Length self-sensing artificial muscle

Abstract

The invention discloses a length self-sensing artificial muscle, and relates to an inductance type length sensor technology and an artificial muscle technology. A fluid-driven artificial muscle is seamlessly integrated with an inductance type length sensor, the artificial muscle is a fluid-driven elastic telescopic unit, and the inductance type length sensor is a wire winding which is wound outside the artificial muscle and is formed by connecting a plurality of groups of coils in series. The mutual inductance between the wire windings is reduced or increased along with the stretching of the artificial muscle, so that the inductance of the coil is monotonically reduced along with the increase of the length of the artificial muscle. The length of the artificial muscle can be detected in real time by measuring the inductance of the coil, and the resolution is up to the submillimeter level and is not influenced by factors such as load size and deformation speed. The length self-sensing artificial muscle provided by the scheme can be widely applied to various robot systems driven by the artificial muscle, such as an earthworm crawling imitating robot capable of body sensing, a rigid-flexible hybrid bionic arm capable of realizing accurate position control and interactive response, a complex humanoid robot system and the like.

Description

Technical Field

[0001] The invention belongs to the field of inductive sensor technology and artificial muscles, and in particular relates to a length self-sensing artificial muscle. Background Art

[0002] Fluid-driven artificial muscles have attracted widespread attention in the fields of soft robots, bionic rigid-flexible hybrid robots and underwater robots due to their diverse driving forms, fast response and high load-bearing performance. The perception of the artificial muscle's body morphology is crucial for robot control and human-computer interaction.

[0003] At present, there are two methods for artificial muscle self-sensing: one is to indirectly measure the length of the artificial muscle by measuring the driving pressure of the artificial muscle, and the other is to directly integrate strain sensors such as resistive and optical waveguide sensors on the artificial muscle. However, the relationship between the length of the artificial muscle and the driving pressure is relatively complex and is affected by external loads. Most strain sensors are only sensitive to one deformation, either tension or compression, and are difficult to integrate on artificial muscles. Summary of the invention

[0004] In order to solve at least one technical problem in the above-mentioned prior art, the present invention provides a length self-sensing artificial muscle, an artificial muscle driving system, a humanoid arm, and a robot, which realizes submillimeter-level (below 0.01 mm) length self-sensing of artificial muscles. Length sensing based on mutual inductance can monitor the real length of artificial muscles in real time, is not affected by the driving pressure and external load on the artificial muscles, and can achieve long-term stable operation. The length self-sensing artificial muscle has good application prospects in the next generation of soft robots, bionic rigid-flexible hybrid robots, underwater robots and other artificial muscle-driven intelligent robot systems and human-computer interaction interfaces.

[0005] The present invention is achieved through the following technical solutions: According to a first aspect of the present invention, there is provided a length self-sensing artificial muscle, which is formed by seamlessly integrating an inductive length sensor with a fluid-driven artificial muscle, wherein the artificial muscle is an elastic expansion unit driven by the fluid, and the inductive length sensor is a wire winding composed of a plurality of coils connected in series and wound around the artificial muscle. After the inductive length sensor is integrated into the artificial muscle, the distance between each coil of the inductive length sensor changes with the elongation or shortening of the artificial muscle, and the change in the length of the artificial muscle will cause the interaction between each coil of the inductive length sensor to change.

[0006] According to the second aspect of the present invention, in an application case, an artificial muscle driving system is provided, including: the above-mentioned length self-sensing artificial muscle; an air source or a hydraulic source, used to drive the artificial muscle so that the artificial muscle extends or shortens according to the driving pressure received, and the driving pressure includes positive pressure and negative pressure; an inductance measurement circuit, connected to the inductive length sensor, and used to measure the inductance of the inductive length sensor; a controller, used to receive the inductance signal transmitted by the inductance measurement circuit as a feedback signal, thereby adjusting the pressure of the driving air source or the hydraulic source to achieve the artificial muscle length reaching a predetermined value.

[0007] According to a third aspect of the present invention, there is provided a humanoid arm, which comprises: an acrylic thin plate simulating an upper arm, an acrylic thin plate simulating a forearm, and the above-mentioned artificial muscle drive system simulating the biceps brachii, wherein the acrylic thin plate simulating the upper arm and the acrylic thin plate simulating the forearm are connected by a hinge structure, and the two ends of the artificial muscle are respectively fixed on the pressure thin plate simulating the upper arm and the acrylic thin plate simulating the forearm.

