Linear displacement actuator based on single-pass shape memory alloy

Abstract

This invention discloses a linear displacement actuator based on a single-pass shape memory alloy, comprising a housing, within which a movable cam is disposed. An auxiliary spring and a shape memory alloy spring are respectively disposed on opposite sides of the movable cam. Electrode plate I and electrode plate II are respectively disposed at both ends of the shape memory alloy spring. An output rod is connected to the movable cam via rollers. This invention solves the problem of difficulty in achieving high-precision deformation control in existing actuators due to the nonlinear deformation characteristics of shape memory alloys.

Description

Technical Field

[0001] This invention belongs to the field of shape memory alloy actuator technology, and relates to a linear linear displacement actuator based on a single-pass shape memory alloy. Background Technology

[0002] Shape memory alloys are characterized by their shape memory effect. The one-way shape memory effect means that when a material is deformed under external force below its martensitic transformation end temperature, if heated above the austenitic transformation temperature, it will undergo an austenitic transformation and recover its original shape. During this transformation, shape memory alloys can generate significant recoverable deformation and restoring stress. Based on this characteristic, shape memory alloys are very suitable for manufacturing actuators. However, the deformation of shape memory alloys during the phase transformation process is non-linear with temperature, which increases the difficulty of precisely controlling the deformation of shape memory alloys. Summary of the Invention

[0003] The purpose of this invention is to provide a linear displacement actuator based on a single-pass shape memory alloy, which solves the problem of difficulty in accurately controlling deformation caused by the nonlinear deformation law of shape memory alloy in existing actuators.

[0004] The technical solution adopted in this invention is a linear displacement actuator based on a single-pass shape memory alloy, including a housing, a movable cam inside the housing, an auxiliary spring and a shape memory alloy spring on opposite sides of the movable cam, an electrode plate I and an electrode plate II at both ends of the shape memory alloy spring, and an output rod connected to the movable cam via rollers.

[0005] The invention is further characterized by:

[0006] Electrode I is located on the inner wall of one end of the housing, and electrode II is located at one end of the moving cam. One end of the shape memory alloy spring is connected to the housing through electrode I, and the other end of the shape memory alloy spring is connected to the moving cam through electrode II.

[0007] A hole II is provided at the center of one end of the outer casing. Hole II and electrode I are located at the same end of the outer casing. The wire enters through hole II and is connected to electrode I and electrode II to conduct electricity.

[0008] A hole I is provided at the top center of the housing. One end of the output rod extends out of the housing through hole I, and the other end of the output rod is connected to the roller.

[0009] The bottom of the output rod is provided with hole III; the roller includes a roller wheel, and a roller pin is provided at the center of the roller wheel. The roller pin is inserted into hole III at the bottom of the output rod to connect with the output rod.

[0010] The surface of the movable cam is provided with a rolling groove, which has a wave-shaped structure.

[0011] The design method for the rolling groove is as follows:

[0012] Step 1: Measure the deformation u of the shape memory alloy spring during the austenitic phase transformation stage at different temperatures T;

[0013] Step 2: Let the deformation amount u of the shape memory alloy spring obtained in Step 1 be the independent variable and the temperature T be the dependent variable, and establish the temperature function for the austenite phase transformation stage.

[0014] Step 3: Substitute the temperature function of the austenitic phase transformation stage into the linear output function of the actuator to obtain the correspondence between the deformation amount u of the shape memory alloy spring and the output displacement of the actuator during the phase transformation stage. Using the deformation amount u of the shape memory alloy spring as the x-axis coordinate and the output displacement of the actuator as the y-axis coordinate, obtain the profile equation of the rolling groove in the two-dimensional coordinate system.

[0015] Shape memory alloy springs are nickel-titanium alloy springs that possess a single-pass shape memory effect.

[0016] The beneficial effects of this invention are as follows:

[0017] 1) The driving element used in this invention is a nickel-titanium alloy spring with a single-pass shape memory effect. Compared with shape memory alloy wire, shape memory alloy spring has the characteristics of large driving force and large deformation range. Furthermore, it is controlled by heating through energization, which gives the actuator the advantages of large output displacement and convenient control.

