Miniature Actuators Research Articles

An active metamaterial cell concept for nonreciprocal vibroacoustic transmission

The challenge of inducing stable and robust nonreciprocal transmission of sound is seen as an important milestone on the path towards developing active acoustic metamaterials. Structures that can transmit sound or vibration in a nonreciprocal manner may be considered analogous to an electrical diode and could be useful in many applications, such as noise control and the development of invisible acoustic sensors and acoustic cloaking. This paper focuses on conceptual development and experimental validation of an active metamaterial cell that does not obey the reciprocity principle. The structural cell considered, when activated, significantly attenuates vibration transmission through it in one direction and increases it in the opposite direction. The effect is present in a broad frequency band. The loss of reciprocity is induced by using two concurrent velocity feedback loops with non-collocated sensor-actuator pairs. Inertial accelerometers with time-integrated outputs are used in conjunction with miniature electrodynamic force actuators. The study is first carried out theoretically, using an electromechanically fully coupled lumped parameter model of an otherwise flexible active structure. The derived model is used to conduct analysis of the control system stability and performance. Given that a non-collocated transducer arrangement is considered, special attention is paid to the selection of parameters of the passive system which ensure satisfactory gain margins when the system is made active. In fact, criteria for unconditional stability are derived analytically, in terms of two simple inequalities for the system with idealised sensor-actuator pairs. For realistic transducers, however, unconditional stability is not possible. Nevertheless, if the two inequalities are respected, useful gain margins of the active system can be expected. This is validated experimentally using a dedicated 3D-printed measurement test rig. A substantial reduction of vibration transmission in the desired direction, accompanied by an increase in the opposite one, is recorded experimentally. These results suggest that the control scheme proposed could be used to design an active acoustic metamaterial, which would enable the significantly different transmission of sound depending on the direction it enters such a system.

小型アクチュエータを用いた精密3軸位置決めステージ

小型アクチュエータを用いた精密3軸位置決めステージ

Wireless Miniature Magnetic Phase-Change Soft Actuators.

Wireless miniature soft actuators are promising for various potential high-impact applications in medical, robotic grippers, and artificial muscles. However, these miniature soft actuators are currently constrained by a small output force and low work capacity. To address such challenges, a miniature magnetic phase-change soft composite actuator is reported. This soft actuator exhibits an expanding deformation and enables up to a 70 N output force and 175.2 J g−1 work capacity under remote magnetic radio frequency heating, which are 106–107 times that of traditional magnetic soft actuators. To demonstrate its capabilities, a wireless soft robotic device is first designed that can withstand 0.24 m s−1 fluid flows in an artery phantom. By integrating it with a thermally-responsive shape-memory polymer and bistable metamaterial sleeve, a wireless reversible bistable stent is designed toward future potential angioplasty applications. Moreover, it can additionally locomote inside and jump out of granular media. At last, the phase-change actuator can realize programmable bending deformations when a specifically designed magnetization profile is encoded, enhancing its shape-programming capability. Such a miniature soft actuator provides an approach to enhance the mechanical output and versatility of magnetic soft robots and devices, extending their medical and other potential applications.

Magnetically actuated gearbox for the wireless control of millimeter-scale robots.

The limited force or torque outputs of miniature magnetic actuators constrain the locomotion performances and functionalities of magnetic millimeter-scale robots. Here, we present a magnetically actuated gearbox with a maximum size of 3 millimeters for driving wireless millirobots. The gearbox is assembled using microgears that have reference diameters down to 270 micrometers and are made of aluminum-filled epoxy resins through casting. With a magnetic disk attached to the input shaft, the gearbox can be driven by a rotating external magnetic field, which is not more than 6.8 millitesla, to produce torque of up to 0.182 millinewton meters at 40 hertz. The corresponding torque and power densities are 12.15 micronewton meters per cubic millimeter and 8.93 microwatt per cubic millimeter, respectively. The transmission efficiency of the gearbox in the air is between 25.1 and 29.2% at actuation frequencies ranging from 1 to 40 hertz, and it lowers when the gearbox is actuated in viscous liquids. This miniature gearbox can be accessed wirelessly and integrated with various functional modules to repeatedly generate large actuation forces, strains, and speeds; store energy in elastic components; and lock up mechanical linkages. These characteristics enable us to achieve a peristaltic robot that can crawl on a flat substrate or inside a tube, a jumping robot with a tunable jumping height, a clamping robot that can sample solid objects by grasping, a needle-puncture robot that can take samples from the inside of the target, and a syringe robot that can collect or release liquids.

