A triboelectric variable-stiffness soft gripper state monitoring sensor and its testing method

Abstract

The present invention proposes a triboelectric variable stiffness soft gripper state monitoring sensor and a testing method thereof. The sensor comprises an angle monitoring unit and a stiffness monitoring unit. The angle monitoring unit comprises a silicone substrate and a liquid metal electrode. Signal output ports are provided at the ends of both sides of the liquid metal electrode to monitor resistance changes. The stiffness monitoring unit comprises an aluminum ball electrode and an external wrapping device. The external wrapping devices are connected by a silicone adhesive, and the aluminum ball is filled inside the wrapping device. The aluminum ball can not only serve as a detection element in the overall structure of the soft finger, but also as a stiffness adjustment element of the finger. When the gripper bends, the liquid metal layer stretches to change the resistance. When the gripper changes stiffness, the external wrapping device contacts the aluminum ball to change the voltage of the aluminum ball electrode, and different electrical signals are generated as the stiffness changes. The present invention can realize the detection of the bending angle and stiffness of the soft gripper, and has the advantages of a wide measurement range, high measurement accuracy and long service life.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a triboelectric variable-rigidity soft gripper state monitoring sensor and a testing method thereof. Background Art

[0002] With the development of the logistics industry, traditional logistics in warehousing and sorting can no longer meet the fast-paced needs of the current society due to its low timeliness and high cost, which has become the main reason hindering the development of the logistics industry. In recent years, intelligent logistics has flourished. Through intelligent technologies such as cyber-physical systems and the Internet of Things, intelligent analysis is achieved to improve the efficiency of logistics operations. In order to improve the efficiency and flexibility of unmanned sorting, rigid manipulators are widely used in sorting systems and have achieved remarkable results. However, rigid manipulators are mostly made of metal materials, with poor safety and limited adaptability. Especially in the sorting process of fragile and brittle objects such as fruits and eggs, it is easy to cause epidermal damage, making it difficult to achieve lossless sorting, resulting in certain economic losses. In recent years, soft grippers have received widespread attention due to their inherent flexibility and strong adaptability. They are expected to achieve lossless sorting and are currently widely used in the manufacturing industry.

[0003] Sensors, as a bridge connecting machines and computers, are crucial in the process of intelligence. On the one hand, soft grippers need sensors to monitor gripping behavior. On the other hand, they need to be able to simulate human hands while ensuring flexibility, change stiffness when grasping different weights, and enhance robustness. The potentiometers and encoders in traditional sensors limit the nonlinear deformation of soft grippers, affecting the flexibility of soft grippers, and are not suitable for use in the field of soft gripper gripping behavior monitoring. Currently, common soft gripper behavior monitoring methods include light detection, conductive nanocomposites, and electromagnetic effects. However, the above methods still have some drawbacks. For example, conventional visual recognition does not work in dark spaces. If a light source is added alone, the mechanism will be too complicated, and electromagnetic effect detection requires the addition of an additional magnetic field.

[0004] Therefore, there is an urgent need to design a new monitoring structure that is simple in structure, easy to integrate, highly precise, stable and reliable, which can not only meet the variable stiffness requirements of the gripper, but also monitor various parameters of the gripper in real time to meet the needs of miniaturization and intelligence of modern mechanical equipment. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of designing a variable stiffness soft gripper state monitoring sensor with simple structure, easy integration, high precision, stability and reliability to meet the current problem of intelligent sorting in the logistics industry, and propose a triboelectric variable stiffness soft gripper state monitoring sensor and its testing method. The sensor and its testing method can realize real-time monitoring of the bending angle and stiffness of the soft gripper.

[0006] The present invention is achieved through the following technical scheme. The present invention proposes a triboelectric variable-stiffness soft gripper state monitoring sensor, the sensor comprising: an angle monitoring unit 2 and a stiffness monitoring unit 3, the angle monitoring unit 2 comprising an upper substrate 21, a liquid metal electrode layer 22 and a lower substrate 23, the stiffness monitoring unit 3 comprising a substrate 31, an aluminum ball electrode 32, an aluminum ball sleeve 33 and a restriction layer 34, wherein the aluminum ball sleeve 33 is provided with an exhaust hole 331, and the upper substrate 21 and the substrate 31 overlap.

