploration in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0042] Figure 1 Schematic diagram of the soft robot system;

[0043] Figure 2 This is a schematic diagram of the crawling motion of the soft robot;

[0044] Figure 3 It is a schematic diagram of the bending state;

[0045] Figure 4 This is the system energy distribution diagram. DETAILED DESCRIPTION

[0046] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0047] Example

[0048] The present invention provides a shape memory alloy driven multi-motion mode micro soft robot, comprising an elastic skeleton, an SMA driver and a passive friction device at the bottom of the mechanism;

[0049] The SMA actuator is used for axial compression under external electric field heating, and the tension generated causes the elastic skeleton connected to it to bend unidirectionally, thereby generating sufficient propulsion force to drive the robot to achieve a specific motion mode. Based on the results of domestic market research, an economical orthodontic tension spring is selected as the actuator;

[0050] The elastic skeleton is used as the main body of the robot mechanism to provide pre-deformation of the SMA spring at room temperature, and use the elastic potential energy to restore the SMA spring in the relaxed state (non-working state) to the initial pre-deformed state. Combined with the SMA spring selection results and the tension generated when it is at its maximum deformation (assuming the bending angle at this time is), the elastic skeleton selection and geometric parameters are determined by analyzing and testing the support force and elastic potential energy that can be provided by raw materials of different models and different geometric sizes;

[0051] The passive friction device at the bottom of the mechanism is used to realize a unidirectional friction structure, realize the directional crawling of the robot, and enable the basic movement ability of the robot;

[0052] The shape memory alloy driven multi-motion mode micro soft robot provided by the present invention also includes auxiliary materials power cord and heat insulation tape;

[0053] The power cord is connected to an external power source to provide working current for the SMA spring, and the current and diameter of the power cord are determined based on the selected SMA driver parameters and the principle of not affecting the movement of the robot;

[0054] The thermal insulation tape is placed between the power cord and the elastic skeleton as an insulation layer, which can protect the elastic skeleton to a certain extent and prevent the internal elastic skeleton material from melting when the temperature is too high when the power is turned on or the heating time is too long, thereby damaging the mechanism and causing movement failure. In order to prevent the adhesion of the thermal insulation tape from generating damping during the bending process of the elastic skeleton, ensure the SMA driving effect, and at the same time avoid direct contact between the power cord and the elastic skeleton to cause damage to the mechanism, a double-layer thermal insulation tape (the glue surfaces are adhered to each other and the non-glue surfaces face outwards) is used as the insulation layer.

[0055] Integration of the above selected materials:

[0056] The elastic skeleton raw materials are laser cut to obtain the elastic skeletons of each leg mechanism of the bipedal robot. Double layers of thermal insulation tape are adhered to the front and back sides as thermal insulation layers, and SMA springs are fixed on the front and back sides respectively. The specific value of the distance between the two fixed end points of the spring is adjusted according to the design requirements to achieve the required performance.

[0057] The constructed mechanism is modeled and analyzed based on the energy conservation method. The total energy of the system is mainly composed of two main parts: the deformation potential energy of the elastic skeleton (bending potential energy) and the potential energy of the stretching spring (stretching potential energy). These two parts are related to the initial shape of the elastic skeleton and the initial length and stiffness of the spring, respectively. Both bending and stretching energy can be approximated using a function of the bending angle θ, such as Figure 3 shown.

[0058] Assuming the initial shape of the elastic skeleton is a bending angle of 0, the strain energy stored in the plate due to bending about θ is:

[0059]

[0060] The tensile strain energy in an SMA spring is:

[0061]

[0062] In the above formula, under different conditions of θ, when θ<0, it means that the elastic skeleton is bent downward; correspondingly, when θ>0, it means that the elastic skeleton is bent upward. In each formula, the first term corresponds to the strain energy of the SMA spring placed on the lower side of the elastic skeleton; the second term corresponds to the strain energy of the SMA spring on the upper side of the elastic skeleton. It should be pointed out that in order to simplify the calculation process, it is assumed here that the SMA deformation is linearly related to temperature. L max , L0 represent the stretched length and initial length of the SMA spring respectively; k1 and k2 represent the stiffness of the SMA spring. Therefore, the total potential energy of the system during bending can be calculated as:

