Miniature Actuators Research Articles

Structuring of electrorheological fluids in polymer matrices for miniature actuators

Miniature actuators are utilized in various application fields, from robotics to medical devices, where compact dimensions, precise movements, and cost-effectiveness are crucial factors. Particularly for applications like braille displays, there is a critical demand for lightweight, portable, and affordable actuators to integrate into daily life for visually impaired people. However, existing actuation technologies such as electroactive polymers, electrorheological materials, and piezoelectric elements often do not meet the specific requirements of miniature actuators, especially for braille displays. Therefore, this study investigates the behavior of electrorheological fluids incorporated into polymer matrices of cellulose and proteins for miniature actuators to overcome the primary challenge of sedimentation through the structuring of the liquid. The gel formulations are tested in three distinct setups: the V-shaped, horizontal plates, and valve system. These experiments demonstrated immediate structural changes in the gel formulations, achieving reversible movement. Furthermore, the valve setup even enabled the analysis of the strength of the hardened mixtures by the resistance against applied air pressure. The results demonstrate that incorporating electrorheological fluids into polymer matrices is not only feasible but also preserves the characteristic behavior of electrorheological fluids under electrical field exposure. This behavior validates the applicability and suitability of modified electrorheological fluid mixtures in miniature actuators.

A Self-Propelled Linear Piezoelectric Micro-Actuator Inspired by the Movement Patterns of Aquatic Beetles.

The locomotion mechanisms and structural characteristics of insects in nature offer new perspectives and solutions for designing miniature actuators. Inspired by the underwater movement of aquatic beetles, this paper presents a bidirectional self-propelled linear piezoelectric micro-actuator (SLPMA), whose maximum size in three dimensions is currently recognized as the smallest known of the self-propelled piezoelectric linear micro-actuators. Through the superposition of two bending vibration modes, the proposed actuator generates an elliptical motion trajectory at its driving feet. The size was determined as 15 mm × 12.8 mm × 5 mm after finite element analysis (FEA) through modal and transient simulations. A mathematical model was established to analyze and validate the feasibility of the proposed design. Finally, a prototype was fabricated, and an experimental platform was constructed to test the driving characteristics of the SLPMA. The experimental results showed that the maximum no-load velocity and maximum carrying load of the prototype in the forward motion were 17.3 mm/s and 14.8 mN, respectively, while those in the backward motion were 20.5 mm/s and 15.9 mN, respectively.

A water strider-inspired intestinal stent actuator for controllable adhesion and unidirectional biofluid picking

Soft-bodied aquatic organisms exhibit extraordinary navigation and mobility in liquid environments which inspiring the development of biomimetic actuators with complex movements. Stimulus-responsive soft materials including hydrogels and shape-memory polymers are replacing traditional rigid parts that leading to dynamic and responsive soft actuators. In this study, we took inspiration from water strider to develop a biomimetic actuator for targeted stimulation and pH sensing in the gastrointestinal tract. We designed a soft and water-based Janus adhesive hydrogel patch that attaches to specific parts of the intestine and responds to pH changes through external stimulation. The hydrogel patch that forms the belly of the water strider driver incorporates an inverse opal microstructure that enables pH responsive behavior. The hydrogel patch on the water strider's leg uses a sandwich structure of Cu particles to convert light into heat and bend under infrared light to mimic the water strider's leg simulating the efficient and steady movement of the water strider's leg which transporting the biological fluid in one direction. This miniature bionic actuator demonstrates controlled adhesion and unidirectional biofluid delivery capabilities, proving its potential for targeted stimulus response and pH sensing in the gastrointestinal tract, thus opening up new possibilities for medical applications in the growing field of soft actuators.