[0007] Furthermore, the upper substrate 21 of the angle monitoring unit 2 is connected to the soft gripper 1 through Sil-Poxy silicone adhesive, the lower substrate 23 is cast on the basis of the upper substrate 21, and the liquid metal electrode layer 22 is injected into the channel between the upper substrate 21 and the lower substrate 23 through a syringe.

[0008] Furthermore, the base 31 of the stiffness monitoring unit 3 is connected to the aluminum ball sleeve 33 via Sil-Poxy silicone adhesive, the aluminum ball sleeve 33 is connected to the restriction layer 34 via Sil-Poxy silicone adhesive, and the aluminum ball electrode 32 fills the rectangular chamber composed of the base 31 , the aluminum ball sleeve 33 and the restriction layer 34 .

[0009] Furthermore, the upper substrate 21 and the lower substrate 23 are both made of Dragon skin 30, and the liquid metal is liquid gallium-indium-tin-bismuth alloy.

[0010] Furthermore, the aluminum ball electrode 32 is composed of a solid aluminum ball, the aluminum ball sleeve 33 is made of Dragon skin 30, and the limiting layer 34 is made of epoxy resin.

[0011] Furthermore, the liquid metal electrode layer 22 includes 8 channels, each of which is arranged in parallel, and the overall shape is rectangular. Each channel is 133 mm long and 1 mm wide. The overall length of the liquid metal electrode layer 22 is 136 mm and the overall width is 24.5 mm.

[0012] Furthermore, output ports are provided at the ends of both sides of the liquid metal electrode layer 22 to reserve space for the arrangement of electrical signal output wires, and the length of the output ends on both sides is 5 mm and the width is 4 mm.

[0013] Furthermore, as the soft gripper 1 bends, the upper substrate 21 and the lower substrate 23 are stretched, the middle channel becomes narrower, the liquid metal electrode layer 22 becomes thinner and longer, the resistance changes, and the resistance changes with the degree of bending.

[0014] Furthermore, when the stiffness monitoring unit 3 is evacuated, the contact area between the silica gel in the rectangular chamber and the aluminum ball of the aluminum ball electrode 32 changes with the change of the evacuation pressure, and the voltage of the aluminum ball electrode 32 changes with the change of the contact area with the silica gel.

[0015] The present invention proposes a method for testing the triboelectric variable-stiffness soft gripper state monitoring sensor, which specifically includes the following steps:

[0016] Step S1: using an electrostatic collection device to record the electrical signal generated by the triboelectric variable stiffness soft gripper state monitoring sensor, and converting the original sinusoidal signal into a square wave signal through a signal processing module to improve the signal stability and reduce the complexity of the detection signal;

[0017] Step S2: Using a professional camera to record the bending angle and vacuum pressure of the soft gripper 1;

[0018] Step S3: Based on the output electrical signal and the recorded angle and pressure, the bending angle of the soft gripper 1 is characterized by resistance change, and the stiffness of the soft gripper 1 is characterized by voltage change.

[0019] Beneficial effects of the present invention:

[0020] (1) In the sensor proposed by the present invention, when the gripper bends, the gripper drives the angle monitoring unit to stretch and bend, the length of the liquid metal electrode in the angle monitoring unit increases, the cross-sectional area decreases, and the resistance changes accordingly. The output resistance value will change synchronously with the bending angle of the gripper, so the functional relationship between the gripper bending angle and the resistance can be obtained by collecting and summarizing the resistance values ​​at different bending angles.

[0021] (2) For the sensor proposed by the present invention, when the gripper changes stiffness, the gap between the aluminum balls in the aluminum ball electrode decreases, the contact tightness increases, the contact area with the external silicone increases, and the voltage changes accordingly. The output voltage will change synchronously with the vacuum pressure, so the functional relationship between the gripper stiffness and the voltage can be obtained by collecting the voltage value and the gripper stiffness value under different vacuum pressures. Since the sensor is integrated with the variable stiffness structure, it has an ultra-long service life and extremely high stability, and can realize the angle and speed detection of the soft gripper. It has the advantages of self-driven sensing, wide detection range, high measurement accuracy and long service life.

