Light Actuators Research Articles

Flexible and Precise Droplet Manipulation by a Laser-Induced Shape Temperature Field on a Lubricant-Infused Surface

Light actuation on a lubricant-infused surface (LIS) has attracted great attention because of its flexibility and remote control of droplet motion. However, to actuate a droplet on a LIS flexibly and precisely by light, the key issue is to control two degrees of freedom of the droplet motion in real time. In this paper, we propose a C-shape temperature field (CSTF) induced by rapid and selective laser irradiation on a LIS. The CSTF could not only manipulate a single droplet precisely and flexibly but also process multiple droplets automatically and orderly in real time. The mechanism showed that the droplet was confined by the Marangoni force in two orthogonal directions. For single droplet manipulation, the CSTF had the capability of correcting the off-track droplet motion. Moreover, the droplet motion, including rectilinear motion and curvilinear motion, could be precisely and flexibly controlled by the motion of the CSTF. For manipulation of multiple droplets, coalescence of multiple droplets was successfully achieved by triple rotating CSTFs. Such a method was applied in the detection of 5 μL of bovine serum albumin (BSA) by triggering chromogenic reactions automatically and orderly, which improved the efficiency of the whole process. We believe that this method is a significant candidate for intelligent droplet manipulation.

Numerical Investigation on Vibration Performance of Flexible Plates Actuated by Pneumatic Artificial Muscle

This paper theoretically introduced the feasibility of changing the vibration characteristics of flexible plates by using bio-inspired, extremely light, and powerful Pneumatic Artificial Muscle (PAM) actuators. Many structural plates or shells are typically flexible and show high vibration sensitivity. For this reason, this paper provides a way to achieve active vibration control for suppressing the oscillations of these structures to meet strict stability, safety, and comfort requirements. The dynamic behaviors of the designed plates are modeled by using the finite element (FE) method. As is known, the output force vs. contraction curve of PAM is nonlinear generally. In this present finite element model, the maximum forces provided by PAM in different air pressure are adopted as controlling forces for applying for the plate. The non-linearity between the output force and displacement of PAM is avoided in this study. The dynamic behaviors of plates with several independent groups of controlling forces are observed and studied. The results show that the natural frequencies of the plate can be varying and the max amplitude decreases significantly if the controlling forces are applied. The present work also demonstrates the potential of the PAM actuators as valid means for damping out the vibration of flexible systems.

Miniaturized Origami Robots: Actuation Approaches and Potential Applications

AbstractOrigami, a paper folding art, has inspired engineering applications in various fields for decades. It provides a simple approach to realize the transformation between simple 2D composite sheets and complex 3D functional structures. By integrating the origami concept with smart materials, a number of advanced origami robots have been developed with self‐deploying and programming capacities to respond to external environment stimuli. At present, miniaturized origami robots have demonstrated advantages in many‐profile applications, including bio‐inspired robotics, biomedical engineering, and environment monitoring. However, how to properly drive origami robots is a big challenge. In this paper, the investigation and analyses of the previous literature focus on the various actuations of miniaturized origami robots, including the magnetic, light, electric, swelling, motors, thermal, and other actuation methods. Finally, the article investigates applications of actuation methods for miniaturized origami robots with various functions, and discusses the challenges and opportunities in future applications.

Backstepping Sliding-Mode Control of Piezoelectric Single-Piston Pump-Controlled Actuator

A piston piezoelectric (PZT) pump has many advantages for the use of light actuators. How to deal with the contradiction between the intermittent oil supplying and position control precision is essential when designing the controller. In order to accurately control the output of the actuator, a backstepping sliding-mode control method based on the Lyapunov function is introduced, and the controller is designed on the basis of establishing the mathematical model of the system. The simulation results show that, compared with fuzzy PID and ordinary sliding-mode control, backstepping sliding-mode control has a stronger anti-jamming ability and tracking performance, and improves the control accuracy and stability of the piezoelectric pump-controlled actuator system.

Dynamic blinking in the head of hardyhead silverside fish

Dynamic light reflection can be used to provide an efficient tool for biological sensing of micro and nano-organisms. It is therefore interesting that evidence of dynamic light reflection can also be found in the animal kingdom and that there may be alternative methods of light control actuation. In this study, it is discovered that several features in the heads of hardyhead silverside fish, particularly those located around the edges of the iris, caused a blinking phenomenon using environmentally scattered light. Analysis of the blinking using recorded video of the fish iris revealed that circular cells that exist in the iris changed their light intensity at approximately 2 Hz. These cells, which are 5–10 μm in diameter, are normally blue. However, it is found that a distinct light intensity changed in 0.04 s, and additional green and yellow colors then overlapped with the blue.

