A low-melting-point alloy variable-stiffness temperature control method and structure and soft manipulator

Abstract

The present invention discloses a low-melting-point alloy variable stiffness temperature control method and structure, and a soft manipulator, comprising a mounting frame and a plurality of low-melting-point alloy variable stiffness temperature control structures connected to the mounting frame; the low-melting-point alloy variable stiffness temperature control structure comprises a pneumatic soft drive and a variable stiffness layer fixedly attached to the inner / outer surface of the pneumatic soft drive, wherein a low-melting-point alloy is encapsulated in the variable stiffness layer; the temperature of the low-melting-point alloy is controlled within a range of ±0.5°C of its melting point, and the low-melting-point alloy is heated or cooled to absorb or release the energy required for phase change latent heat, thereby achieving rapid melting and solidification of the low-melting-point alloy. The present invention addresses the shortcomings of the mainstream interference variable stiffness method of soft mechanical structures, which has low stiffness and slow response of the low-melting-point alloy variable stiffness method. The alloy only needs to absorb or release latent heat and increase or decrease the heat of the alloy by one degree to complete the phase change, achieving stepless stiffness adjustment that cannot be achieved by existing methods.

Description

Technical Field

[0001] The present invention relates to the technical field of soft robots, and more particularly to a low-melting-point alloy variable-rigidity temperature control method and structure and a soft robot arm. Background Art

[0002] Soft materials give soft robots a high degree of compliance, flexibility, and safety, but they also significantly reduce their rigidity, resulting in problems such as low load, low output force, and low stability. Therefore, how to adjust the rigidity of soft robots to achieve a rigid-flexible transition and improve their performance, allowing them to undertake more tasks, is a key area of ​​soft robotics research.

[0003] Existing soft robot stiffness changing methods are mainly interference, antagonism, smart materials, phase change, etc. Interference is currently a widely used stiffness changing method, which squeezes particles, layers, wires and other materials together by extracting negative pressure to increase friction and achieve overall stiffness improvement. For example, the applicant has applied for invention patents with publication numbers CN109249385A, CN111055299A and CN111941462A, but this method still has the problems of small stiffness adjustment range and low adjustable stiffness. Antagonism is a stiffness adjustment achieved by utilizing the antagonistic effect of different movements in the soft robot through a special structural arrangement. It occupies a large volume and is a less used stiffness changing method. Smart materials are usually activated by electric fields or magnetic fields, which can achieve a stiffness adjustment method from a free or loose state to a regularly arranged or taut state, and have high requirements for external conditions. Phase change is a method of changing stiffness by utilizing the heat absorption and release of materials to achieve the conversion between solid and liquid phases to achieve stiffness transformation. Among them, phase change low-melting-point alloys have the highest stiffness adjustment ability, but there are problems such as the long phase change process and the inability to freely adjust the stiffness.

[0004] Therefore, if the time required for phase change can be shortened in some way and the problem that stiffness can only be converted between low stiffness in the liquid phase and high stiffness in the solid phase can be solved, then low-melting-point alloys can effectively solve the stiffness problem of robots, which is of great significance for promoting the research and application of soft robots. Summary of the Invention

[0005] In view of this, the present invention provides a low-melting-point alloy variable stiffness temperature control method and structure and a soft manipulator, aiming to solve the above technical problems.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for controlling the stiffness change temperature of a low-melting-point alloy is disclosed. The temperature of the low-melting-point alloy is controlled within the range of ±0.5°C of its melting point. The low-melting-point alloy is heated or cooled so as to absorb or release the energy required for phase change latent heat, thereby achieving rapid melting and solidification of the low-melting-point alloy.

[0008] Through the above technical solution, when the alloy state needs to be changed, the present invention only needs to reduce the efficiency of the alloy cooling system to allow the alloy to absorb the latent heat required for the first-stage phase transition, transforming from a solid phase to a liquid phase; or increase the efficiency of the alloy's peripheral cooling device to release the heat equivalent to the first-stage phase transition latent heat within the alloy through the cooling device, transforming from a liquid phase to a solid phase. The temperature and pressure remain unchanged throughout the phase transition process, and only heat is absorbed or released during the phase transition. Improving heating and cooling efficiency can effectively reduce reaction time.

[0009] Preferably, in the above-mentioned method for controlling the temperature change of the low-melting-point alloy stiffness, the amount of heat provided by heating the low-melting-point alloy and the amount of heat removed by water cooling is adjusted to control the amount of latent heat absorbed or released by the low-melting-point alloy after reaching the melting point, thereby achieving control over the ratio of the solid phase and the liquid phase of the low-melting-point alloy in the latent heat stage. The solid-liquid ratio of the alloy is constantly decreasing or increasing. As the solid phase ratio of the alloy decreases, the stiffness of the alloy continues to decrease. Therefore, by adjusting the amount of heat provided by heating the alloy and the amount of heat removed by water cooling, the amount of heat absorbed or released by the alloy after reaching the melting point is controlled to achieve control over the ratio of the solid phase and the liquid phase of the alloy in the latent heat stage, thereby achieving infinite regulation of the stiffness.