[0022] (3) The present invention has the characteristics of miniaturization and integration, and can realize real-time monitoring of the bending angle and stiffness of the gripper while maintaining the integrity and functional integrity of the gripper, providing a theoretical and experimental basis for the development of a new type of self-driving and self-sensing soft gripper. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1This is a schematic diagram of the structure of the triboelectric variable stiffness soft gripper state monitoring sensor of the present invention;

[0024] Figure 2 It is a structural schematic diagram of the angle monitoring unit in the triboelectric variable stiffness soft gripper state monitoring sensor of the present invention;

[0025] Figure 3 It is a schematic diagram of the structure of the liquid metal electrode layer in the angle detection unit of the present invention;

[0026] Figure 4 for Figure 3 A magnified schematic diagram of point A;

[0027] Figure 5 It is a structural schematic diagram of the stiffness monitoring unit in the triboelectric variable stiffness soft gripper state monitoring sensor of the present invention;

[0028] Figure 6 This is a flow chart of a testing method for the triboelectric variable stiffness soft gripper state monitoring sensor of the present invention;

[0029] Figure 7 It is a schematic diagram of the voltage characteristics of the triboelectric variable stiffness soft gripper state monitoring sensor at different frequencies according to the present invention;

[0030] Figure 8 The monitoring diagram of the triboelectric variable stiffness soft gripper state monitoring sensor described in the present invention, wherein (a) is a schematic diagram of the fitting curve of the bending angle and the resistance; and (b) is a schematic diagram of the fitting curve of the gripper stiffness and the voltage.

[0031] Fig. 9 This is a result diagram of a durability test of the triboelectric variable stiffness soft gripper state monitoring sensor of the present invention;

[0032] Explanation of the reference numerals: 1-soft gripper; 2-angle monitoring unit; 21-upper substrate; 22-liquid metal electrode layer; 23-lower substrate; 3-rigidity monitoring unit; 31-substrate; 32-aluminum ball electrode; 33-aluminum ball sleeve; 34-restriction layer. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0034] Combination Figure 1-Figure 9The present invention proposes a triboelectric variable-stiffness soft gripper state monitoring sensor, the sensor comprising: an angle monitoring unit 2 and a stiffness monitoring unit 3, the angle monitoring unit 2 comprising an upper substrate 21, a liquid metal electrode layer 22 and a lower substrate 23, the stiffness monitoring unit 3 comprising a substrate 31, an aluminum ball electrode 32, an aluminum ball sleeve 33 and a restriction layer 34, wherein the aluminum ball sleeve 33 is provided with an exhaust hole 331, and the upper substrate 21 and the substrate 31 overlap.

[0035] The upper substrate 21 of the angle monitoring unit 2 is connected to the soft gripper 1 through Sil-Poxy silicone adhesive, the lower substrate 23 is cast on the basis of the upper substrate 21, and the liquid metal electrode layer 22 is formed by injecting a syringe into the channel between the upper substrate 21 and the lower substrate 23. The liquid metal electrode is injected into the channel between the upper and lower substrates as an electrode material. After the injection is completed, the liquid metal should completely fill the inside of the channel, and each prepared liquid metal electrode has the same initial resistance.

[0036] The base 31 of the stiffness monitoring unit 3 is connected to the aluminum ball sleeve 33 through Sil-Poxy silicone adhesive, the aluminum ball sleeve 33 is connected to the restriction layer 34 through Sil-Poxy silicone adhesive, and the aluminum ball electrode 32 fills the rectangular chamber composed of the base 31, the aluminum ball sleeve 33 and the restriction layer 34.

[0037] The upper substrate 21 and the lower substrate 23 are both made of Dragon skin 30, and the liquid metal is liquid gallium-indium-tin-bismuth alloy.

[0038] The aluminum ball electrode 32 is composed of a solid aluminum ball, the aluminum ball cover 33 is made of Dragon skin 30, and the limiting layer 34 is made of epoxy resin.