[0063] U t =U SMA +U bend

[0064] Based on the overall energy analysis of the system, a bistable structure is designed for the prototype, and the jumping function of the prototype system is expanded: the initial state of the design mechanism is a straight line (the bending angles of each foot are 0 in the initial state). In this case, the bending potential energy is a parabola with a minimum value at a bending angle of 0. Combining energy distribution and stretching potential energy, the total energy in the mechanism can be distributed symmetrically. See the energy distribution diagram of the system for details. Figure 4 .

[0065] The total energy distribution in the structure has a minimum when the bending angle is 0, that is, a stable state. If the SMA springs on both sides are heated, the spring stiffness k increases, so that the total energy of the system has two symmetrical local minimum points on the left and right sides, that is, two stable states. In this way, the drive module can store / release energy during the bending process, generate instantaneous dynamics after the energy peak, and drive the robot to jump and climb over as a whole.

[0066] According to the driving mechanism of the SMA spring, a control scheme in which a switch circuit is connected in series with the SMA spring is adopted to achieve effective control of the temperature of the SMA spring: when the resistance of the SMA spring is fixed, the heating power of the spring is proportional to the square of the current passing through the spring. Therefore, the control circuit needs to be able to independently control the power on and off of each SMA spring, and when powered on, it can control the current passing through the spring to control the heating speed. Through the query of relevant information, this study decided to adopt a control scheme in which a general current controller is connected in series with the SMA spring. When the load end voltage is large enough and does not exceed the maximum allowable voltage of the current controller, the current controller operates in the constant current region, and the current passing through the SMA spring is directly determined by the current controller, thereby achieving control of the temperature of the SMA spring.

[0067] This project finally decided to use a multi-channel current control board and a universal main control development board for control, and a high-power DC power supply as the load-end power supply. The digital output port of the universal main control development board can produce an analog potential output effect of approximately 0-5V. In use, up to 8 SMA springs can be connected in series to each current controller circuit, and the corresponding digital output pins in the universal main control development board are selected to connect to the control end pins of the current controller circuit, and the positive and negative poles of the DC power supply used to drive the SMA spring are connected to the load power supply end of the current controller circuit to complete the connection of the controller. During the control process, by defining each digital output level (range 0-255) in the control code, the power on and off of each SMA spring and the current size can be controlled.

[0068] like Figure 1 , showing a schematic diagram of a multi-motion mode soft robot system. The system includes a shape memory alloy (SMA) drive module, a foot directional friction structure, a control circuit, and a motion mode switching module. The SMA drive module realizes the phase change of the SMA by heating it with electricity, thereby realizing the movement of the robot. The foot directional friction structure can adjust the friction distribution according to the movement direction and needs of the robot to achieve directional movement. The control circuit realizes the switching of multiple motion modes through a carefully designed SMA power-on time sequence.

[0069] like Figure 2, showing a schematic diagram of a soft robot system performing crawling motion. During crawling, the elastic skeleton does not need to cross the equilibrium point in the bistable state, but only needs to bend back and forth on one side. Therefore, the time difference Δt between the start of power-on of the SMA springs on both sides can be appropriately shortened, and the robot can achieve alternating bending of the front and rear feet, thereby achieving crawling motion.

[0070] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0071] Those skilled in the art know that, in addition to implementing the system, device and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps. Therefore, the system, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing the method and structures within the hardware component.

[0072] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A multi-motion mode micro soft robot driven by shape memory alloy, characterized in that: include: Elastic skeleton, SMA actuator and passive friction device at the bottom of the mechanism; The SMA driver is fixed on the front and back sides of the elastic frame; The passive friction device at the bottom of the mechanism is fixed to the end of the elastic frame; The elastic skeleton is the main body of the robot mechanism, and is used to provide pre-deformation of the SMA actuator at room temperature, and utilize elastic potential energy to restore the SMA actuator in a relaxed state to the initial pre-deformed state; The SMA actuator is used to axially compress under external electric field heating, and the generated tension causes the elastic skeleton connected thereto to be unidirectionally bent and deformed, thereby generating a propulsion force to drive the robot to achieve a preset motion mode; The passive friction device at the bottom of the mechanism is used to realize a unidirectional friction structure, realize the directional crawling of the robot, and enable the basic movement ability of the robot.