[0010] The present invention also provides a low-melting-point alloy variable-stiffness temperature control structure, comprising a pneumatic soft drive and a variable-stiffness layer fixed to the inner / outer surface of the pneumatic soft drive, wherein the variable-stiffness layer encapsulates a low-melting-point alloy, and the low-melting-point alloy is rapidly melted and solidified by the above-mentioned low-melting-point alloy variable-stiffness temperature control method.

[0011] Through the above technical solution, the present invention addresses the low stiffness of the mainstream interference stiffness change method of soft mechanical structures and the slow response of the low-melting-point alloy stiffness change method, and proposes a low-melting-point alloy stiffness change temperature control structure based on heat control. This control structure is based on the characteristic that the phase change process of eutectic low-melting-point alloys needs to absorb or release latent heat after reaching the melting point. By controlling the heat supply and heat consumption, the temperature of the alloy is maintained at 0.5 degrees Celsius below the melting point (solid phase) or above the melting point (liquid phase). At this time, the alloy only needs to absorb or release latent heat and increase or decrease the heat of the alloy by one degree to complete the phase change. Based on the heat control of the low-melting-point alloy phase change, the solid and liquid phase ratio of the alloy can also be kept unchanged during the latent heat stage, thereby realizing stepless stiffness adjustment that cannot be achieved by existing methods.

[0012] Preferably, in the aforementioned low-melting-point alloy variable-stiffness temperature control structure, the pneumatic soft actuator is a closed half-corrugated expansion tube structure, one end of which has an air tube connected to its inner cavity. When air is inflated or deflated through the air tube, the half-corrugated expansion tube structure can bend and straighten.

[0013] Preferably, in the above-mentioned low-melting-point alloy variable-stiffness temperature control structure, the variable-stiffness layer includes a silicone wrapping layer, which is bonded and fixed to the inner and outer surfaces of the pneumatic soft actuator. Two shaped chambers are formed inside the silicone wrapping layer. The outer shaped chamber encapsulates the low-melting-point alloy and the heating wire, and the inner shaped chamber is provided with a cooling water flow channel. The low-melting-point alloy and the heating wire are encapsulated in the same shaped chamber, the cooling water flow channel is in a separate shaped chamber, and the silicone wrapping layer wraps all the structures together.

[0014] Preferably, in the aforementioned low-melting-point alloy variable stiffness temperature control structure, the low-melting-point alloy is heated by Joule heating, using copper wire, carbon fiber wire, or the like as a heating element, and the heating power is maintained stable by adjusting the voltage; and the low-melting-point alloy is cooled by water convection cooling, and the water cooling efficiency is controlled by controlling the water flow rate and cooling water temperature. The overall heating power (heat supply) of the alloy remains unchanged, and the cooling (heat consumption) efficiency is changed to control the overall heat within the alloy.

[0015] Preferably, in the above-mentioned low-melting-point alloy variable stiffness temperature control structure, the temperature, internal heat and phase change of the low-melting-point alloy are controlled by adjusting the heating power of the low-melting-point alloy and the temperature and flow rate of the cooling liquid in the cooling water flow pipe; and the solid-liquid ratio of the low-melting-point alloy is controlled by adjusting the supply and loss of heat, thereby exhibiting different stiffnesses.

[0016] The present invention also provides a soft manipulator, comprising a mounting frame, and a plurality of the above-mentioned low-melting-point alloy variable-rigidity temperature control structures connected to the mounting frame.

[0017] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a low-melting-point alloy variable stiffness temperature control method and structure and a soft manipulator, which have the following beneficial effects:

[0018] 1. The present invention is different from the existing method of changing the stiffness of low-melting-point alloys. It utilizes the characteristic that when the eutectic alloy reaches the melting point during the melting process, it needs to absorb a certain amount of heat to completely melt. The alloy temperature is maintained at a state slightly lower than or just reaching the melting point. The alloy can be melted by heating for a period of time. Similarly, rapid cooling and solidification can be achieved, which can greatly reduce the time required for the phase change of the low-melting-point alloy.

[0019] 2. The present invention is different from the existing low-melting-point alloy stiffness changing method. It utilizes the characteristics that eutectic alloys reach the melting point when melting or solidifying, and need to absorb or release a certain amount of heat to melt or solidify. The alloy temperature is maintained at the melting point temperature, and the heat absorbed or released by the alloy is controlled to achieve stepless regulation of stiffness.