[0008] According to a fourth aspect of the present invention, there is provided a robot comprising the above-mentioned humanoid arm, or the above-mentioned artificial muscle drive system, and the robot is a soft robot, or a bionic rigid-flexible hybrid robot.

[0009] Beneficial effects: According to the technical solution of the present invention, a highly sensitive length perception based on mutual inductance is achieved by integrating an inductive length sensor on the outside of the muscle. When the artificial muscle is stretched, the mutual inductance coefficient between the multiple coils of the sensor decreases, and the total inductance of the coils decreases, and vice versa. The length sensing based on mutual inductance achieves sub-millimeter length self-perception, can monitor the real length of the artificial muscle in real time, is not affected by the driving pressure and external load on the artificial muscle, and can achieve long-term stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A stereoscopic diagram of a length self-sensing artificial muscle according to an embodiment of the present invention; Figure 2 A simple structural diagram and working principle of a length self-sensing artificial muscle driving and measuring system according to an embodiment of the present invention; Figure 3 The relationship between the normalized inductance value of the inductive length sensor and the normalized length of the artificial muscle according to the embodiment of the present invention; Figure 4 is the relationship between the length of the artificial muscle and the driving air pressure under different loads according to an embodiment of the present invention; Figure 5 The relationship between the inductance value of the inductive length sensor and the length of the artificial muscle under different loads according to an embodiment of the present invention; FIG6 (a) shows an artificial muscle according to an embodiment of the present invention under a 200 g external load, when the artificial muscle is driven by sinusoidal signals of different frequencies, and the length measured by the inductive length sensor is compared with the length measured by the laser displacement sensor; FIG6 (b) shows an artificial muscle according to an embodiment of the present invention under a 200g external load, when the artificial muscle is driven by square wave signals of different frequencies, and the length measured by the inductive length sensor is compared with the measurement result of the laser displacement sensor; FIG6 (c) is a comparative analysis of the measurement results of the length self-sensing artificial muscle and the laser displacement sensor under different load conditions according to an embodiment of the present invention; Figure 7 The length self-sensing artificial muscle according to an embodiment of the present invention is controlled to perform a length step test under an external load of 100g; Figure 8 The present invention is a working demonstration of an earthworm-like robot based on length self-sensing artificial muscles according to an embodiment of the present invention, wherein (a) is an analysis of the motion principle of the earthworm-like robot according to an embodiment of the present invention; (b) is the perception of the length of the earthworm-like robot body during motion by the length self-sensing artificial muscles according to an embodiment of the present invention at different driving frequencies; Fig. 9 Demonstration of tennis manipulation by a humanoid arm and muscle length perception according to an embodiment of the present invention; Fig.10 Demonstration of accurate positioning of the humanoid arm and muscle length perception according to an embodiment of the present invention; Fig.11 This is a demonstration of humanoid arm interaction and muscle length perception according to an embodiment of the present invention.

[0011] The following are the descriptions of the reference numerals: 1: Artificial muscle; 2: Inductive length sensor; 3: Inductance measurement circuit; 4: Air source; 5: Controller; 6: Twisted pair cable; 7: Air tube. DETAILED DESCRIPTION

[0012] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0013] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0014] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0015] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0016] According to the inventive concept of one aspect of the present invention, in order to solve the problem that the length self-perception of artificial muscles is affected by external loads and is only sensitive to deformation in one direction, the present invention realizes high-sensitivity length perception based on mutual inductance by an inductive length sensor integrated on the outside of the muscle. When the artificial muscle is stretched, the mutual inductance coefficient between the multiple groups of coils of the sensor decreases, and the total inductance of the coils decreases, and vice versa. The inductance of the inductive length sensor is determined only by its own geometric morphology, and has nothing to do with the driving pressure on the artificial muscle, and has nothing to do with the changes in the external load on the artificial muscle. Length sensing based on mutual inductance realizes submillimeter-level length self-perception, can monitor the true length of the artificial muscle in real time, is not affected by the driving pressure and external load on the artificial muscle, and can achieve long-term stable operation. The length self-perception artificial muscle has good application prospects in the next generation of soft robots, bionic rigid-flexible hybrid robots, underwater robots and other artificial muscle-driven intelligent robot systems and human-computer interaction interfaces.