Coupled magneto-mechanical response of laminate composites comprising a layer of Ni-Mn-Ga microparticles

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs), exhibiting a giant magnetic field induced strain (MFIS), high work output and fast response, are highly promising materials for emerging technologies to be used in automotive, aerospace, and robotics industries, among others. Their magnetic-to-mechanical energy conversion ability is characterized by the coupled magneto-mechanical response they show when magnetic field and mechanical stress are simultaneously applied. In the present work we elaborated a series of laminated composites comprising a layered ensemble of single crystalline Ni-Mn-Ga microparticles built-in between Cu foils via small layers of silicone rubber. Such a simple and robust design enabled an in-depth study of the simultaneous influence of the magnetic field and compressive opposing stress on MFIS and the generated force of the particle layer driving out-of-plane magnetomechanical response of the laminate. Self-consistent parameters characterizing a magnetic field- and stress-induced martensitic variant reorientation in the particles were disclosed by the measurements and comprehensive analysis of both the magnetization curves under opposing constant stresses (complemented by tracking residual strains with X-ray µ-CT imaging) and compressive stress-strain dependences under transversal magnetic field. In particular, an accurate value of the magnetic-to-mechanical energy conversion coefficient, equal to Cme = (2.3 ± 0.13) MPa/T2, and the value of maximum magnetostress of about 2.3 MPa generated by microparticles were determined, in a good agreement with bulk Ni-Mn-Ga single crystals (SC). In contrast to bulk SC, particles are technologically and costly more efficient. They have much higher degree of freedom in terms of composites design allowing the development of advanced miniature actuators and sensors.

Fully 3D-Printed Miniature Soft Hydraulic Actuators with Shape Memory Effect for Morphing and Manipulation.

Miniature shape-morphing soft actuators driven by external stimuli and fluidic pressure hold great promise in morphing matter and small-scale soft robotics. However, it remains challenging to achieve both rich shape morphing and shape locking in a fast and controlled way due to the limitations of actuation reversibility and fabrication. Here, fully 3D-printed, sub-millimeter thin-plate-like miniature soft hydraulic actuators with shape memory effect (SME) for programable fast shape morphing and shape locking, are reported. It combines commercial high-resolution multi-material 3D printing of stiff shape memory polymers (SMPs) and soft elastomers and direct printing of microfluidic channels and 2D/3D channel networks embedded in elastomers in a single print run. Leveraging spatial patterning of hybrid compositions and expansion heterogeneity of microfluidic channel networks for versatile hydraulically actuated shape morphing, including circular, wavy, helical, saddle, and warping shapes with various curvatures, are demonstrated. The morphed shapes can be temporarily locked and recover to their original planar forms repeatedly by activating SME of the SMPs. Utilizing the fast shape morphing and locking in the miniature actuators, their potential applications in non-invasive manipulation of small-scale objects and fragile living organisms, multimodal entanglement grasping, and energy-saving manipulators, are demonstrated.

A Millimeter‐Scale Micro Crawling Robot with Fast‐Moving Driven by a Miniature Electromagnetic Linear Actuator

The micro crawling robot exhibits significant potential applications in various fields such as fault detection, disaster relief, and environmental monitoring. This article introduces a high‐performance millimeter scale crawling robot driven by a miniature electromagnetic linear actuator (MELA) with a body length of 5–6 mm and a mass of 80 mg. In this article, the working principle of the micro robot is analyzed and validated, and the influence of current, frequency, and angle α between the direction of actuator's force and the crawling surface on the crawling speed are analyzed through experiments. Results show that the optimal α ranges from 50° to 55°, and a specific current and frequency are identified to achieve maximum crawling speed for robot with particular α. When α is 50°, with a current of 300 mA and a frequency of 200 Hz, the robot reached the maximum speed of 20.2 Body Length s−1(BL s−1). The proposed robot can crawl at 12 BL s−1 with a load of 110 mg, and support a maximum load of 400 mg. Additionally, the robot demonstrated diverse capabilities such as climbing on a 10° slope with a load of 110 mg, jumping on a 1 mm obstacle, and crawling on surfaces of various materials.

