Hybrid Actuator Research Articles

Soft hand with programmable grasping mode for dexterous manipulation

Many soft hands usually preprogram desired motions using oblique actuators, which limits their motion diversity and adaptability. To achieve high compliance and adaptability, this paper proposes a novel soft hand with a hybrid actuator system that can demonstrate both pure bending and helical motions. First, the structure and actuation system of the soft hand are presented. A direct-current motor is used to rotate the actuators. A pump is used to output sufficient torque to bend the soft hand. Second, a theoretical model and Finite Element Analysis (FEA) method are used to analyze the bending performance at various pressures. Then, a control method is proposed to regulate the helical radius of the soft hand in real time by adjusting the rotation angle and pressure simultaneously. Furthermore, experimental results verify the feasibility of programmable and dexterous grasping according to the shape of objects based on the independent control of bending and helical motions.

Unified recursive kinematics and statics modeling of a redundantly actuated series-parallel manipulator with high load/mass ratio

Construction robots with mobile systems are an integral part of automatic building processes. However, with the vigorous development of prefabricated buildings, traditional manipulators have progressively failed to satisfy the requirements of handling heavy materials on construction sites. Thus, this paper proposes a redundantly actuated series-parallel manipulator (RAS-PM). To explore the feasibility of applying the manipulator in construction tasks, this paper establishes the unified recursive kinematics and statics of the manipulator and verifies the validity and reliability of the theoretical modeling method through comprehensive numerical results. The prototype of the manipulator is developed and installed on a bionic hexapod construction robot. The test results demonstrate that the manipulator exhibits an excellent load/mass ratio in non-redundant actuation mode, and its load-carrying capacity can be further enhanced with the optimized force/position hybrid actuation. In the on-site test, the robot can freely switch between modes to handle horizontal and vertical states of materials, such as curtain walls and large panels, thereby contributing to modern prefabricated construction.

The Design and Investigation of Hybrid a Microfluidic Micromixer

Today, microfluidics has become a revolutionary interdisciplinary topic with considerable attention in a wide range of biotechnology applications. In this research work, a numerical investigation of a microfluidic micromixer is carried out using a hybrid actuation approach with different micropillar shapes and gaps. For this purpose, COMSOL Multiphysics v.5.2. is used with three different physics, such as thermoviscous acoustic physics to solve acoustic governing equations, laminar physics to solve fluid flow governing equations, and diluted transport species to solve mixing governing equations. The simulations were carried out at different Reynolds numbers such as 2, 4, 6, 8, 10, and 12 with an oscillation frequency of 15 kHz. The results were in the form of acoustic characteristics such as acoustic pressure, acoustic velocity, acoustic stream, mixing index, and fluid flow behaviour at various Reynolds numbers. The results revealed that the inclusion of micropillars improved the mixing performance and strength of the acoustic field, resulting in an improvement of the mixing performance compared to the case without micropillars. In addition, the mixing performance is also investigated at different Reynolds numbers, and a higher mixing index is investigated at lower Reynolds numbers. Moreover, it was also investigated that blade-shaped micropillars with 0.150 mm gaps deliver the best results compared to the other cases, and the maximum and minimum values of the mixing index are 0.97 and 0.72, respectively, at Reynolds number 2. The main reason behind this larger mixing index at low Reynolds numbers is due to the inclusion of micropillars that enhance the diffusion rate and contact area, leading to the homogenisation of the heterogeneous fluids in the microchamber. The obtained results can be extremely helpful for the design and modifications of a hybrid microfluidics micromixer.

Dynamics analysis and chatter control of a polishing and milling nonideal flexible manipulator

Some robots are designed to be lightweight and flexible, enabling them to access small and challenging paths in various applications. These features enable robots to collaborate with humans in performing specific production tasks. However,the movement of the flexible manipulator can become self-excited when handling a cutting tool on a workpiece, which can lead to a control problem. This article presents a control solution for lightweight robotic manipulators with rotating tools, such as polishing and milling, using smart actuators. The control discretization method is also introduced to facilitate integration into digital controllers. The paper starts by describing the governing equations of the non-ideal flexible manipulator for polishing and milling and analysing its dynamic behavior. Subsequently, models for the controllers of the DC motor-only actuators and the hybrid (shape memory alloy and DC motors) actuators were formulated using shape memory alloy and a suboptimal control scheme known as the discrete state-dependent Riccati equation. The coupled system was analysed dynamically, and it was observed that it exhibits chaotic behavior. The results suggest that incorporating smart actuators into the motor group of the system could decrease the positioning error of the manipulator and significantly reduce the oscillation of the robot’s end-effector.