[0017] According to an embodiment of the present invention, a length self-sensing artificial muscle is provided. Figure 1 The following is a stereogram of the length self-sensing artificial muscle according to an embodiment of the present invention. Figure 1The length self-sensing artificial muscle according to an embodiment of the present invention is described. Figure 1 As shown, the length self-sensing artificial muscle is composed of a fluid-driven artificial muscle 1 seamlessly integrated with an inductive length sensor 2, wherein the artificial muscle 1 is a fluid-driven elastic expansion unit such as an elastic bellows, and the inductive length sensor 2 is a wire winding composed of multiple groups of coils connected in series and wound around the artificial muscle.

[0018] After the inductive length sensor 2 is integrated into the artificial muscle 1 , the distance between each coil of the inductive length sensor 2 changes with the extension and contraction of the artificial muscle 1 . The change in the length of the artificial muscle 1 will cause the interaction between each coil of the inductive length sensor 2 to change.

[0019] As the inductive length sensor 2 deforms with the artificial muscle 1, the mutual inductance between the coils in the inductive length sensor 2 changes accordingly, and the inductance value inside the inductive length sensor 2 is the combined effect of the self-inductance of each coil and the mutual inductance between the coils. The inductance value of the inductive length sensor 2 is determined only by its own geometric shape, and has nothing to do with the driving pressure on the artificial muscle 1, and has nothing to do with the change of the external load on the artificial muscle 1.

[0020] In one embodiment, the axial cross-section of the artificial muscle 1 is rectangular, circular or other shapes. The outer wall of the artificial muscle 1 is provided with a platform for integrating the inductive length sensor 2 along the axial direction. The artificial muscle 1 and the inductive length sensor 2 are bonded together by an adhesive, or the inductive length sensor 2 is embedded in the artificial muscle 1, for example, the inductive length sensor 2 is directly bonded to the artificial muscle 1, or bonded to the platform provided on the outer wall of the artificial muscle 1, or the inductive length sensor 2 is directly embedded in the embedding gap provided in the artificial muscle, or embedded in the above-mentioned platform.

[0021] In one embodiment, the number of turns of any coil in the inductive length sensor 2 may be one turn or multiple turns.

[0022] In one embodiment, the fluid drive includes air pressure drive, hydraulic drive or other forms of fluid drive. The coil of the inductive length sensor 2 is a solid conductor coil, a liquid metal coil or other wire winding.

[0023] In one embodiment, the inductive length sensor 2 is composed of a wire wound around a wave crest of a corrugated tube, and the coil of the inductive length sensor is a solid conductor coil or a liquid metal coil.

[0024] According to an embodiment of the present invention, an artificial muscle driving system is also provided. Figure 2 This is a schematic diagram of the simple structure and working principle of the length self-sensing artificial muscle driving and measuring system according to an embodiment of the present invention. Figure 2 As shown, the artificial muscle system includes: a length self-sensing artificial muscle, which is formed by seamlessly integrating an artificial muscle 1 driven by a fluid and an inductive length sensor 2, wherein the artificial muscle 1 is a gas-driven elastic bellows, and the inductive length sensor 2 is a wire winding composed of multiple groups of coils connected in series and wound outside the artificial muscle; an air source 4, which is used to drive the artificial muscle 1, so that the artificial muscle is extended or shortened according to the driving pressure, and the driving pressure includes positive pressure and negative pressure; an inductance measurement circuit 3, which is connected to the inductive length sensor 2 and is used to measure the inductance of the inductive length sensor 2; a controller 5, which is used to receive the inductance signal transmitted by the inductance measurement circuit 3, and drive the air source 4 to output positive pressure or negative pressure to extend or shorten the artificial muscle. In the case of the artificial muscle extending or shortening, the inductive length sensor 2 integrated on the artificial muscle undergoes corresponding deformation, the mutual inductance between each coil is correspondingly reduced or increased, and the inductance of the inductive length sensor changes accordingly. When the length of the artificial muscle 1 is greater than the first target length, the inductance measurement circuit 3 measures an inductance less than the first target inductance, and the controller 5 drives the gas source 4 to output negative pressure to shorten the artificial muscle. Vice versa: when the length of the artificial muscle 1 is less than the second target length, the inductance measurement circuit 3 measures an inductance greater than the second target inductance, and the controller 5 drives the gas source 4 to output positive pressure to extend the artificial muscle. The first target length may be 83.177 mm, the second target length may be 48.884 mm, the first target inductance may be 35.9372 μH, and the second target inductance may be 50.2153 μH. Figure 2 The reference numeral 6 in the figure denotes a twisted pair, and 7 denotes an air pipe.