Flow pulsation reduction of a single-piston piezoelectric pump based on elastic cavity group and unloading valve

A piston piezoelectric (PZT) pump has many advantages for the use of light actuators. How to deal with the contradiction between the piston amount and oil delivery quality is an essence when designing the pump. In order to depress the pressure pulsation and flow pulsation in a single-piston PZT pump, a two-stage attenuator is proposed. It involves an elastic cavity group and an unloading valve. Unsteady flow inside the pump is numerically calculated and analyzed to reveal its delivery characteristic in the whole pumping cycle. The distributing process of the passive valves is obtained through the dynamic mesh technique. Influences of key design and operation factors on the delivery performance of the pump are analyzed. The results indicate that the flexible cavity group and the unloading valve arranged at the delivery port can reduce the flow pulsation by 45%. The design can effectively provide stable flow for the actuator in a certain frequency range.

Effects of graphene nanoplatelets on bio-based shape memory polymers from benzoxazine/epoxy copolymers actuated by near-infrared light

Novel near-infrared (NIR) light-induced bio-based shape memory polymers (SMPs) were prepared from copolymers of vanillin/furfurylamine-based benzoxazine monomer (V-fa monomer) and epoxidized castor oil (ECO). Incorporation of graphene nanoplatelets (GNPs) as photothermal fillers into the copolymers provided shape memory properties under near-infrared (NIR) light actuation. The effects of GNP content on photothermal, thermal, dynamic mechanical, morphology, and shape memory properties of the bio-based benzoxazine/epoxy copolymers (V-fa/ECO copolymers) were investigated. The results showed that the addition of GNPs significantly improved the photothermal, thermal, and dynamic mechanical properties of the copolymers. The uniform dispersion of 3 wt% GNPs in the V-fa/ECO copolymers resulted in the highest shape memory performance with shape fixity of 92% and shape recovery of 99% upon NIR light actuation. The recovery time decreased with the increment of GNP content, and the V-fa/ECO copolymers filled with GNPs displayed good execution in the repeated fold-deploy, in which the shape fixity and shape recovery values were close to the original specimen. Therefore, the outstanding properties of V-fa/ECO copolymers filled with GNPs had a potential to be excellent SMPs under NIR actuation.

Simulation on an electro-hydrostatic actuator controlled by a high-pressure piezoelectric pump with a displacement amplifier

PurposeThe purpose of this paper is to provide a new hydrostatic actuator controlled by a piezoelectric piston pump and to reveal its characteristics.Design/methodology/approachIn this paper, a piezoelectric pump with passive poppet valves and hydraulic displacement amplifier is designed as a new control component in a hydrostatic actuator for high actuation capacity. A component-level mathematical model is established to describe the system characteristics. Simulation verification for cases under typical conditions is implemented to evaluate the delivery behavior of the pump and the carrying ability of the actuator.FindingsBy using the displacement amplifier and the passive distributing valves, simulation demonstrates that the pump can deliver flow rate up to 3 L/min, and the actuator controlled by this pump can push an object weighing approximately 50 kg. In addition, it is particularly important to decide a proper amplification ratio of the amplifier in the pump for better actuation performance.Originality/valueThe piezoelectric pump presented in this paper has its potential to light hydrostatic actuator. The model constructed in this paper is valid for characteristic analysis and performance evaluation of this pump and actuators.

A gravitational torque-compensated 2-DOF planar robotic arm design and its active control

Serial robot manipulators have their servo motors with reduction gears on the link joints. When it comes to hyper-redundant robots, this kind of joint actuation mechanism cannot be implemented since this makes hyper-redundant robots too heavy. Instead, cable driven mechanisms are preferred. However, the positioning accuracy is negatively affected by the cables. This paper addresses the positioning accuracy problem of cable driven hyper-redundant robots by employing a 2-DOF robotic arm whose modules are counter-balanced. While the actuators connected to the base actively do most of the work using cables and springs, light and compact actuators connected to the links produce precise motion. The method will result in compact, light and precise hyper-redundant robotic arms. The above-mentioned procedure governed by a control software including a 2D simulator developed is experimentally proved to be a feasible method to compensate the gravitational torque successfully.

Integrated W-Band Photoconductive Switches in SIW Technology

A novel approach for the design of millimeterwave (mmWave) substrate-integrated waveguide (SIW) switches is presented. The switch is based on controllable photoconductive elements (PEs), whose conductivity is modulated by a light source. The PE is integrated on the top SIW metal plate and provides either a short-circuit or transmission operation regime, depending on the actuation conditions. Due to the light actuation, the mmWave and dc control circuitry are naturally decoupled, which, in turn, makes the design low-loss and compact as compared to p-i-n diode and integrated circuit-based SIW switches implementations. We demonstrate two examples of SIW photoconductive switches (PSs) at W-band: single-pole single-throw (SPST) and single-pole double-throw (SPDT) PSs. Their operation principle, actuation, and parasitic radiation suppression are discussed. Measurements show the peak insertion loss of 0.9 and 2.2 dB, isolation better than 25 and 30 dB, and -10 dB impedance bandwidth of 21% and 15% for the SPST and SPDT PSs, respectively.