Design and research of a piezoelectric-hydraulic hybrid actuation system with a half-wave resonator

Design and research of a piezoelectric-hydraulic hybrid actuation system with a half-wave resonator

Cross-Medium Time-Delay active vibration isolation method based on Voltage-Force hysteresis model

Micro-vibration significantly impacts spacecraft precision equipment operations, which can be resolved by using a piezoelectric actuator. The voltage-displacement relationship is the primary focus of current research on the hysteresis nonlinearity of piezoelectric actuators. Nevertheless, when tracking and controlling the acceleration/force signals of micro-vibration, control method based on the voltage-displacement introduces needless errors. In this paper, a cross-medium active vibration isolation control method based on voltage-force hysteresis model that can be utilised to track micro-vibration acceleration signals with high accuracy is proposed. The method exploits the slow transmission speed of vibration waves in a rubber medium to design a hybrid actuator mechanism containing a slow buffer medium and a piezoelectric actuator, and adopts a sliding mode control method to achieve accurate force control. Experiments demonstrated that compared with the vibration isolation control method based on voltage-displacement hysteresis model, the vibration isolation accuracy of the proposed method can be improved by 23.4%

Enhancing Flow Separation Control Using Hybrid Passive and Active Actuators in a Matrix Configuration

Efficient control of flow separation holds significant economic promise. This study investigates flow separation mitigation using an experimental platform featuring a combination of passive and active actuators arranged in a matrix configuration. The platform consists of 5 × 6 hybrid actuator units, each integrating a height-adjustable vortex generator and a micro-jet actuator. Inspired by the distributed pattern of V-shaped scales on shark skin, these actuator units are strategically deployed in a matrix configuration to reduce flow separation on a backward-facing ramp. Distributed pressure taps encircling the hybrid actuators monitor the flow state. Parametric analyses examine the effect of different control strategies. By adopting appropriate passive and active actuation patterns, effective pressure recovery on the ramp surface can be achieved. The most significant flow control outcome occurs when the actuators operate under combined active and passive excitation, harnessing the benefits of both control strategies. Particle image velocimetry (PIV) results confirm a notable reduction in flow separation under the best-controlled case. These findings suggest a promising future for flow control devices employing combined passive and active actuation in matrix-like configurations.

A Hybrid Actuator Model for Efficient Guided Wave based Structural Health Monitoring Simulations

Abstract Simulation has been recognized as a promising option to reduce the time and costs associated with determining Probability of Detection (POD) curves to demonstrate the performance of Guided Wave based Structural Health Monitoring (GW-SHM) systems. Time domain transient spectral finite element schemes have been used for large GW-SHM simulation campaigns, but the most common piezoelectric transducer model used for actuation, the pin force model, has limitations in terms of its range of validity. This is because the excitation frequency for the pin force model has only been validated far below the first electromechanical resonance frequency of the piezoelectric transducer mainly due to not considering the normal stress and dynamics of the transducer. As a result, the value of simulation tools for performance demonstrations may be limited. To address this limitation, this paper introduces a Hybrid Actuator Model that integrates frequency-dependent complex interfacial stresses in both the shear and normal directions, computed using finite elements. These surface stresses are compatible with time domain transient spectral finite element schemes, enabling their seamless integration without compromising the required performance for conducting intensive simulation campaigns. The proposed hybrid actuator model undergoes validation through a combination of simulation and experimental studies. Additionally, a comprehensive parametric study is conducted to assess the model's validity across a wide range of excitation frequencies. The results demonstrate the accurate representation of the transduction signal above the piezoelectric transducer's first free electromechanical resonance frequency.

