A new self-sensing twisted-wire actuator for flexible robot actuation

Abstract

The present invention discloses a novel self-sensing twisted-wire actuator for flexible robot drive, comprising a drive motor, a pair of self-sensing twisted wires, a pair of V-shaped adaptive adjustment mechanisms, a resistance analyzer, and a load. The present invention utilizes a flexible twisted wire with self-sensing resistance in the actuator. When the twisted wires become entangled, the internal conductive network structure changes, causing a change in the twisted wire resistance. By measuring the twisted wire resistance, the degree of twisted wire contraction is inferred, enabling the twisted-wire actuator's position self-sensing function. Simultaneously, when a load is connected to the twisted-wire actuator, the adaptive adjustment mechanism that controls the twisted-wire spacing deforms, adjusting the spacing accordingly, thereby changing the transmission ratio of the twisted-wire actuator system and enhancing the adaptability of the twisted-wire actuator.

Description

Technical Field

[0001] The present invention relates to the field of flexible sensing and driving technology, and in particular to a novel self-sensing twisted wire driver for flexible driving of robots. Background Art

[0002] Traditional robotic actuators are primarily based on electric motors, requiring rigid and complex reduction gear transmission mechanisms. This results in large, heavy, and complex robots. These robots perform well in highly structured environments, such as industrial production lines. However, when deployed in open environments, such as homes and those requiring extensive human-robot interaction, their inherent bulk and rigidity pose significant application limitations and safety risks. Inspired by the structure and movement patterns of biological muscles, researchers have developed a variety of novel actuator mechanisms that emulate biological motion patterns by exploring specialized materials that deform in response to external stimuli (including temperature, electric fields, and magnetic fields). Compared to traditional electric motor actuators, these novel actuators offer significant advantages in power-to-weight ratio, compliance, and structural simplicity, demonstrating significant potential for application in robotic exoskeletons and biomimetic soft robots. Currently, reported novel actuators include piezoelectric actuators, electroactive polymer (EAP) actuators, shape memory alloy / polymer (SMA / SMP) actuators, soft fluid actuators, supercoiled polymer (SCP) actuators, and twisted wire actuators. New actuators vary in their core materials and operating principles, resulting in varying performance. Twist-wire actuators convert a motor's rotational motion into linear motion by winding single or multiple twisted wires. Their simple structure offers the dual advantages of good compliance and high output force, making them highly practical in applications such as biomimetic soft robotics.

[0003] Traditional torsion-wire actuators mostly use ultra-high molecular weight polyethylene (UHMWPE) high-horsepower cable as the torsion wire. While this cable offers high strength and output force, it is still too rigid compared to human muscle. To achieve closed-loop force or displacement control, traditional torsion-wire actuators often use external force or displacement sensors. These rigid sensors significantly reduce the actuator's flexibility and increase its complexity. Traditional torsion-wire actuators generally cannot automatically adjust their transmission ratio based on load size to adapt to environmental changes, limiting their practicality. Summary of the Invention

[0004] In order to solve the problems of poor flexibility, complex structure, lack of environmental adaptability, and inability to achieve compact closed-loop control of traditional drivers, the present invention designs a new self-sensing twisted wire driver for flexible driving of robots.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] A novel self-sensing twisted wire driver for flexible robot drive has the following structural features: it includes: a drive motor, a pair of self-sensing twisted wires, a pair of V-shaped adaptive adjustment mechanisms, a resistance analyzer, and a load; one opening of the adaptive adjustment mechanism is fixed downward at the end of the drive motor shaft, and the other opening is upward for connecting the load at the bottom, and the openings of the two adaptive adjustment mechanisms are opposite to each other; two self-sensing twisted wires are fixed in parallel and at intervals between the two adaptive adjustment mechanisms; the resistance analyzer is connected in series with one self-sensing twisted wire to detect changes in the twisted wire resistance.