A miniature piezoelectric actuator with fast movement and nanometer resolution

To accomplish fast movement and high positioning capability, a miniature self-moving piezoelectric actuator (MSPA) is developed with two groups of polyphenylene sulfide (PPS) transducers operating in the symmetric bending (SB) or counter symmetric bending (CSB) vibration. Each group includes the inner and outer legs, whose vibrations are orthogonal and horizontal to the ground, respectively; this interestingly imitates the stepping and swing functions of the forelimbs and hindlimbs of the gorilla in the ‘running on all fours’ gait. To examine the validity, first, by utilizing the model on the basis of Krimhertz transmission theory, the resonant frequency of the CSB vibration was structurally tuned to approach that of the SB vibration. Then, a MSPA prototype with the size of 30 × 45 × 49 mm and the weight of 25.2 g was fabricated to assess the moving, carrying, and positioning performance. In a tethered manner, the MSPA yielded the maximal speed of 562 mm/s (18.73 body length per second), the maximal payload of 485 g (19.25 times of its own weight), and the towing force of 0.5 N (corresponding to the towing force density of 19.8 N/kg). Moreover, it achieved the turning movements (whose directions, angular speeds, and steering radii are changeable) and in-situ rotations, climbed the slope of 12.5°, and moved on the curved floor. In an untethered manner, the MSPA produced the minimal step displacement of 31.9 nm. These results demonstrate that the MPSA possesses the large speed and the nanometer resolution owing to the bionic operating principle and the employment of PPS, and provides a new approach to design lightweight piezoelectric actuators.

Development of a New Cable-Driven Planar Parallel Continuum Robot Using Compound Kinematic Calibration Method

Abstract This paper presents the design, calibration, and development of a novel cable-driven planar parallel continuum robot (PCR). The PCR employs a novel drive unit, which is mainly composed of cables, guiding pulleys, and miniature linear actuators. The kinematic model of the PCR is derived based on the constant curvature assumption and the space vector method, and its workspace and singularity are analyzed. In addition, this paper adopts a novel compound kinematic calibration method, which includes the linear calibration method in the robot-specific model and the use of genetic algorithm (GA) in the robot-independent model. To verify the validity of the calibration method, the pose accuracy is assessed by providing positional points on the elliptical trajectory, and the trajectory tracking accuracy is evaluated by using circular and rectangular trajectories. The experimental results show that the static positioning accuracy is maintained at 1 mm; meanwhile, the trajectory tracking accuracy is controlled within the range of 0.9–1.4 mm. The PCR developed in this paper shows good comprehensive performance by employing the proposed novel compound kinematic calibration method.

A miniature multi-DOF ring-shaped piezoelectric actuator capable of driving both flat and spherical movers

In this paper, a novel miniature piezoelectric actuator was proposed with a compact ring structure and four driving teeth. The prominent feature was that the ring-shaped piezoelectric actuator could not only drive multiple types of movers, but also achieve multi-DOF motions by using the hybrid and traveling vibration modes. On the one hand, the four teeth were driven by only one ring-shaped piezoelectric actuator instead of four actuators separately, and were arranged circumferentially capable of supporting and driving both flat and spherical movers. On the other hand, the 4th-order radial and axial vibration modes were degenerated to achieve linear motions in the ox and oy directions; while two 3rd-order axial vibration modes were hybrid to realize the rotary motion around oz direction. FEM (finite element method) was employed to determine parameters and verify the working principles. Then, a prototype with a size of about Φ60 × 13 mm3 and a weight of 40 g was fabricated, and the characteristics were tested. Experimental results showed that the maximum speed, resolution and load realized in the linear motions were 23.3 mm/s, 0.7 μm, and 200 g, respectively; while that in the rotary motions were 0.8 rad/s, 11.5 μrad, and 200 g, respectively. The multi-DOF motions were successfully achieved by degenerating different vibration modes of the same ring structure.

Scaling a Hydraulic Motor for Minimally Invasive Medical Devices.