Design of an actuator with bionic claw hook–suction cup hybrid structure for soft robot

To improve the adaptability of soft robots to the environment and achieve reliable attachment on various surfaces such as smooth and rough, this study draws inspiration from the collaborative attachment strategy of insects, cats, and other biological claw hooks and foot pads, and designs an actuator with a bionic claw hook–suction cup hybrid structure. The rigid biomimetic pop-up claw hook linkage mechanism is combined with a flexible suction cup of a ‘foot pad’ to achieve a synergistic adhesion effect between claw hook locking and suction cup adhesion through the deformation control of a soft pneumatic actuator. A pop-up claw hook linkage mechanism based on the principle of cat claw movement was designed, and the attachment mechanism of the biological claw hooks and footpads was analysed. An artificial muscle-spring-reinforced flexible pneumatic actuator (SRFPA) was developed and a kinematic model of the SRFPA was established and analysed using Abaqus. Finally, a prototype of the hybrid actuator was fabricated. The kinematic and mechanical performances of the SRFPA and entire actuator were characterised, and the attachment performance of the hybrid actuator to smooth and rough surfaces was tested. The results indicate that the proposed biomimetic claw hook–suction cup hybrid structure actuator is effective for various types of surface adhesion, object grasping, and robot walking. This study provides new insights for the design of highly adaptable robots and biomimetic attachment devices.

An MRI-Conditional Flexible Endoscopic Robot with a Hydraulic Tendon-Driven Actuation System

This paper presents the conceptualization, mathematical modeling, and experimental validation of a magnetic resonance imaging (MRI)-conditional, flexible endoscopic robot for MRI-guided neurosurgery. The robotic assembly encompasses a straight rigid shaft, a tendon-driven steerable tip with two degrees of freedom, and a compact hybrid actuation system made of nonmagnetic modules. The robot’s small diameter, approximately 3 mm, allows for robot navigation through narrow cavities, such as nasal passages and the densely packed anatomy of the skull base. By filling the robot with deionized water, the MRI contrast of the robot can be improved, therefore enabling intra-operative tracking of the robot’s movement. In this paper, we present the design and fabrication process of the robotic system, kinematic analysis of the robot, and experimental studies to validate our model, characterize the robot, and test the feedback robot control. Furthermore, we demonstrate the MRI compatibility of the robot, along with the intra-operative tracking capability.

On the Actuation Technologies of Biomedical Microrobot: A Summarized Review

In recent years, wireless microrobots have gotten more attention due to their huge potential in the biomedical field, especially drug delivery. Microrobots have several benefits, including small size, low weight, sensitivity, and flexibility. These characteristics have led to microscale improvements in control systems and power delivery with the development of submillimeter-sized robots. Wireless control of individual mobile microrobots has been achieved using a variety of propulsion systems, and improving the actuation and navigation of microrobots will have a significant impact. On the other hand, actuation tools must be integrated and compatible with the human body to drive these untethered microrobots along predefined paths inside biological environments. This study investigated key microrobot components, including medical applications, actuation systems, control systems, and design schemes. The efficiency of a microrobot is impacted by many factors, including the material, structure, and environment of the microrobot. Furthermore, integrating a hybrid actuation system and multimodal imaging can increase the microrobot's navigation effect, imaging algorithms, and working environment. In addition, taking into account the human body's moving distance, autonomous actuating technology could be used to deliver microrobots precisely and quickly to a specific position using a combination of quick approaches.