[0007] Furthermore, the self-sensing twisted wire includes a rubber outer shell and a conductive inner core filled in the rubber outer shell. The rubber outer shell enhances the force-bearing capacity. The conductive inner core is made of a conductive composite material, which is simple to manufacture and low in cost. The conductive composite material itself is inherently flexible and will deform under the action of force. When the self-sensing twisted wire is stretched, the conductive network structure formed by the conductive filler in the conductive composite material changes, resulting in a change in the resistance of the self-sensing twisted wire. By measuring the resistance of the self-sensing twisted wire, the degree of contraction of the twisted wire is calculated, thereby realizing the position self-sensing function of the twisted wire driver.

[0008] Furthermore, a self-sensing twisted wire is connected to the resistance analyzer via a silver wire. The external silver wire is soft and thin, making the driver more compact without compromising its flexibility. The resistance analyzer is a DC impedance analyzer, which is easy to purchase and inexpensive.

[0009] Furthermore, the driving motor drives the torsion wire to twist, and the torsion wire resistivity and contraction displacement change with the number of motor turns, so that the self-sensing torsion wire changes with the torsional resistance of the driving motor, wherein there is a certain nonlinear relationship between the torsion wire resistivity-contraction displacement-number of motor turns. Based on this relationship of the torsion wire, the self-sensing function of the torsion wire is realized, and the control of the driver displacement output is realized.

[0010] Furthermore, the adaptive adjustment mechanism of the present invention is a V-shaped elastic rod. When the load is connected to the torsion wire drive, the V-shaped elastic rod that controls the torsion wire spacing automatically deforms and adjusts the torsion wire spacing accordingly, thereby changing the transmission ratio of the torsion wire drive system and enhancing the adaptability of the torsion wire drive.

[0011] The beneficial effects of the present invention are embodied in:

[0012] The self-sensing twisted wire driver of the present invention, while retaining the characteristics of a traditional twisted wire driver, applies a flexible twisted wire with a resistance self-sensing function to the driver, thereby greatly improving the flexibility of the twisted wire driver. When the twisted wire is entangled, the internal conductive network structure changes, resulting in a change in the twisted wire resistance. By measuring the resistance of the twisted wire, the degree of contraction of the twisted wire is calculated, thereby realizing the position self-sensing function of the twisted wire driver. The self-sensing twisted wire driver of the present invention can achieve closed-loop control of force or displacement by simply utilizing the sensing performance of the twisted wire itself without any external force or displacement sensor, greatly improving the flexibility of the twisted wire driver, reducing the size and mass of the driver, and making the structure of the twisted wire driver more compact. At the same time, when a load is connected to the twisted wire driver, the adaptive adjustment mechanism that controls the twisted wire spacing is deformed, and the twisted wire spacing is adjusted accordingly, thereby changing the transmission ratio of the twisted wire driver system and enhancing the adaptability of the twisted wire driver. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the structure of the self-sensing twisting actuator of the present invention;

[0014] Figure 2 A schematic diagram of the motion principle of the self-sensing twisting actuator of the present invention;

[0015] Figure 3 Schematic diagram of the conductive network structure change of the self-sensing twisted wire of the present invention;

[0016] Figure 4 This is a schematic diagram of the structure of the standardized test platform for the self-sensing twisting drive of the present invention;

[0017] Figure 5 Graph showing the relationship between the degree of contraction of the twisted wire (rate of change of twisted wire length) and the number of motor rotations in the self-sensing twisted wire driver of the present invention;

[0018] Figure 6 Graph showing the relationship between the rate of change of twisted wire resistance and the rate of change of twisted wire length in the self-sensing twisted wire driver of the present invention;

[0019] Figure 7 This is a control flow chart of the self-sensing twisting drive of the present invention;

