Hollow multi-legged stick-slip actuator and driving method

Abstract

The application provides a hollow multi-legged stick-slip actuator and a driving method. The hollow multi-legged stick-slip actuator comprises a bearing plate, a plurality of piezoelectric legs, a driving foot and a control plate. The piezoelectric legs are installed below the bearing plate and comprise a connecting body with a hollow and piezoelectric ceramic pieces arranged on the surface of the connecting body. The driving foot is arranged below the piezoelectric legs. The control plate is used for applying driving voltages with different phases to the piezoelectric legs, changing the bending state and / or upright state of the piezoelectric ceramic pieces and making the driving foot realize multi-degree-of-freedom movement. The piezoelectric ceramic pieces are directly pasted on the connecting body to form the hollow piezoelectric legs for realizing the driving function. The piezoelectric legs are simply pasted on the bearing plate to form the actuator, which greatly reduces the complexity of the actuator manufacturing, reduces the manufacturing and assembly errors and is simple and easy to realize light weight and miniaturization.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric actuator technology, and particularly relates to a hollow multi-legged stick-slip actuator and its driving control method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] A piezoelectric actuator is an actuating element that generates displacement by applying voltage using the inverse piezoelectric effect. Compared with electromagnetic actuators or traditional motors, piezoelectric actuators have many advantages, including simple structure, fast response, high reliability, low power consumption, small size, and no electromagnetic interference. Generally, piezoelectric actuators can be driven by several principles, such as ultrasonic excitation, crawling, and stick-slip. The ultrasonic excitation principle uses ultrasonic vibration (frequency greater than 20kHz) to frictionally drive a slider or rotor, providing good mechanical output, but with low resolution. Piezoelectric actuators operating on the crawling principle mimic the movement of inchworms in nature, converting the minute displacement of the piezoelectric material into a long-stroke output displacement through a stretch-extension-stretching creeping motion. This provides high motion resolution, but the structure is cumbersome and the control strategy is complex. In contrast, piezoelectric actuators employing the stick-slip drive principle rely on the alternating dynamic and static friction forces under sawtooth voltage excitation. During the slow voltage increase phase, the actuator experiences static friction and moves forward; during the rapid voltage decrease phase, the actuator experiences dynamic friction and produces a small amount of retraction. Through this alternation of dynamic and static friction, the actuator accumulates displacement and moves to one side, exhibiting high motion resolution and ease of manufacturing and assembly. Furthermore, through structural design and modal degeneracy, the actuator can achieve various flexible movements. Therefore, in high-precision, high-integration, and high-power-density intelligent industrial scenarios such as optical focusing equipment, robotics, aerospace, and medical applications, stick-slip piezoelectric actuators possess more significant technological advantages and broader application prospects.

[0004] To meet the needs of different applications, various piezoelectric actuators have been developed. Chinese literature CN109302097 B proposes a double-layer piezoelectric actuator that amplifies displacement through the elastic deformation of a metal structure. Its main body includes a first-stage elastic deformation plate, two second-stage elastic deformation plates, two external connecting end caps, and a piezoelectric ceramic. The first-stage elastic deformation plate has a central gap, with a rectangular piezoelectric ceramic fixedly connected to the two inner end faces of the gap. The second-stage elastic deformation plates are symmetrically and parallelly arranged on both sides of the first-stage elastic deformation plate. By designing the elastic deformation of the inner and outer layers of elastic deformation plates, the displacement output by the piezoelectric ceramic is amplified twice. This actuator has advantages such as compact structure and high displacement amplification. Chinese patent document CN 112910304 A proposes a small multi-segment piezoelectric robot and its stick-slip drive excitation method. The robot body comprises three identical sets of "V"-shaped piezoelectric segments and a base. The three sets of "V"-shaped piezoelectric segments are connected in parallel on the base. Each "V"-shaped piezoelectric segment includes a pair of driving legs. When a voltage excitation signal is applied to the driving legs, the legs bend in opposite directions, achieving an opening and closing motion. The combined force of the friction generated by the relative motion of the legs and the working surface serves as the driving force, driving the "V"-shaped piezoelectric segments to achieve stepping motion. By designing voltage excitation signals for the three sets of "V"-shaped piezoelectric segments and controlling their motion sequence, the stick-slip principle is used to excite the robot to achieve planar motion. This small multi-segment piezoelectric robot has advantages such as small size, light weight, simple structure, and high displacement resolution. In addition, the standing wave type hybrid excitation motor and the bidirectional self-propelled traveling wave type linear ultrasonic wave proposed in Chinese patent documents CN 109361326 B and CN 114977879 A can also achieve actuation purposes such as moving the piezoelectric / ultrasonic actuator body or carrying a load.