SMA Wire Use in Hybrid Twisting and Bending/Extending Soft Fiber-Reinforced Actuators

Soft fiber-reinforced actuators have demonstrated significant potential across various robotics applications. However, the actuation motion in these actuators is typically limited to a single type of motion behavior, such as bending, extending, and twisting. Additionally, a combination of bending with twisting and extending with twisting can occur in fiber-reinforced actuators. This paper presents two novel hybrid actuators in which shape memory alloy (SMA) wires are used as reinforcement for pneumatic actuation, and upon electrical activation, they create a twisting motion. As a result, the hybrid soft SMA-reinforced actuators can select between twisting and bending, as well as twisting and extending. In pneumatic mode, a bending angle of 40° and a longitudinal strain of 20% were achieved for the bending/twisting and extending/twisting actuators, respectively. When the SMA wires are electrically activated by the Joule effect, the actuators achieved more than 90% of the maximum twisting angle (24°) in almost 2 s. Passive recovery, facilitated by the elastic response of the soft chamber, took approximately 10 s. The double-helical reinforcement by SMA wires not only enables twisting in both directions but also serves as an active recovery mechanism to more rapidly return the finger to the initial position (within 2 s). The resulting pneumatic–electric-driven soft actuators enhance dexterity and versatility, making them suitable for applications in walking robots, in-pipe crawling robots, and in-hand manipulation.

Force analysis of a soft-rigid hybrid pneumatic actuator and its application in a bipedal inchworm robot

AbstractThis paper systematically investigates a soft-rigid hybrid pneumatic actuator (SRHPA), which consists of a rigid-foldable twisting skeleton capable of a large range of helical motion and a soft bellows muscle with high linear driving force. Considering the unique varying-pitch helical motion of the foldable skeleton, the analytical model mapping the input force generated by the bellows muscle and output forces of the actuator is revealed and verified with a simulation of the force analysis. Prototypes of the actuator are developed by fabricating the twisting skeleton with multilayered aluminum composite panels and 3D-printing the bellows muscle with thermoplastic polyurethane (TPU) 95A filament. The static and dynamic performances of the prototypes are tested to validate the analytical modeling of output forces. Using the actuator as a module, a novel bipedal inchworm robot with four modules is developed and tested to demonstrate its adaptability in confined space by switching between the going-straight, the turning-around, and the rotating gaits. The hybrid actuator and the inchworm robot with zero onboard electronics have the potential to be deployed in extreme environments where pneumatically actuated systems are preferred over electrical machines and drives, such as in nuclear and explosive environments.

An Origami Continuum Manipulator with Modularized Design and Hybrid Actuation: Accurate Kinematic Modeling and Experiments

Herein, this study contributes significantly to the advancement of continuum manipulators in two main aspects. First, a modularization concept and a hybrid actuation scheme to create a novel origami continuum manipulator with exceptional deformability are introduced. Second, an accurate model and framework for the forward and inverse kinematic analysis of origami manipulators are proposed. Specifically, each origami manipulator module can achieve axial extension and bending deformation by coordinated actuation of shape memory alloy (SMA) and pneumatic muscles, and the manipulator's end is equipped with a deformable gripper based on waterbomb origami and actuated by SMA. Through careful consideration of the self‐weight and torque balance, an accurate kinematic model based on the Denavit–Hartenberg method is established, which enables one to effectively predict the reachable extreme positions and spatial poses of the manipulator and solve the inverse kinematics using a genetic algorithm. Comprehensive experiments are conducted to validate the design's rationality and model's accuracy . In these tests, the rich spatial configurations are not only demonstrated that can be achieved by integrating hybrid actuators with origami modules but also the accuracy and reliability of the kinematic model are confirmed, opening up possibilities for the advancement and application of origami‐inspired robotics in various fields.

A variable stiffness soft robotic manipulator based on antagonistic design of supercoiled polymer artificial muscles and shape memory alloys

This paper introduces a soft robotic manipulator with variable stiffness capability. A novel compact hybrid and antagonistic actuation method is proposed, inspired by the muscle structure of creatures/organs such as octopus and human wrist. The manipulator consists of three pairs of shape memory alloy (SMA) springs–supercoiled polymer (SCP) strings in an antagonistic configuration. Both SMA spring and SCP string are thermally actuated. When the two types of actuators are driven, they are tensioned to increase stiffness, and the variable stiffness feature of the manipulator is further amplified by the antagonistic configuration of the actuators. A kinematic modeling of the manipulator is conducted, extending the classic constant curvature approach to six-actuators case. The effectiveness of this hybrid antagonistic variable stiffness mechanism and in reducing hysteresis are demonstrated experimentally. The performance of the manipulator is further validated by integrating a three-finger gripper for grasping and an endoscope for monitoring at its end, showing the potential of the proposed design for application in minimally invasive surgery (MIS).