Aligned with the medical device industry's trend of miniaturization, academic and commercial researchers are constantly attempting to reduce device sizes. Many applications require miniature actuators (2 mm range) to perform mechanical work; however, biocompatible micromotors are not readily available. To that end, a hydraulic motor-driven cutting module that aims to combine cutting and drug delivery is presented. The hydraulic motor prototype developed has an outside diameter (OD) of ~4 mm (twice the target size) and a 1 mm drive shaft to attach a cutter. Four different designs were explored and fabricated using additive manufacturing. The benchtop experimental data of the prototypes are presented herein. For the prototype motor with fluid inlet perpendicular to the blades, the average angular velocity was 10,593 RPM at a flowrate of 3.6 mL/s and 42,597 RPM at 10.1 mL/s. This design was numerically modeled using 3D-transient simulations in ANSYS CFX (version 2022 R2) to determine the performance characteristics and the internal resistance of the motor. Simplified mathematical models were also used to compute and compare the peak torque with the simulation estimates. The viability of current design represents a crucial milestone in scaling the hydraulic motor to a 2 mm OD to power a microcutter.

A millipede-inspired miniature self-moving ultrasonic actuator with high carrying capability and nanometer resolution

To accomplish high carrying/positioning capability with compact structure, in this study, a miniature self-moving ultrasonic actuator (MSMUA) is developed by exciting a flexural traveling wave induced by dual longitudinal vibrations. Here, four lead-zirconate-titanite plates are bonded onto the bilateral ends of the bar-shaped vibrating body to efficiently generate the vibration. Interestingly, the MSMUA imitates the millipede in terms of the simple configuration and the operating principle. To test the validity, first, by using a Krimhertz-transmission-theory-based model, the key dimensions were adjusted to not only increase the driving-force-to-weight ratio but also make the elliptical motion shape close to the unity. Then, a prototype with the size of 87.5 × 9 × 9 mm3 and the weight of 15.67 g was fabricated, its moving/carrying/positioning performance was evaluated, and an array of MSMUAs was constructed to achieve flexible movement. At 105.44 kHz working frequency, the MSMUA in a tethered manner yielded the maximum payload of 433 g (equal to 27.7 times of its own weight), the maximum speed of 378 mm/s, and the maximum towing force of 0.4 N. Meanwhile, it crossed the gully 21 mm in width and climbed the slope of 7.4° Installed with an onboard circuit and 3.7 V batteries, the MSMUA provided the minimum step displacement of 19.2 nm. Moreover, the array of MSMUAs produced the turning movements (whose directions, angular speeds, and steering radii were adjustable) and the in-situ rotations. This study demonstrates the MSMUA's high carrying capability and nanometer resolution, and provides a new approach to design powerful ultrasonic actuators.

A Back-Drivable Rotational Force Actuator for Adaptive Grasping

In this paper, a back-drivable and miniature rotary series elastic actuator (RSEA) is proposed for robotic adaptive grasping. A compact arc grooves design has been proposed to effectively reduce the dimension of the RSEA system. The elastic elements could be reliably embedded in the arc grooves without any additional installation structures. The whole RSEA system is characterized as compact, miniature, and modular. The actuating force is controlled via a PI controller by tracking the deformation trajectory of the elastic elements. An underactuated finger mechanism has been adopted to investigate the effectiveness of the RSEA in robotic adaptive grasping. Results reveal that the underactuated finger mechanism could achieve adaptive grasping via the RSEA in a back-drive approach without the requirement of a fingertip force sensor. The RSEA could also exhibit an actuating compliance and a self-sensing characteristic. The actuating compliance characteristic helps in in guaranteeing the safety of human–robot interaction. The RSEA could estimate the external disturbance due to its self-sensing characteristic, which has the potential to replace the fingertip force sensor in grasping force perception applications.