2. The shape memory alloy driven multi-motion mode micro soft robot according to claim 1, characterized in that: The SMA actuator is an orthodontic tension spring.

3. The shape memory alloy driven multi-motion mode micro soft robot according to claim 1, characterized in that: Also included are auxiliary materials: power cord and thermal insulation tape; The power line is connected to an external power source and the SMA driver to provide a working current for the SMA driver; The heat-insulating adhesive tape is adhered to the front and back surfaces of the elastic frame.

4. The shape memory alloy driven multi-motion mode micro soft robot according to claim 1, characterized in that: The elastic skeleton selection requirements include two factors: one is to provide sufficient support force to achieve the desired pre-deformation degree of the SMA actuator, and the other is to provide sufficiently large elastic potential energy as a restoring force to ensure that the SMA actuator switches between the extension and contraction states.

5. The shape memory alloy driven multi-motion mode micro soft robot according to claim 1, characterized in that: The SMA actuator selection requirements include: considering the responsiveness to temperature, deformation rate and maximum load; considering that when the robot is performing crawling and jumping movements, the SMA actuator needs to generate a large enough pulling force so that the bending degree of the elastic skeleton can meet the task requirements.

6. The shape memory alloy driven multi-motion mode micro soft robot according to claim 3, characterized in that: The selection of the power cord includes two factors: one is to provide the SMA driver with a sufficiently large working current stably, and the other is to use lightweight wire without affecting the movement of the robot.

7. The shape memory alloy driven multi-motion mode micro soft robot according to claim 3, characterized in that: The heat-insulating adhesive tape adopts double-layer heat-insulating adhesive tape as the heat-insulating layer, the adhesive surfaces are adhered to each other, and the non-adhesive surfaces face outwards.

8. The shape memory alloy driven multi-motion mode micro soft robot according to any one of claims 1 to 7, characterized in that: The assembly process is: Step S1: integrating the selected materials; Step S2: Based on energy conservation, the robot motion modeling and analysis are performed; Step S3: designing a bistable structure to expand the jumping function of the mechanism; Step S4: According to the driving mechanism of the SMA actuator, a control method of connecting a switch circuit in series with the SMA actuator is adopted to achieve effective control of the temperature of the SMA actuator.

9. The shape memory alloy driven multi-motion mode micro soft robot according to claim 8, characterized in that: The step S2 comprises: Assuming the initial bending angle of the elastic skeleton is 0, the strain energy stored in the plate due to bending relative to θ is: The tensile strain energy in the SMA actuator is: Where, under different conditions of the corresponding bending angle θ, when θ<0, it means that the elastic skeleton is bent downward; when θ>0, it means that the elastic skeleton is bent upward; in each, the first term corresponds to the strain energy of the SMA actuator placed on the lower side of the elastic skeleton; the second term corresponds to the strain energy of the SMA actuator on the upper side of the elastic skeleton; assuming that the deformation of the SMA actuator is linearly related to the temperature, L max , L0 represent the stretched length and initial length of the SMA actuator, respectively; k1 and k2 represent the SMA spring stiffness; The total potential energy of the system during bending is: U t =U SMA +U bend .

10. The shape memory alloy driven multi-motion mode micro soft robot according to claim 8, characterized in that: The step S3 includes: designing the initial state of the mechanism to be a straight line, combining energy distribution and stretching potential energy to make the total energy in the mechanism symmetrically distributed, heating the SMA actuators on both sides, and increasing the stiffness k of the SMA actuators, so that the total energy of the system has two symmetrical local minimum points on the left and right sides, that is, two stable states. In this way, the SMA actuator stores / releases energy during the bending process, generates instantaneous dynamics after the energy peak, and drives the robot to jump and climb over as a whole.

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