A Wrist-Inspired Magneto-Pneumatic Hybrid-Driven Soft Actuator with Bidirectional Torsion.

A novel wrist-inspired soft actuator, which is driven by a magneto-pneumatic hybrid system and based on a Kresling origami unit, is proposed. The geometric model, kinematic analysis model, and quasistatic analysis model of the Kresling origami unit are presented. A key focus is on the formulation and investigation of the variation in rotation angle using the kinematic analysis model. A wrist-inspired soft actuator is designed, and its quasistatic characteristics are validated through various experiments. The paper proposes an innovative magneto-pneumatic hybrid actuation method, capable of achieving bidirectional torsion. This actuation method is experimentally validated, demonstrating the actuator's ability to maintain 3 steady states and its capability for bidirectional torsion deformation. Furthermore, the paper highlights the potential of the Kresling origami unit in designing soft actuators capable of achieving large rotation angles. For instance, an actuator with 6 sides (n = 6) is shown to achieve a rotation angle of 239.5°, and its rotation ratio exceeds 277°, about twice the largest one reported in other literature. The actuator offers a practical and effective solution for bidirectional torsion deformation in soft robotic applications.

Electro-Chemo-Mechanical Coupling in Hierarchical Nanoporous Gold-Polypyrrole-Water Hybrids

Nanoporous (np) metals made by dealloying is a novel class of nanostructured materials that offers numerous functionalities, ranging from sensing, energy storage, to (electro-)catalysis and beyond. A substantial amount of research in np materials has been focused on np gold due to its excellent structural and chemical stability, adjustable pore size, high conductivity, biocompatibility, and easy fabrication process via free corrosion or electrochemical dealloying. A considerable number of studies have been conducted to investigate np gold infiltrated with an aqueous electrolyte [1]. In that way, the material is considered as a hybrid so that one can reversibly tune the gold surface state by manipulating the superficial charge densities or adsorbate coverages via the applied electric potential [1]. The above-mentioned approach results in a number of intriguing properties of np Au revealed upon electrode potential variation in aqueous electrolytes such as actuation [2, 3], sensing [4], tunable strength [5] and elastic modulus [6]. The behavior is well-studied in case of weak ion adsorption and surface oxidation.One of the promising methods towards further improvement of functional and mechanical properties of np metals was implemented by Roschning and Weissmueller [7]. It was shown that the actuation strain of np Au can be enhanced via electrodeposition of a conductive polymer polypyrrole (PPy) on the gold surfaces. The actuation strain of the np Au-PPy hybrids strongly scales with the PPy phase fraction. Moreover, Li et al. [8] observed variations of effective elastic modulus in np Au-PPy-water hybrids. Thus, introducing the conductive polymer into a pore space of the np metal yields a hybrid actuator with a significantly improved actuation amplitude and yield strength.Here, we employ PPy for surface functionalization of hierarchical (hc) np Au (Figure 1) to explore the impact of the conductive polymer coating on the functional behavior of the hierarchically structured np metals. Np metals with structural hierarchy made by dealloying [9] open up new opportunities for multifunctional hard-soft hybrids. The larger pores at the higher hierarchical level (characterized by diameters around 120 nm) can promote fast mass exchange, while nanopores at the lower hierarchy level (below 30 nm) provide a large surface area and high chemical activity. Actuation behavior of the hybrid materials was analyzed in situ in a dilatometer upon potential cycling in a 1 M HClO4 aqueous electrolyte. The elastic response was examined in situ in a dynamic mechanical analyzer in the same electrolyte. We revealed pronounced changes of the macroscopic length and Young’s modulus in response to the voltage-induced redox reactions of the polymer films at the np electrodes. In the contribution, we discuss the origin of the electro-chemo-mechanical coupling phenomena.[1] Shao et al., in Nanoporous Gold: From an ancient technology to a high-tech material. RSC (2012).[2] Kramer et al. Nano Lett., 4(5) 793 (2004).[3] Jin et al. Nano Lett., 10(1) 187 (2010).[4] Stenner et al., Adv. Funct. Mater. 26 (28), 5174 (2016).[5] Jin et al., Science 332, 1179 (2011.)[6] Mameka et al., Acta Mater. 76, 272 (2014).[7] Roschning et al., Adv. Mater. Interfaces, 2001415 (2020).[8] Li et al., Acta Mater., 212 (1), 116852 (2021).[9] Shi et al., Science 371, 1026 (2021).Figure 1. Scanning electron micrograph of hierarchical nanoporous Au-PPy hybrid microstructure. Figure 1