Surface-Mounted Tilt Sensor Using Fiber Bragg Grating Technology for Engineered Slope Monitoring With Temperature Compensation

A surface-mounted tilt sensor was designed and fabricated to measure the inclination angle of engineered structures or slopes in two directions. The device utilizes two strain-sensitive FBGs for tilt angle measurement bi-directionally and one strain-free FBG to provide temperature compensation. In this work, a tilt sensor prototype was fabricated using a 3D printer, with a robust enclosure and a miniature actuator with dimensions of 115 x 65 x 30 mm and 45 x 20 x 3 mm, respectively. The device was first calibrated in the laboratory for tilt and temperature parameters. For tilt calibration, the device yields a sensitivity value of 0.0135 nm/° and 0.0123 nm/° for +x and -x directions. On the other hand, the device delivers a sensitivity value of 0.0105 nm/°C as the response to temperature changes. The tilt sensor was also tested for suitability in a real-field deployment where it was installed on a retaining wall and was left for 4 weeks. The field test data indicates no vertical displacement of the wall since the device exhibits zero inclination changes during the test period. This compact, robust, and easy-to-install tilt sensor has excellent potential for various geotechnical applications, mainly in landslide detections, ground movement, and engineered slope monitoring.

Design and dynamic analysis of a novel compound bending hollow piezoelectric beam miniature rotary actuator

In this paper, a miniature hollow piezoelectric beam rotary actuator is proposed and designed based on the compound bending vibration modes. The structure body is designed as an elastic hollow square beam with symmetrical piezoelectric patches attached at both ends, which directly eliminates the step of the frequency tuning. A conical rotor is driven by the hollow piezoelectric beam through the elliptical motions of the points on its inner surface. Based on the Timoshenko beam theory and Lagrange equation, the numerical continuum model is established to analyze the working mechanism. A prototype of the miniature rotary actuator with a size of 50 × 6 × 6 mm (2 mm through-hole) is manufactured and its performance under various excitation parameters is characterized in rotor speed experiments. The experimental results show that the maximum speed of the conical rotor is 913 rpm at the excitation voltage of 400 V. With a maximum load of 70.31 mN, the spherical rotor can achieve a speed of 450 rpm. The numerical results are in great agreement with the experimental results, so the output characteristics of the rotary actuator can be estimated. The simulation and test results demonstrate that the proposed rotary actuator has outstanding output performance and controllability. In addition, the simple structure design is easy to realize the frequency tuning and miniaturization.

A High-Power-Density Piezoelectric Actuator Operating in Bicycling Movement Mechanism

Comprehensive high-precision actuations are in growing demand to meet diversified needs in scientific and industrial fields. However, it is a great challenge for piezoelectric actuators with compact structure to guarantee high load capacity and wide velocity range (including fast motion velocity and high resolution) simultaneously. Herein, inspired by bionic methodology, a high-power-density bar-type linear piezoelectric ultrasonic actuator (LPUA) operating in the single second bending (<i>B₂</i>) mode with elaborate working principle is developed by imitating bicycle movement mechanism. The proposed <i>B₂</i>-LPUA actuator is simple, and easy for miniaturization without multimodal decoupling problem. Under only one-phase voltage drive, the miniature bar-type actuator can produce continuously bidirectional motions with the maximum driving velocity, minimum driving velocity, load, and output power of 211.2 mm&#x002F;s, 3.3 &#x03BC;m&#x002F;s, 5.4 N, and 218.3 mW, respectively, and the tested minimum step displacement is only 33 nm in open-loop control. Especially, its output power density (243 mW&#x002F;cm³ or 4.112 mW&#x002F;cm³.kHz) is at least twice larger than most reported LPUAs. The experimental results indicate that the proposed piezoelectric actuator with excellent actuation performances has broad application scenarios, and its bionic motion design method would have inspirational significance for creating new piezoelectric devices with more attractive properties.

Freeing the Animal Model: A Modular, Wirelessly Powered, Implantable Electronic Platform.