[0039] The liquid metal electrode layer 22 includes 8 channels, each of which is arranged in parallel, has the same size and spacing, and is rectangular in shape. Each channel is 133 mm long and 1 mm wide. The liquid metal electrode layer 22 has an overall length of 136 mm and an overall width of 24.5 mm.

[0040] Signal output ports are provided at both ends of the liquid metal electrode layer 22 to monitor resistance changes, and space is reserved for the arrangement of electrical signal output wires. The output ends on both sides are 5 mm long and 4 mm wide.

[0041] The working principle of the angle monitoring unit 2 is as follows: as the soft gripper 1 bends, the upper substrate 21 and the lower substrate 23 are stretched, the middle channel becomes narrower, the liquid metal electrode layer 22 becomes thinner and longer, the resistance changes, and the resistance changes with the degree of bending.

[0042] The working principle of the stiffness monitoring unit 3 is as follows: a through hole is provided on one side of the aluminum ball sleeve 33 for connecting a pipeline to evacuate the aluminum ball electrode 32. When the aluminum ball sleeve 33 is evacuated through the evacuation hole 331, the rectangular chamber composed of the substrate 31, the aluminum ball sleeve 33 and the restriction layer 34 is sunken inward under the action of the external air pressure, reducing the gap between the aluminum balls in the aluminum ball electrode 32, improving the stiffness of the stiffness monitoring unit 3, and inhibiting the bending of the soft gripper 1. The stiffness increases with the increase of the evacuation pressure. At the same time, the contact area between the silicone in the rectangular chamber and the aluminum ball of the aluminum ball electrode 32 increases with the increase of the evacuation pressure. At this time, the gap between the aluminum ball electrode 32 and the external silicone is reduced, generating a potential difference, i.e., an open circuit voltage. After the evacuation is completed, due to the difference in electronegativity, electrons flow from the ground to the aluminum ball electrode, and a voltage signal is continuously generated. When the evacuation hole 331 releases the vacuum pressure on the aluminum ball sleeve 33, the force of the external air pressure is released, and the stiffness of the stiffness monitoring unit 3 is reduced. The negative charge on the surface of the aluminum ball electrode 32 drives the free electrons to flow from the aluminum ball electrode 32 to the ground, resulting in the accumulation of positive charge in the external silica gel, generating a voltage signal in the opposite direction.

[0043] The present invention proposes a method for testing the triboelectric variable-stiffness soft gripper state monitoring sensor, which specifically includes the following steps:

[0044] Step S1: using an electrostatic collection device to record the electrical signal generated by the triboelectric variable stiffness soft gripper state monitoring sensor, and converting the original sinusoidal signal into a square wave signal through a signal processing module to improve the signal stability and reduce the complexity of the detection signal;

[0045] Step S2: Using a professional camera to record the bending angle and vacuum pressure of the soft gripper 1;

[0046] Step S3: According to the output electrical signal and the recorded angle and pressure, the bending angle of the soft gripper 1 is characterized by resistance change (the resistance is matched with the bending angle to obtain a function curve), and the stiffness of the soft gripper 1 is characterized by voltage change (the voltage is matched with the gripper stiffness to obtain a function curve).

[0047] like Figure 7 As shown, it is a schematic diagram of the voltage characteristics of the triboelectric variable stiffness soft gripper state monitoring sensor at different frequencies. The experimental results show that the voltage signal amplitude of the sensor described in the present invention will change with the increase of the gripper variable stiffness frequency, but gradually tends to be stable.

[0048] like Figure 8As shown, it is a monitoring schematic diagram of the friction electric variable stiffness soft gripper state monitoring sensor described in the present invention. The experimental results show that the resistance of the sensor described in the present invention has a certain linear relationship with the bending angle of the gripper, and the gripper stiffness also has a certain linear relationship with the voltage. The resistance signal and voltage signal of the sensor described in the present invention can better reflect the bending information of the gripper.

[0049] like Fig. 9 As shown in the figure, the durability test result of the triboelectric variable stiffness soft gripper state monitoring sensor described in the present invention is carried out. The experimental results show that after 1500 times (1.5 hours) of continuous bending and changing stiffness, the output voltage amplitude is still stable at 9V without obvious attenuation, which reflects the ultra-long service life of the sensor described in the present invention.