An underwater piezoelectric energy harvester based on magnetic coupling adaptable to low-speed water flow

The rapid development of the fifth-generation mobile networks (5G) and the Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. To solve the problem of self-powered underwater wireless sensor nodes (WSNs), this paper proposes a magnetically coupled piezoelectric energy harvester (MPEH) based on fluid-induced vibration (FIV) to achieve high-efficiency performance in low-velocity water environments. The results show that compared with the non-magnetic PEH, the initial vibration velocity, velocity bandwidth, and maximum output voltage of the magnetic attraction coupling piezoelectric energy harvester (MAPEH) are increased by 18.42%, 41.38%, and 5.79% respectively. Besides, it is also shown that the vertical distance between the magnets, the diameter, and the mass of the vibrating column have a significant effect on the vibration characteristics, water velocity bandwidth, and performance of the magnetic repulsion coupled piezoelectric energy harvester (MRPEH). The initial vibration velocity of the MRPEH is reduced by 42.1%, and when the water speed is 0.2 m/s, its output voltage is 12.21 times that of the classical configuration. This proposed structure can provide a reference for the optimization of underwater FIV-based PEH, and also lay a foundation for further interconnection of underwater self-powered sensors.

Research on the Inherent Nonlinearity Calibration of the Potentiometer of a Miniature Linear Series Elastic Actuator

This paper presents a miniature Linear Series Elastic Actuator (LSEA), in which two low-cost linear potentiometers were adopted to achieve a compact design. To improve the measurement accuracy of the linear potentiometer, a novel Bezier-based Calibration Method (BCM) and its optimization method were proposed to calibrate the inherent nonlinearity of the linear potentiometer. Calibration efficiency of the BCM was investigated numerically by making a comparison with the widely used Polynomial Calibration method (PCM), and the effect of the BCM calibration on the control performance of the LSEA was investigated experimentally by displacement and force control. Results reveal that the BCM exhibits an excellent local calibration ability for the nonlinearity with knee points. Due to the above characteristic, the BCM could produce a better calibration accuracy than the PCM under the same model order and improve the control performance of the LSEA. In addition, the BCM could calibrate the inherent nonlinearity of the potentiometer in a continuous form rather than that of piecewise ones. The continuous calibration form could bring more convenience to practical applications.

Concentric Dual-Chamber Pneumatic Artificial Muscles: Miniature Actuators Designed for Use in Minimally Invasive Surgical Instruments

Development of high-performance flexible surgical instruments is important to simplify and enable new minimally invasive surgical procedures. New actuation technologies are necessary to produce flexible instrumentation that is capable of accessing difficult-to-reach anatomy and performing laborious tasks without damaging delicate tissues. Recently, concentric McKibben muscles and dual-chamber pneumatic artificial muscles (PAMs) have been proposed for use in miniature flexible robotic surgical instrumentation. In this study, several varieties of a hybrid concentric dual-chamber PAM design are built and their force generation and stroke length are compared to a contractile McKibben muscle. The concentric dual-chamber PAM is designed to provide surgical access for large diameter (1.5–2.0 mm) instruments to be delivered to the surgical site in a pneumatically sealed actuator suitable for miniaturization and integration into surgical devices used in fluid environments (fetal applications in particular). Force output of the concentric dual-chamber PAM is modeled and compared to experimental results. Initial results suggest that the newly introduced design produces a higher actuation force per unit length than traditional McKibben muscles. The prototype dual-channel PAM produced a maximum 15.25 N of force and 8.39 mm of stroke, in comparison to 13.31 N of force and 19.3 mm of stroke produced by a traditional contractile McKibben muscle of the same length, outer diameter, and materials.

Design and characterization of a 3D printed miniature actuator using shape memory alloy wires

Microfluidics has been at the center of attention in chemical and biological sciences over the last decade since it can miniaturize many laboratory-based applications. However, the transition from concept to a practical microfluidic chip is greatly hindered due to the widespread conventional soft lithography techniques which are used for the fabrication of the microfluidic chips. These methods are not time- and cost-efficient. Additive manufacturing technique (i.e. 3D printing) has grown in many research fields. Many conventional microfluidic system component designs have been adapted to the 3D printing manufacturing techniques. Three-dimensional printed active components such as microvalves and micropumps have also been studied, however, almost all the designs depend on an external pneumatic control unit or syringe pumps so far. In this study, we aimed to address the lack of a microfluidic active component with an integrated actuator unit. We used a shape memory alloy as the actuator. In doing so, we employed an innovative batch fabrication method that utilizes 3D printing. The proposed actuator design can produce high work and concurrently isolate the heat source from the fluidic sample which is of utmost importance for biological samples. The results show that the miniature actuator can block high pressure (up to 150 mmHg) silicone channel partially or completely depending on the application requirements. The actuation time can be controlled electronically and reduced to times as low as 100 ms. In conclusion, this design proved to be a promising candidate for the development of flow control components such as microvalves, micropumps, or micromixers.