[0005] Currently, most piezoelectric actuators based on the stick-slip drive principle use hinges or deformation mechanisms to amplify displacement. The complexity of actuator manufacturing and manufacturing / assembly errors severely affect actuator performance. Furthermore, piezoelectric actuators using resonant drive methods suffer from high energy consumption due to their structural characteristics and weak electromechanical coupling. Replacing high-power power supplies with onboard circuitry cannot provide sufficient energy, thus posing a disadvantage in achieving untethered characteristics. Moreover, their large step displacement makes them unsuitable for precision operations. In addition, traditional piezoelectric actuators using stick-slip drive methods are mostly single-degree-of-freedom with insufficient motion accuracy, limiting their application scenarios. For actuators requiring external power, the motion is limited by cable length, restricting the travel distance. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a hollow multi-legged stick-slip actuator and a driving control method. The hollow piezoelectric legs that realize the driving function are formed by directly attaching piezoelectric ceramic sheets to the connector. The piezoelectric legs are simply attached to the carrier plate to form the actuator, which greatly reduces the complexity of actuator manufacturing, reduces manufacturing and assembly errors, and the simple hollow structure is conducive to achieving lightweight and miniaturization.

[0007] To achieve the above objectives, a first aspect of the present invention provides a hollow multi-legged stick-slip actuator, comprising:

[0008] Support plate;

[0009] Multiple piezoelectric legs are mounted below the support plate. Each piezoelectric leg includes a hollow connecting body and a piezoelectric ceramic sheet disposed on the surface of the connecting body.

[0010] A driving foot is disposed below the piezoelectric leg;

[0011] The control board is used to change the bending state and / or upright state of the piezoelectric ceramic sheet, and to apply driving voltages of different phases to the multiple piezoelectric legs, so that the driving legs can achieve multi-degree-of-freedom movement.

[0012] A second aspect of the present invention provides a driving and control method for a hollow multi-legged stick-slip actuator, applied to the aforementioned hollow multi-legged stick-slip actuator, comprising:

[0013] The dimensions of the piezoelectric ceramic sheet are determined such that the resonant frequencies of the second and third bending modes of the piezoelectric ceramic are two and three times the resonant frequency of the first bending mode of the piezoelectric ceramic, respectively.

[0014] A sawtooth wave voltage is applied to the piezoelectric ceramic sheet to drive the vibration of the piezoelectric leg, causing the piezoelectric leg to exhibit a superposition of the first bending mode, the second bending mode, and the third bending mode, thereby realizing the stick-slip drive of the actuator.

[0015] The above one or more technical solutions have the following beneficial effects:

[0016] In this invention, it is proposed to use multiple piezoelectric ceramic sheets directly attached to the connector to form a hollow piezoelectric leg that realizes the driving function. The multiple piezoelectric legs are simply attached to the carrier plate to form an actuator, which greatly reduces the complexity of actuator manufacturing, reduces manufacturing / assembly errors, and the simple hollow structure is conducive to achieving lightweight and miniaturization. The lightweight structure reduces the energy consumption of the actuator and is conducive to onboard circuit integration.

[0017] In this invention, an actuation method for self-motion independent of the slide rail is proposed. A single piezoelectric leg can achieve two degrees of freedom motion in the horizontal plane by bending the piezoelectric ceramic sheet on the opposite side. After multiple piezoelectric legs are combined, rotational motion in the horizontal plane can be achieved by using a differential method. The actuator can complete three degrees of freedom motion of translation and rotation in two directions in the horizontal plane, thus expanding the applicable scenarios.

[0018] This invention proposes a method for powering and driving piezoelectric legs through an electric control board, which eliminates the constraints of power supplies and power cables, making it easier to achieve electromechanical system integration and lightweight performance indicators; the actuator's working stroke is only limited by the battery capacity, enhancing controllability and greatly expanding application scenarios.

[0019] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the hollow multi-legged stick-slip actuator structure in Embodiment 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of the vibration modes of a single piezoelectric leg in Embodiment 2 of the present invention;

[0023] Figure 3 This describes the onboard circuit workflow in Embodiment 1 of the present invention.