Macroscale Collagen‐Actomyosin Hybrid Actuator Built from Bioderived Materials (Adv. Funct. Mater. 51/2023)

Macroscale Collagen‐Actomyosin Hybrid Actuator Built from Bioderived Materials (Adv. Funct. Mater. 51/2023)

Wake characteristics of a balloon wind turbine and aerodynamic analysis of its balloon using a large eddy simulation and actuator disk model

Abstract. In the realm of novel technologies for generating electricity from renewable resources, an emerging category of wind energy converters called airborne wind energy systems (AWESs) has gained prominence. These pioneering systems employ tethered wings or aircraft that operate at higher atmospheric layers, enabling them to harness wind speeds surpassing conventional wind turbines' capabilities. The balloon wind turbine is one type of AWESs that utilizes the buoyancy effect to elevate the turbine to altitudes typically ranging from 400 to 1000 m. In this paper, the wake characteristics and aerodynamics of a balloon wind turbine were numerically investigated for different wind scenarios. Large eddy simulation, along with the actuator disk model, was employed to predict the wake behavior of the turbine. To improve the accuracy of the simulation results, a structured grid was generated and refined by using an algorithm to resolve about 80 % of the local turbulent kinetic energy in the wake. Results contributed to designing an optimized layout of wind farms and stability analysis of such systems. The capabilities of the hybrid large eddy simulation and actuator disk model (LES–ADM) when using the mesh generation algorithm were evaluated against the experimental data on a smaller wind turbine. The assessment revealed a good agreement between numerical and experimental results. While a weakened rotor wake was observed at the distance of 22.5 diameters downstream of the balloon turbine, the balloon wake disappeared at about 0.6 of that distance in all the wind scenarios. Vortices generated by the rotor and balloon started to merge at the tilt angle of 10∘, which intensified the turbulence intensity at 10 diameters downstream of the turbine for the wind speeds of 7 and 10 m s−1. By increasing the tilt angle, the lift force on the wings experienced a sharper increase with respect to that of the whole balloon, which signified a controlling system requirement for balancing such an extra lift force.

Leaping fishbot by combustion and propulsion hybrid actuation

AbstractAutonomous underwater vehicles have been extensively developed in the past decades and deployed for various ocean research activities. While the leaping‐out motions of underwater creatures have motivated the development of underwater robots with the motion ability to jump out of water, the dynamics of such jumping robots have not been fully described. In this study, we developed a leaping fishbot, a flying fish‐inspired underwater soft robot that can leap out of the water and further sail on the surface using the combustion and propulsion hybrid actuation. Specifically, the fishbot uses the transient driving method, in which a premixed oxygen–propane gas generates an instant pushing impulse to launch the robot out of the water at a transiently high speed while the attached jetting propellers provide a sustained thrust as it swims on the water surface at a stable velocity. A series of flume experiments and solid–fluid hybrid computational fluid dynamics numerical simulations were conducted to study the kinematic performance of the robot. Experimental results established a quantitative relationship between the kinematic performance, gas amount, and launch angle. The numerical results accurately predicted the water–air multiphase jumping motions, the numerical result of kinematic was significantly agreeing with the experimental results, the error in the horizontal direction is less than 15%, and that in the vertical direction is less than 10%. We further analyzed the flow field generated by the leaping fishbot to gain a better understanding of the velocity and vortex distribution around it. Our research findings provide valuable insights into bionic application of underwater robots in the future.