[0025] As mentioned above, the length self-sensing artificial muscle is made of a fluid-driven artificial muscle seamlessly integrated with an inductive length sensor. Multiple sets of coils wrapped around the artificial muscle are connected in series to achieve high-sensitivity body length sensing based on mutual inductance. In order to simplify the analysis, a pair of single-turn rectangular coils is selected to illustrate the basic principle of the inductive length sensor. According to the Biot-Savart law, the magnetic field generated by a wire with a current of I at any point m (x, y, z) in space is: (1) Where r is the distance between point m and the wire, is the angle between the vector connecting the two ends of the wire and point m and the current vector, is the magnetic permeability of vacuum, and I is the current through the wire.

[0026] A single-turn rectangular coil can be considered as four straight wires connected at the end. Therefore, the magnetic field along the z-axis generated by the rectangular coil with current I at point m is the sum of the components of the magnetic induction intensity along the z-axis generated by the four straight wires at point m. The mutual inductance of the two rectangular coils can be expressed as: (2) Among them, a and b are the length and width of the rectangular coil respectively, and h is the distance between the two rectangular coils. is the magnetic induction intensity along the z-axis direction of the magnetic field generated by one of the two rectangular coils (A) at any point in space with a distance h. x and y are the horizontal and vertical coordinates of the position of the point on the other coil (B) of the two rectangular coils with a distance h.

[0027] The mutual inductance between the two rectangular coils is only related to h. The inductance value of the inductive length sensor can be expressed as: (3) in, is the self-inductance between the coils in the inductive length sensor, is the mutual inductance between the ith coil and the jth coil.

[0028] like Figure 3 As shown (where L0: the inductance of the inductive length sensor when it is not driven by an external force; : The length of the length self-sensing artificial muscle without external drive), the inductance L of the inductive length sensor and the length of the artificial muscle The relationship is monotonic. The fitting curve of formula (4) is obtained from the calibration data: (4) Among them, a and c are coefficients obtained by curve fitting, and e is a natural constant.

[0029] Inductance value of inductive length sensor 2 and artificial muscle The length of the artificial muscle is a monotonic function, which can be used to determine the length, so that artificial muscles can be completed by measuring inductance Measurement of length.

[0030] By integrating the inductive length sensor in the artificial muscle to respond to the deformation of the muscle by lengthening or shortening, the following advantages can be obtained: According to the embodiment of the present invention, Figure 4 As shown, the lengthening or shortening of artificial muscles can be controlled by changing the driving air pressure of the artificial muscles. However, under different loads (load refers to the object to which the artificial muscle applies force), the relationship between the driving air pressure and the length of the artificial muscle is not consistent. Under the same driving air pressure, the lengths of artificial muscles corresponding to different loads are not the same. In addition, due to the viscoelasticity of flexible materials, the lengths of artificial muscles at different times are not the same under the same load and driving air pressure. It is very difficult to achieve self-perception of the length of the artificial muscle itself by detecting the driving air pressure. Figure 5The inductive length sensor integrated in the artificial muscle shown in the figure responds to the deformation as the muscle lengthens or shortens. The inductance value of the sensor is determined only by its own shape and has nothing to do with the driving pressure and external load on the artificial muscle, thus simplifying the self-perception of the artificial muscle length.

[0031] FIG6 (a) is a graph comparing the length measured by the inductive length sensor and the laser displacement sensor when the artificial muscle is driven by sinusoidal signals of different frequencies under an external load of 200g according to an embodiment of the present invention. FIG6 (b) is a graph comparing the length measured by the inductive length sensor and the laser displacement sensor when the artificial muscle is driven by square wave signals of different frequencies under an external load of 200g according to an embodiment of the present invention. FIG6 (c) is a graph comparing the length self-sensing artificial muscle and the laser displacement sensor under different load conditions according to an embodiment of the present invention. According to an embodiment of the present invention, as shown in FIG6 (a), FIG6 (b) and FIG6 (c), in the process of the artificial muscle being driven by different driving signals, the length change curve measured by the inductive length displacement sensor and the length change curve measured by the laser displacement sensor are basically overlapped. Under different load conditions, the length change curves measured by the length self-sensing artificial muscle and the laser displacement sensor are basically overlapped. The length self-sensing artificial muscle has high perception accuracy and good perception effect under different load conditions.

[0032] According to an embodiment of the present invention, Figure 7 As shown in Figure 1, the step guidance data is used as input to the control system to control the artificial muscle movement under an external load of 100g. The monitored real-time length matches the target length very well, except for small overshoots at these points when the muscle length reaches the target length due to the sudden change in the movement state. The stable tracking error is less than 0.2mm under an external load of 100g.