[0024] In the diagram, 1 is the piezoelectric ceramic sheet, 2 is the piezoelectric leg, 3 is the support plate, 4 is the drive foot, and 5 is the control board. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0027] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0028] Example 1

[0029] This embodiment discloses a hollow multi-legged stick-slip actuator, comprising:

[0030] Support plate 3;

[0031] Multiple piezoelectric legs 2 are mounted below the support plate 3. Each piezoelectric leg 2 includes a hollow connecting body and a piezoelectric ceramic sheet 1 disposed on the surface of the connecting body.

[0032] Drive foot 4, which is disposed below the piezoelectric leg 2;

[0033] The control board 5 is used to apply driving voltages of different phases to the multiple piezoelectric legs 2, change the bending state and / or upright state of the piezoelectric ceramic sheet 1, and enable the driving foot 4 to achieve multi-degree-of-freedom movement.

[0034] In this embodiment, multiple piezoelectric legs are arranged perpendicularly to the support plate, which makes it easy to achieve large-amplitude, adjustable displacement output.

[0035] This embodiment uses the example of setting four piezoelectric legs as an example, based on a 60×80×80mm... 3 The prototype actuator utilizes structural modulation of the resonant frequencies of the first, second, and third bending modes of the piezoelectric legs to ensure its movement follows the stick-slip principle. Specifically, the actuator mimics the gait of the Siberian roe deer, with all four piezoelectric legs simultaneously engaging in static (stick) or dynamic (slip) friction, enabling three-degree-of-freedom motion and nanometer-level step displacement. Furthermore, the actuator is powered and driven by onboard circuitry, eliminating cable limitations and achieving decimeter-level continuous motion (limited only by battery capacity). At 90V and 2065Hz, under cableless operation, the actuator achieves a minimum step displacement of 12.2nm and a maximum working stroke of 69.2cm, outperforming most traditional stick-slip actuators.

[0036] like Figure 1 As shown in this embodiment, the untethered piezoelectric actuator based on the biomimetic configuration of the Siberian roe deer includes: a piezoelectric ceramic sheet 1, piezoelectric legs 2, a support plate 3, a drive foot 4, and a control plate 5. Four cuboid piezoelectric ceramic sheets 1 are attached to two upper and lower square connectors to form the piezoelectric legs 2. The square connectors have holes punched in the middle to reduce weight.

[0037] Specifically, the actuator consists of four piezoelectric legs 2, and the projections of two piezoelectric legs on the longitudinal section passing through the axis of the piezoelectric leg should coincide as much as possible. At the same time, the polarization directions of the two legs should be consistent. The space is fully utilized to increase the number of piezoelectric ceramic sheets to improve the bending mode quality.

[0038] Each piezoelectric leg 2 is connected to a drive foot 4 at its lower end. The bottom of the drive foot 4 is hemispherical, and the actuator moves by friction with the ground.

[0039] The thickness of the support plate 3 is minimized while ensuring sufficient rigidity, and the four piezoelectric legs 2 are connected together to achieve overall coordinated movement. At the same time, the support plate 3 can be used to support onboard circuits, such as the bottom surface of the actuator's control board 5 can be fixed on the support plate 3 to achieve control of the actuator's movement.

[0040] When a sawtooth wave voltage of the same phase is applied to the piezoelectric ceramic sheet 1 in the same direction, the piezoelectric ceramic sheet 1 bends during the slow voltage rise phase, while the actuator's driving leg 4 remains stationary and moves forward at the top. During the rapid voltage drop phase, the piezoelectric ceramic sheet 1 returns to an upright position, and the driving leg 4 generates kinetic friction, achieving displacement. The phase difference of the applied voltage to the four legs is zero, mimicking the gait of a Siberian roe deer that jumps and lands simultaneously on all four legs. Furthermore, the actuator's speed and direction can be adjusted by adjusting the amplitude and phase of the excitation voltage.

[0041] like Figure 3 As shown, in this implementation, the wireless receiving module receives instructions sent by the computer, controlling the STM32 main controller, the Boost circuit to boost voltage, and the operational amplifier to achieve four-channel output. The instruction execution sequence is as follows: The wireless receiving module integrated into the control board receives the computer instructions and transmits them to the STM32 main controller. The STM32 main controller generates a sawtooth wave with an output frequency and amplitude of 2065Hz and 50V. The 3.7V battery voltage is boosted to 50V using the Boost circuit. The sawtooth wave is amplified by the operational amplifier to increase the output power. Here, the operational amplifier input is a 50V DC signal, and the output signal amplitude is linearly related to the input sawtooth wave amplitude. To improve the impedance matching between the drive circuit and the piezoelectric ceramic sheet, a 10μH inductor is connected in series between the circuit output and the piezoelectric ceramic sheet. Simultaneously, this circuit uses a Boost circuit directly coupled to the STM32, followed by four operational amplifiers and a 10μH series inductor to achieve four-channel voltage output with a 90° phase difference.