[0018] 2) This invention converts the nonlinear deformation law of shape memory alloy into linear linear displacement output, improves the resolution of deformation controlled by temperature, and thus improves the control accuracy of shape memory alloy actuator and reduces the control difficulty.

[0019] 3) This invention uses both a shape memory alloy spring and an auxiliary spring to clamp the slider, which can control the output while also having a self-locking function, ensuring the stability of the output displacement. Furthermore, the auxiliary spring restores the shape of the shape memory alloy spring, overcoming the shortcoming of the single-pass memory effect that cannot automatically recover the initial state, and can output the required displacement arbitrarily multiple times. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the linear displacement actuator based on a single-pass shape memory alloy according to the present invention.

[0021] Figure 2 This is a schematic diagram of the housing of the linear displacement actuator based on a single-pass shape memory alloy according to the present invention;

[0022] Figure 3 This is a schematic diagram of the moving cam structure of the linear linear displacement actuator based on a single-pass shape memory alloy according to the present invention;

[0023] Figure 4 This is a schematic diagram of the output rod of the linear linear displacement actuator based on a single-pass shape memory alloy according to the present invention;

[0024] Figure 5 This is a schematic diagram of the structure of the linear displacement actuator roller based on a single-pass shape memory alloy according to the present invention;

[0025] Figure 6 This is a schematic diagram of the shape memory alloy spring of the linear linear displacement actuator based on single-pass shape memory alloy of the present invention.

[0026] In the figure, 1. housing, 2. moving cam, 3. output rod, 4. roller, 5. auxiliary spring, 6. shape memory alloy spring, 11. hole I, 12. hole II, 13. electrode plate I, 21. rolling groove, 22. electrode plate II, 31. hole III, 41. roller pin, 42. roller wheel. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] This invention is based on a linear displacement actuator using a single-pass shape memory alloy, such as... Figure 1 As shown, it includes an outer shell 1, which is a closed cavity structure, such as... Figure 2 As shown, an electrode plate I13 is provided on one side of the inner wall of the outer shell 1, and a hole I11 is provided on the top of the outer shell 1. The output rod 3 extends out of the outer shell 1 through the hole I11 to output linear displacement. The moving cam 2 is provided in the inner cavity of the outer shell 1. The size of the moving cam 2 matches the inner cavity of the outer shell 1, so that the moving cam 2 can only move back and forth in the inner cavity of the outer shell 1 in a direction perpendicular to the output rod 3. A roller 4 is provided at the lower end of the output rod 3. A shape memory alloy spring 6 and an auxiliary spring 5 are respectively provided on both sides of the moving cam 2 in the inner cavity of the outer shell 1.

[0030] Example 2

[0031] like Figure 3 As shown, the surface of the movable cam 2 is provided with a rolling groove 21, and the roller 4 is embedded in the rolling groove 21 on the surface of the movable cam 2, allowing the roller 4 to move within the rolling groove 21. An electrode plate II 22 is provided at one end of the bottom of the movable cam 2. The electrode plates I 13 and II 22 are identical in size and shape.

[0032] like Figure 4 As shown, the bottom of the output rod 3 is provided with hole III31. Figure 5 As shown, the roller 4 consists of a roller pin 41 and a roller wheel 42. The roller pin 41 is inserted into the hole III at the bottom of the output rod 3 to connect with the output rod 3. The roller wheel 42 is embedded in the rolling groove 21 on the side of the moving cam 2 and can only move in the rolling groove 21. Since the position of the output rod 3 is constrained by the hole I11 on the housing 1, the position of the roller 4 is determined by the moving cam 2 and the output rod 3 together and does not require additional fixing. The roller 4 itself can only move up and down with the output rod 3.

[0033] Example 3

[0034] A hole II12 is provided at the center of one end of the outer casing 1. The hole II12 and the electrode plate I13 are located at the same end of the outer casing 1. The wire enters through the hole II12 and is connected to the electrode plate I13 and the electrode plate II22 for energizing.