Fully implantable electronic devices in freely roaming animal models are useful in biomedical research, but their development is prohibitively resource intensive for many laboratories. The advent of miniaturized microcontrollers with onboard wireless data exchange capabilities has enabled cost-efficient development of myriad do-it-yourself electronic devices that are easily customizable with open-source software ( https://www.arduino.cc/ ). Likewise, the global proliferation of mobile devices has led to the development of low-cost miniaturized wireless power technology. The authors present a low-cost, rechargeable, and fully implantable electronic device comprising a commercially available, open-source, wirelessly powered microcontroller that is readily customizable with myriad readily available miniature sensors and actuators. The authors demonstrate the utility of this platform for chronic nerve stimulation in the freely roaming rat with intermittent wireless charging over 4 weeks. Device assembly was achieved within 2 hours and necessitated only basic soldering equipment. Component costs totaled $115 per device. Wireless data transfer and wireless recharging of device batteries was achieved within 30 minutes, and no harmful heat generation occurred during charging or discharging cycles, as measured by external thermography and internal device temperature monitoring. Wireless communication enabled triggered cathodic pulse stimulation of the facial nerve at various user-selected programmed frequencies (1, 5, and 10 Hz) for periods of 4 weeks or longer. This implantable electronic platform could be further miniaturized and expanded to study a vast array of biomedical research questions in live animal models. The clinical relevance of electrical stimulation in neural recovery remains controversial, and long-term neural stimulation in small animal models is challenging. We have developed a low-cost, fully implantable, wirelessly powered nerve stimulation device to facilitate further research in nerve stimulation in animal models.

Design of a Novel Flexible Robotic Laparoscope Using a Two Degrees-of-Freedom Cable-Driven Continuum Mechanism With Major Arc Notches

Abstract This article presents the design, development, and motion control of a novel flexible robotic laparoscope (FRL). The main structure of the FRL includes a two degrees-of-freedom (DOFs) continuum mechanism driven by two pairs of cable-pulley-driven systems, which are actuated by four miniature linear actuators. A constant-curvature model is employed on the kinematics modeling and analysis of the continuum mechanism with designed major arc notches. The bending control strategy of the continuum mechanism is proposed and realized based on its kinematics model and a feedforward compensation method considering its nonlinearity motion calibration with a suitable initial tension of the driven cables. Besides, the continuum mechanism is made of elastic nylon material through 3D printing technology. An experimental prototype is developed to test the effectiveness and feasibility of the FRL. The experimental results indicate that the FRL has good positioning accuracy and motion performance with potential applications in robot-assisted laparoscopic surgery.

A drug delivery device concept using a miniature tubular linear electromagnetic actuator: design, modeling and experimental validation

A drug delivery device concept using a miniature tubular linear electromagnetic actuator: design, modeling and experimental validation

A miniature impact drive mechanism with spatial interdigital structure

The development of compact precision instruments has raised the growing demand for miniature actuators. However, most miniature actuators failed to achieve balanced output performances, which limits the functionality of compact precision instruments. In this paper, a novel miniature impact drive mechanism (IDM) with balanced output performances is proposed. It adopts a spatial interdigital structure, which is helpful to decrease the whole size. The structure design and working principle are discussed in detail. Then, an IDM prototype with a size of 10 mm × 9.7 mm × 8 mm is fabricated, and its output performances are characterized. Experiment results indicate that the prototype has high motion stability in both forward and reverse motions. The maximum speeds of forward and reverse motions are 1.81 mm/s and 2.45 mm/s, respectively. While the resolution of forward and reverse motions reaches 12.55 nm and 8.77 nm, respectively. Besides, the maximum self-locking and thrust forces achieve 904 mN and 167.9 mN, respectively. The study provides a novel design of miniature IDMs, which could be beneficial to advance their practical applications.

Bio-Inspired Micro- and Nanorobotics Driven by Magnetic Field.

In recent years, there has been explosive growth in the number of investigations devoted to the development and study of biomimetic micro- and nanorobots. The present review is dedicated to novel bioinspired magnetic micro- and nanodevices that can be remotely controlled by an external magnetic field. This approach to actuate micro- and nanorobots is non-invasive and absolutely harmless for living organisms in vivo and cell microsurgery, and is very promising for medicine in the near future. Particular attention has been paid to the latest advances in the rapidly developing field of designing polymer-based flexible and rigid magnetic composites and fabricating structures inspired by living micro-objects and organisms. The physical principles underlying the functioning of hybrid bio-inspired magnetic miniature robots, sensors, and actuators are considered in this review, and key practical applications and challenges are analyzed as well.