[0042] To address the issues of high manufacturing complexity and large manufacturing / assembly errors in traditional piezoelectric actuators that utilize hinges or multi-piece shapes to increase deformation, this paper proposes a method using four piezoelectric ceramic sheets directly bonded to a connector to form hollow piezoelectric legs that achieve the driving function. These four piezoelectric legs are then simply bonded to a connecting / support plate to form the actuator, significantly reducing manufacturing complexity and errors. Furthermore, the simplified hollow structure facilitates lightweighting and miniaturization. Additionally, the lightweight structure reduces the actuator's energy consumption and facilitates onboard circuit integration.

[0043] To address the limitations of motion freedom and application scenarios of piezoelectric actuators that rely on guide rails for motion assistance, a self-motion actuation method is proposed. A single piezoelectric leg can achieve two degrees of freedom motion in the horizontal plane by bending the piezoelectric ceramic sheet on its opposite side. When four piezoelectric legs are combined, rotational motion in the horizontal plane can be achieved by using a differential method. The actuator can then perform three degrees of freedom motion in the horizontal plane, including translation and rotation in two directions, thus expanding its application scenarios.

[0044] To address the challenges of achieving lightweight and miniaturized designs with externally powered piezoelectric actuators, and the limitations imposed by cable length on actuator movement, a method using batteries and onboard circuitry (see workflow) is proposed. Figure 3 The method of powering and driving piezoelectric legs eliminates the constraints of power supplies and cables, making it easier to achieve electromechanical system integration and lightweight performance indicators; the actuator's working stroke is only limited by battery capacity, enhancing controllability and greatly expanding application scenarios.

[0045] Example 2

[0046] The purpose of this embodiment is to provide a driving and control method for a hollow multi-legged stick-slip actuator, which employs a hollow multi-legged stick-slip actuator as described in Embodiment 1, including:

[0047] The dimensions of the piezoelectric ceramic sheet are determined such that the resonant frequencies of the second and third bending modes of the piezoelectric ceramic are two and three times the resonant frequency of the first bending mode of the piezoelectric ceramic, respectively.

[0048] A sawtooth wave voltage is applied to the piezoelectric ceramic sheet to drive the vibration of the piezoelectric leg, causing the piezoelectric leg to exhibit a superposition of the first bending mode, the second bending mode, and the third bending mode, thereby realizing the stick-slip drive of the actuator.

[0049] In this embodiment, the vibration mode of a single piezoelectric leg of the stick-slip actuator is as follows: Figure 2 As shown, the left end is the fixed end of the piezoelectric leg, and the right end is the free end. The shape of the sawtooth wave signal is mainly composed of the fundamental frequency and the signals at the second and third harmonics after its Fourier decomposition. The size design scheme of the piezoelectric ceramic sheet 1 is as follows:

[0050] (1) Thickness of piezoelectric ceramic: The thickness of piezoelectric ceramic 1 is determined to be 0.5mm; here 0.5mm is the thickness of ceramic mass-produced by piezoelectric ceramic manufacturers. Using other thicknesses of ceramic will result in a longer supply cycle and make it difficult to guarantee quality.

[0051] (2) Length and width of piezoelectric ceramic. To ensure that the end of piezoelectric ceramic 1 produces a sawtooth displacement in the time domain, the ratio of the resonant frequencies of the first, second, and third bending modes of piezoelectric ceramic 1 needs to be 1:2:3. Here, the finite element method is used to adjust the length / width of piezoelectric ceramic 1 to calculate the resonant frequencies of each order, so as to satisfy the above relationship. When a sawtooth wave voltage is input, the piezoelectric leg 2 is excited to vibrate and achieve the superposition of the first, second, and third bending modes, thereby reconstructing the sawtooth waveform at the driving foot 4, realizing the efficient driving of the stick-slip mechanism actuator. Inspired by the movement pattern of the Siberian roe deer, the actuator consists of four piezoelectric legs, and all four piezoelectric legs 2 adopt this three-bending mode superposition driving control method. In addition, there is no phase difference between the four piezoelectric legs 2. The actuator thus achieved has high motion accuracy, large load weight, and excellent overall performance.