[0035] An auxiliary spring 5 is located on the right side of the moving cam 2 inside the outer shell 1. The two ends of the auxiliary spring 5 are in contact with the moving cam 2 and the outer shell 1, respectively. A shape memory alloy spring 6 is located on the left side of the moving cam 2 inside the outer shell 1. The two ends of the shape memory alloy spring 6 are in contact with electrode plate I13 and electrode plate II22, respectively, to achieve connection with an external power source.

[0036] Auxiliary spring 5 is a common pure steel spring, such as Figure 6 As shown, the shape memory alloy spring 6 is a nickel-titanium alloy spring with a single-pass shape memory effect. In the initial state, the auxiliary spring 5 is in a fully extended state, and the shape memory alloy spring 6 is in a fully contracted state (the shape memory alloy is in the martensitic phase). The roller 4 is located at the rightmost end of the rolling groove 21 on the moving cam 2.

[0037] The motion law of the output rod 3 is determined by the motion law of the roller 4 in the rolling groove 21. The motion law of the roller 4 is jointly determined by the deformation law of the shape memory alloy spring 6 and the curve shape (profile) of the rolling groove 21. This actuator realizes the transformation of the nonlinear deformation law of the shape memory alloy spring 6 during the austenitic phase transformation into the linear displacement of the output rod 3 by designing the curve shape of the rolling groove 21. The specific steps for designing the profile of the rolling groove 21 are as follows:

[0038] Step 1: Based on the constitutive relation of the shape memory alloy spring 6, or by experimentally measuring the temperature-corresponding deformation data of the shape memory alloy spring 6, obtain the temperature-deformation curve u=f(T), where u is the deformation of the shape memory alloy spring 6 and T is the temperature;

[0039] Step 2: In order to convert the deformation of the shape memory alloy spring 6 into the x-axis coordinate of the rolling groove 21, the independent and dependent variables of the temperature-deformation curve u=f(T) are swapped, and the deformation u is used to obtain the temperature T, thus obtaining the deformation-temperature function T=g(u).

[0040] Step 3: Since the actuator output is linear, there is a displacement function d = k·T, where d is the actuator output displacement, k is a proportionality coefficient representing the proportional relationship between temperature and output displacement, and the value of k determines the actuator's operating range, which is determined by actual needs. The deformation of the shape memory alloy spring 6 is used as the x-axis coordinate of the profile. Substituting the deformation-temperature function T = g(u) into the displacement function d = k·T, we get d = k·g(u), which is the profile equation of the rolling groove. The deformation u of the shape memory alloy spring 6 is the x-axis coordinate, and the actuator output displacement d is the y-axis coordinate.

[0041] The working process of the linear displacement actuator based on single-pass shape memory alloy of this invention is divided into two stages: output stage and reset stage, specifically:

[0042] During the output phase, the output rod 3 extends outward from the housing 1. The control method is that the electrode plate I13 and electrode plate II22 are in contact with the two ends of the shape memory alloy spring 6, and the shape memory alloy spring 6 is energized to raise its temperature above the austenitic phase transformation start temperature, so that the shape memory alloy spring 6 undergoes an austenitic phase transformation and thus produces elongation deformation. When the shape memory alloy spring 6 elongates, it pushes the moving cam 2 to move towards the side where the auxiliary spring 5 is located, squeezing the auxiliary spring 5. At this time, the roller 4 moves relative to the rolling groove 21 due to the movement of the moving cam 2, thereby driving the output rod 3 to extend outward.