[0020] The numbers in the figure are: 1 is the drive motor; 2 is the self-sensing twist wire; 3 is the adaptive adjustment mechanism; 4 is the resistance analyzer; 5 is the load; 6 is the linear guide; 7 is the angle encoder; 8 is the force sensor; and 9 is the linear encoder. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solution in this embodiment of the present invention in conjunction with the drawings in this embodiment of the present invention. Obviously, the embodiment described is only one embodiment of the present invention, not all embodiments of the present invention. Based on this embodiment of the present invention, all other embodiments of the present invention obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] like Figure 1 As shown, this embodiment provides a new self-sensing torsion wire driver for flexible drive of a robot, comprising: a drive motor 1, a pair of self-sensing torsion wires 2, a pair of V-shaped adaptive adjustment mechanisms 3, a resistance analyzer 4 and a load 5; one opening in the adaptive adjustment mechanism 3 is fixed downward at the end of the motor shaft of the drive motor 1, and the other opening is upward for connecting the load 5 at the bottom, and the openings of the two adaptive adjustment mechanisms are opposite to each other; two self-sensing torsion wires 2 are fixed in parallel and at intervals between the two adaptive adjustment mechanisms 3; the resistance analyzer 4 is connected in series with a self-sensing torsion wire 2 to detect changes in torsion wire resistance in real time.

[0023] The drive motor 1 can be a small rotary DC motor, which acts as a power source to drive the adaptive adjustment mechanism to rotate synchronously. The motor's rotation causes the twisted wires to entangle with each other, causing them to twist and contract in the longitudinal direction, thereby converting the motor's rotational motion into linear movement of the load.

[0024] Adaptive adjustment mechanism 3 is a V-shaped elastic rod. When different loads are connected to the torsion drive, the elastic rod deforms, correspondingly reducing or increasing the torsion wire spacing, thereby changing the system's transmission ratio. This adapts to the varying load capacity and speed requirements of the torsion drive in different environments, enhancing the torsion drive's environmental adaptability.

[0025] like Figure 2 The figure shows a schematic diagram of the motion principle of the self-sensing torsion wire actuator of the present invention, wherein (a), (b), and (c) correspond to the torsion wire actuator when no load is applied, when load is applied, and when load is applied and the actuator rotates a certain angle, respectively. X0, X1, and X are the axial lengths of the torsion wire when no load is applied, when load is applied, and when load is applied and the actuator rotates a certain angle, respectively. d0, d1, and d are the distances between the two ends of the V-bar of the adaptive adjustment mechanism when no load is applied, when load is applied, and when load is applied and the actuator rotates a certain angle, respectively. ΔX is the displacement caused by the contraction of the torsion wire of the torsion wire actuator after the load is applied and the motor rotates a certain angle.

[0026] In a specific implementation, the self-sensing twisted wire 2 includes a rubber shell and a conductive inner core filled in the rubber shell. The conductive inner core is made of a conductive composite material, which is simple to manufacture and low in cost. The conductive composite material itself is inherently flexible and will deform under the action of force. Figure 3 As shown, when the self-sensing twisted wire is stretched, the conductive network structure formed by the conductive filler inside the conductive composite material changes, resulting in a change in the twisted wire resistance. By measuring the twisted wire resistance, the degree of contraction of the twisted wire is inferred, thus realizing the position self-sensing function of the twisted wire actuator. In a specific implementation, a conductive composite material with multi-walled carbon nanotubes as the conductive filler and polydimethylsiloxane (PDMS) as the matrix can be used. The manufacturing process of the self-sensing twisted wire based on this can be as follows:

[0027] Weigh an appropriate amount of multi-walled carbon nanotubes and pour it into a beaker. Then add 60mL of n-hexane and ultrasonically disperse it for 1 hour to obtain a conductive filler suspension. Add 30g of PDMS-A component to the conductive filler suspension and mechanically stir it at 600rpm for 3h. Remove the n-hexane in the process of promoting uniform dispersion of the conductive filler. After the n-hexane in the mixture is completely removed, add 3g of PDMS-B component and mechanically stir it at 600rpm for 10min to ensure uniform mixing. In the above steps, due to the high-speed mechanical stirring, a large number of bubbles are mixed into the mixture, which will seriously affect the overall performance of the composite material and must be removed. The mixture is ultrasonically treated to promote the bubbling of bubbles, and then the mixture is placed in a vacuum box with a vacuum degree of 101KPa for 15min to completely remove the bubbles in the mixture. The mixture after degassing is drawn into a rubber tube through a syringe and sealed at both ends. The mold is directly placed in a blast drying box and cured at 80℃ for 2h to obtain a self-sensing twist line.