Electroactive Polymer-Based Soft Actuator with Integrated Functions of Multi-Degree-of-Freedom Motion and Perception.

Soft actuators have received extensive attention in the fields of soft robotics, biomedicine, and intelligence systems owing to their advantages of pliancy, silence, and essential safety. However, most existing soft actuators have only single actuation elements and lack sensing. Therefore, it is difficult for them to perform complex motions with multiple degrees of freedom (multi-DOFs) and high precision. This article reports a miniature columnar dielectric elastomer actuator (DEA) with multi-DOF actuation and sensing, which was fabricated with an electroactive polymer acrylic film (Very High Bond [VHB] acrylic film by 3M Company) and carbon black grease electrodes. The arrangement of the simulation electrodes on the VHB was optimized to realize multi-DOF actuation, and the sensing electrodes were configured on the outer part of the DEA to realize real-time sensing. The results showed that the soft actuator can achieve all-round actuation through the selective power of the stimulation electrodes with a controllable voltage. The maximum bending angle and axial strain of the actuator reached 50° and 13%, respectively. Moreover, the deformation modes, direction, and quantity could be precisely measured using the integrative sensing function. In addition, to demonstrate the advantages of the proposed actuator, a manipulator with multiple actuators was designed and controlled to realize different actions of screwing and grasping with sensing. This research is useful not only for the design of multifunctional soft actuators but also for the development of soft robots with flexible, complex, and precisely controllable motions.

Rapid Actuation of Thermo-Responsive Polymer Networks: Investigation of the Transition Kinetics.

The swelling and collapsing of thermo-responsive poly(N-isopropylacrylamide)-based polymer (pNIPAAm) networks are investigated in order to reveal the dependency on their kinetics and maximum possible actuation speed. The pNIPAAm-based network was attached as thin hydrogel film to lithographically prepared gold nanoparticle arrays to exploit their localized surface plasmon resonance (LSPR) for rapid local heating. The same substrate also served for LSPR-based monitoring of the reversible collapsing and swelling of the pNIPAAm network through its pronounced refractive index changes. The obtained data reveal signatures of multiple phases during the volume transition, which are driven by the diffusion of water molecules into and out of the network structure and by polymer chain re-arrangement. For the micrometer-thick hydrogel film in the swollen state, the layer can respond as fast as several milliseconds depending on the strength of the heating optical pulse and on the tuning of the ambient temperature with respect to the lower critical solution temperature of the polymer. Distinct differences in the time constants of swelling and collapse are observed and attributed to the dependence of the cooperative diffusion coefficient of polymer chains on polymer volume fraction. The reported results may provide guidelines for novel miniature actuator designs and micromachines that take advantages of the non-reciprocal temperature-induced volume transitions in thermo-responsive hydrogel materials.

Origami Inspired Design for Capsule Endoscope to Retrograde Using Intestinal Peristalsis

Capsule endoscopy has gained a lot of attention in the medical field in the recent past as an effective way of investigating unusual symptoms experienced in places such as esophagus, stomach, small intestine and colon. However, motion control of the capsule endoscope is challenging and often requires a power source and miniature actuators. To address these issues, we present a novel origami inspired structure as an attachment to the capsule endoscope. The proposed origami structure utilizes the wave generated by peristalsis of the intestine to move it forward and backward. When the origami structure is folded, the capsule endoscope is propelled forward by intestinal peristalsis. When the origami structure is unfolded, the intestinal peristalsis squeezes the origami structure to drive the capsule endoscope to move in the opposite direction. Therefore, folding and unfolding of the proposed origami structure would allow to control the movement direction of the capsule endoscope. In this letter, we present the design, simulations and experimental validation of the proposed origami structure.

Magnetic Miniature Actuators with Six‐Degrees‐of‐Freedom Multimodal Soft‐Bodied Locomotion

Magnetic Miniature Actuators Magnetic miniature robots have great potential to transform robotics, materials science and biomedicine. In article number 2100259, Zhan Lum and co-workers present a magnetic miniature robot that has seven modes of soft-bodied locomotion with six-degrees-of-freedom. To exhibit its unprecedented dexterity, this untethered robot is commanded to negotiate across obstacles, which are impassable by existing small-scale devices.

Miniature coiled artificial muscle for wireless soft medical devices.