[0052] Specifically, a single piezoelectric leg is modeled in finite element analysis software. Then, material properties and element types are assigned to each component of the model. The model is then meshed, loads are applied, and simulation type is selected. Finally, the software calculates the resonant frequencies of the three modes.

[0053] Modal analysis was performed using finite element analysis tools to obtain the resonant frequencies of the first, second, and third bending modes. Subsequently, an optimization function was established to examine the correspondence between the size of the piezoelectric ceramic sheet 1 and the resonant frequencies of the three bending modes. The piezoelectric ceramic sheet size corresponding to the extreme points of the optimization function was then determined. Finally, considering the processing / fabrication difficulty, the size of the piezoelectric ceramic sheet 1 was determined.

[0054] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0055] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A hollow multi-legged stick-slip actuator, characterized in that, include: Support plate; Multiple piezoelectric legs are mounted below the support plate. Each piezoelectric leg includes a hollow connecting body and a piezoelectric ceramic sheet disposed on the surface of the connecting body. A driving foot is disposed below the piezoelectric leg; A control board is used to apply driving voltages of different phases to the multiple piezoelectric legs, change the bending state and / or upright state of the piezoelectric ceramic sheet, and enable the driving legs to move with multiple degrees of freedom. The piezoelectric legs are all driven by a superposition of three bending modes: the first bending mode, the second bending mode, and the third bending mode of the piezoelectric ceramic sheet. The resonant frequencies of the second bending mode and the third bending mode of the piezoelectric ceramic sheet are two and three times the resonant frequency of the first bending mode, respectively.

2. The hollow multi-legged stick-slip actuator as described in claim 1, characterized in that, When the control board applies a sawtooth wave voltage of the same phase to the piezoelectric ceramic sheet disposed on the piezoelectric leg in the same direction, during the voltage rise phase, the piezoelectric ceramic sheet bends and the driving leg remains stationary; during the voltage drop phase, the piezoelectric ceramic sheet returns to an upright position and the driving leg generates dynamic friction to achieve displacement.

3. A hollow multi-legged stick-slip actuator as described in claim 1, characterized in that, The voltage phase difference applied by the control board to the plurality of piezoelectric legs is zero.

4. A hollow multi-legged stick-slip actuator as described in claim 1, characterized in that, The lower end of the driving foot is hemispherical.

5. A hollow multi-legged stick-slip actuator as described in claim 1, characterized in that, The speed and direction of the actuator can be adjusted by adjusting the amplitude and phase of the voltage applied to the piezoelectric ceramic sheet by the control board.

6. A hollow multi-legged stick-slip actuator as described in claim 1, characterized in that, The polarization directions of the piezoelectric legs on the same axis are consistent.

7. A hollow multi-legged stick-slip actuator as described in claim 3, characterized in that, The control board includes a main control unit, a boost circuit for voltage boosting, and an operational amplifier. The main control unit generates a sawtooth wave and transmits it to the boost circuit for voltage boosting. The boost circuit receives the sawtooth wave from the main control unit and transmits it to the operational amplifier. The sawtooth wave is then output as a multiplexed drive signal by the operational amplifier.

8. A driving and control method for a hollow multi-legged stick-slip actuator, employing a hollow multi-legged stick-slip actuator as described in any one of claims 1-7, characterized in that, include: The dimensions of the piezoelectric ceramic sheet are determined such that the resonant frequencies of the second and third bending modes of the piezoelectric ceramic sheet are two and three times the resonant frequency of the first bending mode of the piezoelectric ceramic sheet, respectively. A sawtooth wave voltage is applied to the piezoelectric ceramic sheet to drive the vibration of the piezoelectric leg, causing the piezoelectric leg to exhibit a superposition of the first bending mode, the second bending mode, and the third bending mode, thereby realizing the stick-slip drive of the actuator.

9. The driving and control method for a hollow multi-legged stick-slip actuator as described in claim 8, characterized in that, The dimensions of the piezoelectric ceramic sheet are determined as follows: the piezoelectric leg is modeled and modal analysis is performed using finite element analysis software to obtain the resonant frequencies of the first, second, and third bending modes. The resonant frequencies of each mode are calculated by adjusting the length and width of the piezoelectric ceramic sheet, so that the resonant frequencies of the second and third bending modes of the piezoelectric ceramic sheet are respectively twice and three times the resonant frequency of the first bending mode of the piezoelectric ceramic sheet.

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