[0028] In a specific implementation, the resistance analyzer 4 is a DC impedance analyzer, and a self-sensing twisted wire is connected to the resistance analyzer through a silver wire. The external silver wire is soft and thin, making the driver more compact without destroying its flexibility.

[0029] To verify the performance of the self-sensing twisting drive of this embodiment, the following settings are made: Figure 4 The standardized test platform shown is supported by a high-precision linear guide 6. A small rotating DC motor with a power of less than 200W is selected as the drive motor 1. Motors with excessive power will interfere with the sensor. An adaptive adjustment mechanism 3, a self-sensing torsion wire 2, and a load 5 with appropriate type and parameters are selected. A high-precision resistance analyzer 4, an angle encoder 7, a force sensor 8, and a linear encoder 9 are configured to measure the resistance of the torsion wire, the motor's rotation angle, the load size, and the linear movement distance of the load. The drive motor twists the torsion wire, and the torsion wire resistivity and contraction displacement change with the number of motor turns. There is a certain nonlinear relationship between torsion wire resistivity, contraction displacement, and number of motor turns. This nonlinear relationship was determined through experiments conducted on the standardized test platform. Figure 5 The relationship between the degree of twist contraction (the rate of change of twist length) and the number of motor rotations is shown. Figure 6The relationship between the rate of change of twisted wire resistance and the rate of change of twisted wire length is shown. The figure shows a nonlinear relationship between twisted wire resistance, contraction displacement, and number of motor turns. This relationship allows the magnitude of twisted wire contraction to be estimated based on the change in twisted wire resistance, thereby enabling self-sensing of the twisted wire's position. Since the magnitude of twisted wire contraction is determined by the force acting on it, the force acting on the twisted wire can also be estimated based on the change in twisted wire resistance, enabling force sensing of the twisted wire.

[0030] In specific implementation, Figure 7 The control flow chart for a self-sensing twisted wire actuator is shown below: After the motor rotates a certain angle, the self-sensing twisted wire contracts accordingly. By measuring the change in resistance before and after the twisted wire contracts, the twisted wire contraction value is estimated. This value is compared with a given twisted wire contraction value, and the motor continues rotating based on the difference until the twisted wire contraction value reaches a given theoretical value. This self-sensing twisted wire actuator, without any external force or displacement sensors, achieves closed-loop displacement control solely by utilizing the twisted wire's inherent sensing properties. This significantly improves the actuator's flexibility, reduces its size and mass, and makes the actuator more compact.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A new self-sensing twisted wire actuator for flexible driving of robots, characterized in that: include: A driving motor (1), a pair of self-sensing twisted wires (2), a pair of V-shaped adaptive adjustment mechanisms (3), a resistance analyzer (4) and a load (5); one opening of the adaptive adjustment mechanism (3) is fixed downward at the end of the motor shaft of the driving motor (1), and the other opening is upward for connecting the load (5) at the bottom, and the openings of the two adaptive adjustment mechanisms are opposite to each other; two self-sensing twisted wires (2) are fixed in parallel and at intervals between the two adaptive adjustment mechanisms (3); the resistance analyzer (4) is connected in series with one self-sensing twisted wire (2); The self-sensing twisted wire (2) comprises a rubber outer shell and a conductive inner core filled in the rubber outer shell, wherein the conductive inner core is made of a conductive composite material with multi-walled carbon nanotubes as conductive fillers and polydimethylsiloxane (PDMS) as a matrix; a self-sensing twisted wire (2) is connected to the resistance analyzer (4) via a silver wire; The adaptive adjustment mechanism (3) is a V-shaped elastic rod. When different loads are connected to the twisted wire drive, the elastic rod deforms, correspondingly reducing or increasing the twisted wire spacing, thereby changing the transmission ratio of the system.

2. The novel self-sensing twisting actuator according to claim 1 is characterized in that: The resistance analyzer (4) is a DC impedance analyzer.

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