[0020] 3. The present invention is different from the existing variable stiffness clamps. The variable stiffness method of low melting point alloy not only effectively achieves higher stiffness adjustment, but also the influence of the alloy integrated inside on the movement of the clamp in liquid state is far less than that of the variable stiffness method with interference from particles, layer lines, etc.

[0021] 4. The variable stiffness method of the present invention is applicable to all soft robots that require stiffness adjustment to improve performance, especially soft robotic arms that need to perform load operations and soft continuum robots with a large workspace. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0023] Figure 1 The accompanying drawing is a melting curve (time-temperature) of the low melting point alloy provided by the present invention;

[0024] Figure 2 The accompanying drawing shows the change in the solid-liquid ratio of the low-melting-point alloy provided by the present invention during the latent heat stage;

[0025] Figure 3 The accompanying drawing is a schematic diagram of a low-melting-point alloy variable stiffness temperature control structure provided by the present invention;

[0026] Figure 4 The accompanying drawing is a schematic diagram of the internal structure of the low-melting-point alloy variable stiffness temperature control structure provided by the present invention;

[0027] Figure 5 The accompanying drawing shows that the stiffness of the variable stiffness layer provided by the present invention is reduced by reducing the solid ratio;

[0028] Figure 6 The accompanying drawings illustrate the working process of the low-melting-point alloy variable stiffness temperature control structure provided by the present invention;

[0029] Figure 7 The accompanying figure shows the state of the soft manipulator provided by the present invention before grasping;

[0030] Figure 8 The accompanying figure shows the state in which the soft manipulator provided by the present invention has completed grasping.

[0031] in:

[0032] 1-Pneumatic soft drive;

[0033] 11-trachea;

[0034] 2-variable stiffness layer;

[0035] 21-Silica gel wrapping layer; 22-U-shaped chamber; 23-Heating wire; 24-Cooling water flow pipe;

[0036] 3-Mounting frame;

[0037] 4- The object being grasped. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Example 1:

[0040] See attached Figure 1 and attached Figure 2 The embodiment of the present invention discloses a method for controlling the temperature of a low-melting-point alloy to change its stiffness. The core of the method is to control the temperature of the low-melting-point alloy to be 0.5°C below the melting point (solid phase) or 0.5°C above the melting point (liquid phase) by continuous intermittent heating and cooling. Figure 1 When the alloy's state needs to be changed, the efficiency of the alloy's cooling system can be reduced to allow the alloy to absorb the latent heat required for the first-order phase transition, transforming from solid to liquid. Alternatively, the efficiency of the alloy's peripheral cooling system can be increased to release the heat within the alloy equivalent to the first-order phase transition latent heat through the cooling system, transforming from liquid to solid. The temperature and pressure remain constant throughout the phase transition, and only heat is absorbed or released during the phase transition. Improving heating and cooling efficiency can effectively reduce reaction time.

[0041] In the process of absorbing and releasing heat by low melting point alloys, such as Figure 2 As shown in the figure, the solid-liquid ratio of the alloy is constantly decreasing or increasing. As the solid phase ratio of the alloy decreases, the stiffness of the alloy continues to decrease. Therefore, by adjusting the heat provided by alloy heating and the heat taken away by water cooling, the heat absorbed or released by the alloy after reaching the melting point is controlled, thereby realizing the ratio control of the solid and liquid phases of the alloy in the latent heat stage, so as to achieve infinite regulation of stiffness.

[0042] Example 2:

[0043] See attached Figure 3 , the embodiment of the present invention discloses a low melting point alloy variable stiffness temperature control structure, including two layers, such as the upper and lower layers. Figure 3 As shown, the upper layer is a soft actuator made of silicone with a fast pneumatic grid structure for realizing bending function, and the lower layer is a low-melting-point alloy variable stiffness layer encapsulated in silicone for realizing stiffness adjustment.

[0044] The variable stiffness layer 2 includes three parts: a low melting point alloy, a heating wire 23 and a cooling water flow pipe 24. Figure 4 As shown, the low-melting-point alloy and the heating wire 23 are encapsulated within the same shaped chamber 22. The cooling water flow channel 24 occupies a separate shaped chamber 22, and the entire structure is enclosed by a silicone sheath 21. When powered, the heating wire 23 transfers heat to the low-melting-point alloy via conduction, using the principle of Joule heating, causing it to melt. Water or coolant flows through the cooling water flow channel 24, dissipating the heat from the alloy by convection. By adjusting the alloy heating power and the temperature and flow rate of the cooling liquid in the cooling water flow channel 24, the temperature of the low-melting-point alloy and the occurrence of phase changes can be controlled.