Wireless small-scale soft-bodied devices are capable of precise operation inside confined internal spaces, enabling various minimally invasive medical applications. However, such potential is constrained by the small output force and low work capacity of the current miniature soft actuators. To address this challenge, we report a small-scale soft actuator that harnesses the synergetic interactions between the coiled artificial muscle and radio frequency–magnetic heating. This wirelessly controlled actuator exhibits a large output force (~3.1 N) and high work capacity (3.5 J/g). Combining this actuator with different mechanical designs, its tensile and torsional behaviors can be engineered into different functional devices, such as a suture device, a pair of scissors, a driller, and a clamper. In addition, by assuming a spatially varying magnetization profile, a multilinked coiled muscle can have both magnetic field–induced bending and high contractile force. Such an approach could be used in various future untethered miniature medical devices.

Design of a Low-Cost Air Bearing Testbed for Nano CMG Maneuvers

In this paper, a low-cost, miniature spacecraft attitude control simulator is presented for testing miniature actuators such as Nano Control Moment Gyroscopes (CMGs) for simple maneuvers. The experimental setup is composed by an attitude control system (ACS) that mainly consists of a four-CMG cluster in a pyramid configuration and a custom-made air bearing. The one-degree-of-freedom (DoF) air bearing is fabricated to reproduce the frictionless conditions of a nano-satellite in orbit. The ACS is made exclusively using low-cost commercial-off-the-shelf (COTS) components, whilst the air bearing is made using 3D-printed parts. Both hardware and software implementations are described in detail and the performance of the developed simulator is evaluated by two maneuver experiments. Despite the manufacturing imperfections, the ACS is capable of providing higher angular velocities than previously presented in the literature while following the theoretical or simulation data. The results indicate that it is possible to manufacture a low-cost, miniature actuator such as a CMG, using COTS components to demonstrate the operation of an agile nano-satellite. Any deviations from the theoretical values are addressed and several improvements are discussed to further enhance the performance of the air bearing testing platform.

Magnetic Miniature Actuators with Six‐Degrees‐of‐Freedom Multimodal Soft‐Bodied Locomotion

Magnetic miniature robots (MMRs) are mobile actuators that can exploit their size to noninvasively access highly confined, enclosed spaces. By leveraging on such unique abilities, MMRs have great prospects to transform robotics, biomedicine, and materials science. As having high dexterity is critical for MMRs to enable their targeted applications, existing MMRs have developed numerous soft‐bodied gaits to locomote in various environments. However, there exist two critical limitations that have severely restricted their dexterity: 1) MMRs capable of multimodal soft‐bodied locomotion have only demonstrated five‐degrees‐of‐freedom (five‐DOF) motions because the sixth‐DOF rotation about their net magnetic moment axis is uncontrollable; 2) six‐DOF MMRs have only realized one mode of soft‐bodied, swimming locomotion. Herein, a six‐DOF MMR is proposed that can execute seven modes of soft‐bodied locomotion and perform 3D pick‐and‐place operations. By optimizing its harmonic magnetization profile, the MMR can produce 1.41–63.9‐fold larger sixth‐DOF torque than existing MMRs with similar profiles, without compromising their traditional five‐DOF actuation capabilities. The proposed MMR demonstrates unprecedented dexterity: it can jump through narrow slots to reach higher grounds; use precise orientation control to roll, two‐anchor crawl, and swim across tight openings with strict shape constraints; and perform undulating crawling across three different planes in convoluted channels. An interactive preprint version of the article can be found at: https://www.authorea.com/doi/full/10.22541/au.164087652.25227465.

Lift Generation by a Miniature Piezoelectric Ultrasonic Motor-Driven Rotary-Wing for Pico Air Vehicles

Actuators are key components for further miniaturization of insect-scale microrobots. It is challenging to create a new miniature actuator suited for rotary-wing pico aerial vehicles (PAVs), which have a wing span of a few centimeters and a mass of a few grams. In this paper, we propose a miniature piezoelectric ultrasonic motor that permits high-speed rotation at a sufficient torque to achieve the flight of the simplest device comprising the proposed motor and rotor blades. The prototype motor, which employs a bending vibration mode as a principle, measures 1.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.6$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times2$ </tex-math></inline-formula> mm and weighs 25 mg. The experimental results show that the miniature motor rotates rotor blades having a length of 20 mm with an angular velocity of over 1800 rad/s. The thrust force generated from this system exceeds its total mass of 110 mg and successfully lifts the system. Although the flight is tethered, the set of the proposed motor and rotor blades demonstrates a takeoff that represents the possibility of rotary-wing PAVs.

Piezoelectric-Thermal Coupling Driven Biomimetic Stick-Slip Bidirectional Rotary Actuator for Nanomanipulation.