[0050] Since the variable stiffness structure of the sensor is integrated with the sensing structure, it has an extremely long service life and extremely high stability, and can achieve self-driven sensing, a wide detection range, and high detection accuracy.

[0051] The triboelectric variable-stiffness soft gripper state monitoring sensor proposed in the embodiment of the present invention has the characteristics of miniaturization and integration. It can realize real-time detection of the bending angle and stiffness of the gripper under the premise of the structural integrity and functional integrity of the gripper, and provide a theoretical and experimental basis for the development of new self-driven and self-sensing intelligent bearings.

[0052] The above is a detailed introduction to a friction electric variable stiffness soft gripper state monitoring sensor and a testing method thereof proposed in the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A triboelectric variable stiffness soft gripper state monitoring sensor, characterized in that: The sensor comprises: an angle monitoring unit (2) and a stiffness monitoring unit (3), wherein the angle monitoring unit (2) comprises an upper substrate (21), a liquid metal electrode layer (22) and a lower substrate (23), and the stiffness monitoring unit (3) comprises a substrate (31), an aluminum ball electrode (32), an aluminum ball sleeve (33) and a restriction layer (34), wherein an air extraction hole (331) is provided on the aluminum ball sleeve (33), and the upper substrate (21) and the substrate (31) overlap; The upper substrate (21) of the angle monitoring unit (2) is connected to the soft gripper (1) via Sil-Poxy silicone adhesive, the lower substrate (23) is cast on the upper substrate (21), and the liquid metal electrode layer (22) is injected into the channel between the upper substrate (21) and the lower substrate (23) via a syringe; The base (31) of the stiffness monitoring unit (3) is connected to the aluminum ball sleeve (33) by Sil-Poxy silicone adhesive, the aluminum ball sleeve (33) is connected to the restriction layer (34) by Sil-Poxy silicone adhesive, and the aluminum ball electrode (32) fills the rectangular parallelepiped chamber formed by the base (31), the aluminum ball sleeve (33) and the restriction layer (34); As the soft gripper (1) bends, the upper substrate (21) and the lower substrate (23) are stretched, the middle channel becomes narrower, the liquid metal electrode layer (22) becomes thinner and longer, the resistance changes, and the resistance changes with the degree of bending; When the stiffness monitoring unit (3) is evacuated, the contact area between the silica gel in the rectangular chamber and the aluminum ball of the aluminum ball electrode (32) changes as the evacuation pressure changes, and the voltage of the aluminum ball electrode (32) changes as the contact area with the silica gel changes.

2. The sensor according to claim 1, characterized in that The upper substrate (21) and the lower substrate (23) are both made of Dragon skin 30, and the liquid metal is liquid gallium-indium-tin-bismuth alloy.

3. The sensor according to claim 1, characterized in that The aluminum ball electrode (32) is composed of a solid aluminum ball, the material of the aluminum ball sleeve (33) is Dragon skin 30, and the material of the restriction layer (34) is epoxy resin.

4. The sensor according to claim 1, characterized in that The liquid metal electrode layer (22) comprises 8 channels, each of which is arranged in parallel and has an overall rectangular shape. Each channel has a length of 133 mm and a width of 1 mm. The overall length of the liquid metal electrode layer (22) is 136 mm and the overall width is 24.5 mm.

5. The sensor according to claim 4, characterized in that Output ports are provided at the ends of both sides of the liquid metal electrode layer (22), which reserve space for the arrangement of electrical signal output wires. The output ends on both sides are 5 mm in length and 4 mm in width.

6. A method for testing a sensor according to any one of claims 1 to 5, characterized in that: The method specifically comprises the following steps: Step S1: using an electrostatic collection device to record the electrical signal generated by the triboelectric variable stiffness soft gripper state monitoring sensor, and converting the original sinusoidal signal into a square wave signal through a signal processing module to improve the signal stability and reduce the complexity of the detection signal; Step S2: Using a professional camera to record the bending angle and vacuum pressure of the soft gripper (1); Step S3: Based on the output electrical signal and the recorded angle and pressure, the bending angle of the soft gripper (1) is characterized by resistance change, and the stiffness of the soft gripper (1) is characterized by voltage change.

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