[0045] By adjusting the power of alloy heating and the temperature and flow rate of the cooling liquid in the cooling water flow pipe 24, the temperature, internal heat and phase change of the low melting point alloy can be controlled. Figure 5 As shown, by adjusting the supply and loss of heat, the solid-liquid ratio of the alloy in the variable stiffness layer 2 can be controlled, thereby exhibiting different stiffnesses.

[0046] The low melting point alloy in the variable stiffness layer 2 is in the liquid phase under normal conditions, such as Figure 6 As shown, the manipulator can generate bending motion at will. When higher stiffness is required, the alloy temperature drops to the melting point and releases latent heat, the state changes from liquid to solid, and the stiffness of the drive increases.

[0047] Example 3:

[0048] See attached Figure 7 and attached Figure 8 An embodiment of the present invention discloses a soft manipulator, including a mounting frame 3, and multiple low-melting-point alloy variable-stiffness temperature control structures of embodiment 2 connected to the mounting frame 3, and the multiple low-melting-point alloy variable-stiffness temperature control structures are evenly arranged in a ring shape on the outside of the mounting frame 3.

[0049] The soft manipulator of this embodiment is assembled from four low-melting-point alloy variable-rigidity temperature control structures with exactly the same structure, and can achieve stable grasping of objects of different shapes and weights within the grasping range.

[0050] Under normal conditions, the alloy in the variable stiffness layer 2 of the low melting point alloy variable stiffness temperature control structure is in liquid phase. At this time, the manipulator is in a free state. The difference between the heat supplied by the heating wire 23 and the internal heat taken away by the cooling liquid maintains the alloy heat at 0.5 degrees Celsius above the melting point. Figure 7 As shown, the manipulator positions the grasped object 4, and its four low melting point alloy variable stiffness temperature control structures are in a vertical state, and gas is filled into the four pneumatic soft actuators 1 to wrap the object, as shown in FIG. Figure 8 As shown in the figure, after the manipulator fully secures the robot, a phase transition and stiffness change begins. Without changing the manipulator's heating power or heat supply, the temperature of the cooling liquid in the soft gripper is reduced or its flow rate is increased, increasing the amount of heat removed from the alloy. Once the temperature drops to the melting point, further cooling is performed to release all the latent heat in the alloy. The temperature is then further lowered to 0.5°C below the melting point. At this point, the cooling efficiency is readjusted to maintain the alloy temperature at 0.5°C below the melting point, and the soft gripper enters a high-stiffness state.

[0051] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0052] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low melting point alloy variable stiffness temperature control structure, characterized in that: The invention comprises a pneumatic soft drive (1), and a variable stiffness layer (2) fixedly attached to the inner / outer surface of the pneumatic soft drive (1), wherein a low melting point alloy is encapsulated in the variable stiffness layer (2), and the temperature of the low melting point alloy is controlled within the range of ±0.5°C of its melting point temperature, and the low melting point alloy absorbs or releases the energy required for phase change latent heat by heating or cooling, thereby achieving rapid melting and solidification of the low melting point alloy; By adjusting the heat provided by heating the low-melting-point alloy and the heat taken away by water cooling, the latent heat absorbed or released by the low-melting-point alloy after reaching the melting point is controlled, thereby achieving control over the ratio of the solid phase and the liquid phase of the low-melting-point alloy in the latent heat stage; The low melting point alloy is heated by Joule heating; the low melting point alloy is cooled by water convection cooling; The variable stiffness layer (2) includes a silicone wrapping layer (21), the silicone wrapping layer (21) is fixedly attached to the inner and outer surfaces of the pneumatic soft actuator (1), and two shaped chambers (22) are formed inside the silicone wrapping layer (21), a low melting point alloy and a heating wire (23) are encapsulated in the outer shaped chamber (22), and a cooling water flow pipe (24) is provided in the inner shaped chamber (22); By adjusting the power of heating the low-melting-point alloy and the temperature and flow rate of the cooling liquid in the cooling water flow pipe (24), the temperature of the low-melting-point alloy and the occurrence of internal heat and phase change are controlled; by adjusting the supply and loss of heat, the solid-liquid ratio of the low-melting-point alloy is controlled, thereby showing different stiffness.

2. A low melting point alloy variable stiffness temperature control structure according to claim 1, characterized in that: The pneumatic soft driver (1) is a closed half corrugated expansion tube structure, and one end of the pneumatic soft driver (1) has an air tube (11) connected to its inner cavity.

3. A soft manipulator, characterized in that: The invention comprises a mounting frame (3), and a plurality of low-melting-point alloy variable-rigidity temperature control structures according to any one of claims 1 to 2 connected to the mounting frame (3).

4. A soft manipulator according to claim 3, characterized in that: A plurality of low melting point alloy variable stiffness temperature control structures are evenly arranged in a ring shape on the outside of the mounting frame (3).

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