Substantial improvement of rotation driving accuracy is urgently needed and facing challenges. Miniature bidirectional rotary actuators with high-precision and controllable fallback rate require novel driving principles. Here, on the basis of a proposed biomimetic stick-slip motion principle, a novel piezoelectric-thermal coupling bidirectional rotary actuator was developed. The integrated mantis grasping leglike biomimetic claws and heating rods could realize the clockwise macroscopic rotation and anticlockwise macroscopic fallback of a cylindrical rotator, generated by piezoelectric stick-slip and thermal expansion, respectively. The rotation fallback was effectively inhibited at relatively lower frequencies and higher voltages, as a slight fallback rate of 0.095 was confirmed in term of 0.5 Hz and 80 V. An extraordinary piezoelectric-driven macroscopic rotation resolution of 0.2 μrad and thermal-induced microscopic resolution of 0.00073°/°C were experimentally revealed with the aid of real-time observation of the clockwise slow sticking and anticlockwise instantaneous slipping processes by using three-dimensional optical imaging.

Improving the comprehensive performance of miniature MR rotary actuators using a lamellar excitation structure

Miniaturization has increasingly become a crucial prerequisite in various magnetorheological (MR) drive application scenarios. Owing to their high controllability and low response time, MR rotary actuators are developed for numerous feasible actuation solutions. However, the incident low degradation efficiency in the miniaturization limits the application of MR rotary actuators. In addition to torque capacity, structural simplification and easy machinability are also essential for miniaturization. In this study, a novel lamellar excitation structure (LES), which is interleaved with induction coils and ring-shaped iron cores, is proposed to improve the comprehensive performance of a miniature MR rotary actuator. The optimisation of the magnetic field distribution is realised by adopting an equivalent magnetic modelling method. The miniature MR actuator is incorporated into a turbine generator to evaluate the torque capability of the proposed LES-incorporated MR actuator via a kinematic model of the rotating shaft. The LES-incorporated MR rotary actuator demonstrates more favourable deceleration efficiency and torque capacity than conventional MR rotary actuators. The speed reduction per unit power Δn/P can be increased by 500% at most. The torque enhancement ratio-to-volume ratio value of LES is approximately 80 times higher than that of other optimised structures. We believe that this study is significant in improving the comprehensive performance of miniature MR rotary actuators, expanding the applications of MR actuators in miniaturised scenarios.

Piezoelectric MEMS—evolution from sensing technology to diversified applications in the 5G/Internet of Things (IoT) era

The rapid development of the fifth-generation mobile networks (5G) and Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. Piezoelectric microelectromechanical system (MEMS) devices, fabricated by micromachining technologies, provide a versatile platform for various high-performance sensors, actuators, energy harvesters, filters and oscillators (main building blocks in radio frequency front-ends for wireless communication). In this paper, we provide a comprehensive review of the working mechanism, structural design, and diversified applications of piezoelectric MEMS devices. Firstly, various piezoelectric MEMS sensors are introduced, including contact and non-contact types, aiming for the applications in physical, chemical and biological sensing. This is followed by a presentation of the advances in piezoelectric MEMS actuators for different application scenarios. Meanwhile, piezoelectric MEMS energy harvesters, with the ability to power other MEMS devices, are orderly enumerated. Furthermore, as a representative of piezoelectric resonators, Lamb wave resonators are exhibited with manifold performance improvements. Finally, the development trends of wearable and implantable piezoelectric MEMS devices are discussed.

Multistage Digital-to-Analogue Chip Based on a Weighted Flow Resistance Network for Soft Actuators.

A control chip with a multistage flow-rate regulation function based on the correlation between the flow resistance and flow rate has been developed in this article. Compared with the traditional proportional solenoid valve, this kind of flow valve based on microfluidic technology has the characteristics of being light-weight and having no electric drive. It solves such technical problems as how the current digital microfluidic chip can only adjust the flow switch, and the adjustment of the flow rate is difficult. To linearize the output signal, we propose a design method of weighted resistance. The output flow is controlled by a 4-bit binary pressure signal. According to the binary value of the 4-bit pressure signal at the input, the output can achieve 16-stage flow adjustment. Furthermore, we integrate the three-dimensional flow resistance network, multilayer structure microvalve, and parallel fluid network into a single chip by using 3D printing to obtain a modular flow control unit. This structure enables the microflow control signal to be converted from a digital signal to an analogue signal (DA conversion), and is suitable for microflow driving components, such as in microfluidic chip sampling systems and proportional mixing systems. In the future, we expect this device to even be used in the automatic control system of a miniature pneumatic soft actuator.