[0033] According to an embodiment of the present invention, there is also provided a humanoid arm, which comprises: an acrylic thin plate simulating an upper arm, an acrylic thin plate simulating a forearm, and the above-mentioned artificial muscle drive system simulating the biceps brachii, wherein the acrylic thin plate simulating the upper arm and the acrylic thin plate simulating the forearm are connected by a hinge structure, and the two ends of the artificial muscle are respectively fixed at appropriate positions of the pressure thin plate simulating the upper arm and the acrylic thin plate simulating the forearm.

[0034] According to an embodiment of the present invention, a robot is further provided, the robot comprising the above-mentioned humanoid arm, or the above-mentioned artificial muscle drive system. In one embodiment, the robot may be a soft robot, or a bionic rigid-flexible hybrid robot.

[0035] About soft robots, Figure 8It is an earthworm-like robot composed of a circular length self-sensing artificial muscle with an integrated inductive length sensor composed of eight sets of coils connected in series. Figure 8 As shown in (a) in the figure, the earthworm-like robot performs telescopic movement by controlling the change of driving pressure. Due to the difference in the friction between its head and tail and the ground, the robot moves forward as a whole during the telescopic movement. As shown in (b) in Figure 8, at different driving frequencies, the length self-sensing artificial muscle can accurately sense the change of the body length.

[0036] Regarding bionic rigid-flexible hybrid robots, length self-sensing artificial muscles can be applied to the field of bionic rigid-flexible hybrid robots and their human-computer interaction interfaces. Figure 9-11 This is a humanoid arm designed based on length self-sensing artificial muscles. The humanoid arm consists of two acrylic sheets simulating the upper arm and the lower arm and a circular length self-sensing artificial muscle simulating the biceps. The upper arm and the lower arm are connected by a hinge structure, and the two ends of the artificial muscle are fixed at appropriate positions on the upper arm and the lower arm respectively. The output signal of the length sensor can be used to control the artificial muscle to perform corresponding extension and contraction movements, thereby driving the lower arm to perform flexion and extension movements. Fig. 9 As shown, the anthropomorphic arm can imitate humans to catch a tennis ball and actively hold the tennis ball to move the arm. After the 3D printed palm installed at the end of the anthropomorphic arm catches the thrown tennis ball, the artificial muscle detects the elongation of the muscle through the load of the tennis ball and the short-term vibration introduced by the impact force and actively changes its own length to drive the anthropomorphic arm to move the tennis ball up and down. After the tennis ball is removed, the artificial muscle contracts instantly. After detecting the length change, the artificial muscle actively stretches to return the anthropomorphic arm to its original position. Fig.10 As shown in the figure, the humanoid arm can achieve precise control of the end position. Four reference points are set along the height direction. By controlling the extension and contraction of the artificial muscles, the movable arm drives the pointer installed at the end to reach the target position. The arm points from the original position to the P1-P4 point, the P4-P1 point, the P4 point, and finally returns to the original position. Fig.11 As shown in the figure, the humanoid arm can interact with the outside world. Use the palm model to touch the humanoid arm from the top and bottom. When the humanoid arm is pushed down, the artificial muscle detects the change in its own length to identify the stimulus and load direction, and actively stretches to drive the arm downward to avoid the stimulus, and vice versa.

[0037] Parts of the present invention that are not disclosed in detail belong to the common knowledge in the art.

[0038] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A length self-sensing artificial muscle, characterized in that: The fluid-driven artificial muscle is seamlessly integrated with an inductive length sensor, wherein the artificial muscle is an elastic expansion unit driven by the fluid, and the inductive length sensor is a wire winding composed of multiple groups of coils connected in series and wrapped around the artificial muscle. After the inductive length sensor is integrated into the artificial muscle, the distance between each coil of the inductive length sensor changes with the extension or shortening of the artificial muscle, and the coil inductance changes accordingly.

2. The length self-sensing artificial muscle according to claim 1, characterized in that: As the artificial muscle lengthens or shortens, the mutual inductance between the coils in the inductive length sensor changes accordingly, and the total inductance value decreases as the length of the artificial muscle increases, and vice versa.

3. The length self-sensing artificial muscle according to claim 1, characterized in that: The inductive length sensor is composed of a wire wound around the crest of a corrugated tube. The coil of the inductive length sensor is a solid conductor coil or a liquid metal coil.

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