[0043] During the reset phase, the output rod 3 retracts from the outer shell 1 inward to its initial position. The control method is as follows: the electrode plates I13 and II22 are in contact with both ends of the shape memory alloy spring 6, the external power is turned off to cool the shape memory alloy spring 6 to below the martensitic initiation temperature, and the shape memory alloy spring 6 stops generating driving force after undergoing martensitic phase transformation. Therefore, the auxiliary spring 5, which was compressed during the output phase, begins to rebound. After the auxiliary spring 5 rebounds and extends, it pushes the moving cam 2 to move towards the side where the shape memory alloy spring 6 is located, squeezing the shape memory alloy spring 6 to contract it and generate martensitic phase transformation. At this time, the roller 4 moves relative to the rolling groove 21 due to the movement of the moving cam 2, thereby driving the output rod 3 to retract inward.

[0044] Both the output and reset phases use the initial state as the reference point. Only the output phase involves linear motion. During the heating phase (austenitic phase transformation phase), the temperature of the shape memory alloy spring 6 can be controlled by adjusting the current of the external power supply. Therefore, the value of the actuator's output displacement can be precisely customized by controlling the temperature of the shape memory alloy spring 6. After each output, the actuator state is reset to prepare for the next output. It should be noted that during the extension phase, the shape memory alloy spring 6 compresses the auxiliary spring 5. Therefore, during the reset phase, the auxiliary spring 5 generates a driving force, causing the shape memory alloy spring 6 to contract back to its initial state. This provides the shape memory alloy spring 6 with the prerequisites for a single-pass shape memory effect. Therefore, this actuator can complete any number of displacement outputs.

[0045] This invention is based on a linear displacement actuator of a single-pass shape memory alloy, which can transform the nonlinear deformation law of the shape memory alloy into a linear displacement output mode. This greatly increases the control resolution and control accuracy of the actuation mode based on shape memory alloy, reduces the control difficulty, and also has the characteristics of large driving force, large deformation range, and reusability.

Claims

1. A linear displacement actuator based on a single-pass shape memory alloy, characterized in that: Includes a housing (1), inside which is a movable cam (2), on opposite sides of the movable cam (2) are an auxiliary spring (5) and a shape memory alloy spring (6), at both ends of the shape memory alloy spring (6) are an electrode plate I (13) and an electrode plate II (22), and the movable cam (2) is connected to an output rod (3) via a roller (4); The electrode plate I (13) is located on the inner wall of one end of the housing (1), the electrode plate II (22) is located at one end of the moving cam (2), one end of the shape memory alloy spring (6) is connected to the housing (1) through the electrode plate I (13), and the other end of the shape memory alloy spring (6) is connected to the moving cam (2) through the electrode plate II (22). A hole II (12) is provided at the center of one end of the housing (1). The hole II (12) and the electrode plate I (13) are located at the same end of the housing (1). The wire enters through the hole II (12) and connects to the electrode plate I (13) and the electrode plate II (22) for energizing. The housing (1) has a hole I (11) at the top center, one end of the output rod (3) extends out of the housing (1) through the hole I (11), and the other end of the output rod (3) is connected to the roller (4); The bottom of the output rod (3) is provided with hole III (31); the roller (4) includes roller wheel (42), and a roller pin (41) is provided at the center of the roller wheel (42). The roller pin (41) is inserted into hole III (31) at the bottom of the output rod (3) to connect with the output rod (3); The surface of the movable cam (2) is provided with a rolling groove (21), which has a wave-shaped structure. The design method of the rolling groove (21) is as follows: Step 1: Measure the deformation of the shape memory alloy spring (6) during the austenitic phase transformation stage at different temperatures T. ; Step 2, let the deformation of the shape memory alloy spring (6) obtained in Step 1 be... With temperature T as the dependent variable, establish a temperature function for the austenitic phase transformation stage. Step 3: Substitute the temperature function of the austenitic phase transformation stage into the linear output function of the actuator to obtain the deformation of the shape memory alloy spring (6) during the phase transformation stage. The correspondence between the actuator output displacement and the deformation of the shape memory alloy spring (6) is expressed as follows. for The axis coordinates and the actuator output displacement are Coordinates are used to obtain the profile equation of the rolling groove (21) in the two-dimensional coordinate system; The shape memory alloy spring (6) is a nickel-titanium alloy spring with a single-pass shape memory effect.

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