Injectable biomimetic hydrogels encapsulating Gold/metal–organic frameworks nanocomposites for enhanced antibacterial and wound healing activity under visible light actuation

• Biomimetic injectable hydrogel embedded with Au/MOF composites was synthesized. • Au nanoparticles could improve visible light-driven photocatalysis of ZIF-8. • The hydrogel kills bacteria under visible light while promoting wound healing. Antibiotic resistance of bacteria is one of the greatest threats to wound healing, which necessitates the need for alternative strategies to eradicate bacteria in the wound site. Taking advantage of the reactive oxygen species (ROS)-generating capability of photocatalytic semiconductor nanomaterials under light irradiation, here we report a biomimetic injectable double-network hydrogel using oxidized sodium alginate and carbohydrazide-modified methacrylated gelatin that mimics the extracellular matrix, which was further embedded with semiconductor-like metal–organic frameworks (MOFs) encapsulating noble metal nanoparticles (Au@ZIF-8). This composite design substantially improved the ROS generation under visible light actuation (>400 nm) compared with pristine ZIF-8, owing to its reinforced light absorption and charge carrier separation by the Au-mediated surface plasmon resonance (SPR) and Schottky junction. The composite hydrogels not only showed remarkable bactericidal activity against both E. coli and S. aureus , but also significantly accelerated wound healing at optimal safety. Altogether, this injectable double-network hydrogel could simultaneously provide antibacterial and pro-healing capabilities, which may have translational potential as wound dressing materials.

A Polymeric Bilayer Multi-Legged Soft Millirobot with Dual Actuation and Humidity Sensing.

There are numerous works that report wirelessly controlling the locomotion of soft robots through a single actuation method of light or magnetism. However, coupling multiple driving modes to improve the mobility of robots is still in its infancy. Here, we present a soft multi-legged millirobot that can move, climb a slope, swim and detect a signal by near-infrared irradiation (NIR) light or magnetic field dual actuation. Due to the design of the feet structure, our soft millirobot incorporates the advantages of a single actuation mode of light or magnetism. Furthermore, it can execute a compulsory exercise to sense a signal and analyze the ambience fluctuation in a narrow place. This work provides a novel alternative for soft robots to achieve multimode actuation and signal sensing.

A Polyoxometalate-Based Inorganic Porous Material with both Proton and Electron Conductivity by Light Actuation: Photocatalysis for Baeyer-Villiger Oxidation and Cr(VI) Reduction.

Two-dimensional (2D) crystalline porous materials with designable structures and high surface areas are currently a hot research topic in the field of proton- and electron-conducting materials, which provide great opportunities to orderly accommodate carriers in available spaces and to accurately understand the conducting path. The 2D dual-conductive inorganic framework [Co(H2O)6]2{[Co(H2O)4]4[WZn3(H2O)2(ZnW9O34)2]}·8H2O (Co6Zn5W19) is synthesized by combining [WZn3(H2O)2(ZnW9O34)2]12- (Zn5W19) and a Co(II) ion via a hydrothermal method. Due to the presence of a consecutive H-bonding network, electrostatic interactions, and packing effects between the framework and guest molecules, Co6Zn5W19 displays a high proton conductivity (3.55 × 10-4 S cm-1 under 98% RH and 358 K) by a synergistic effect of the combined components. Additionally, a photoactuated electron injection into the semiconducting materials is an important strategy for switching electronic conductivity, because it can efficiently reduce the frameworks without destroying the crystallinity. I-V curves of a tablet of Co6Zn5W19 in the reduced and oxidized states yield conductivities of 1.26 × 10-6 and 5 × 10-8 S cm-1, respectively. Moreover, Co6Zn5W19 is also successfully applied in the photocatalytic reduction of the toxic Cr(VI) metal ion by utilizing its excellent electronic storage capacity and Baeyer-Villiger (BV) oxidation in a molecular oxygen/aldehyde system.

Polarization-Modulated Multidirectional Photothermal Actuators.

Photothermal actuators have attracted increasing attention due to their ability to convert light energy into mechanical deformation and locomotion. This work reports a freestanding, multidirectional photothermal robot that can walk along a predesigned pathway by modulating laser polarization and on-off switching. Magnetic-plasmonic hybrid Fe3 O4 /Ag nanorods are synthesized using an unconventional templating approach. The coupled magnetic and plasmonic anisotropy allows control of the rod orientation, plasmonic excitation, and photothermal conversion by simply applying a magnetic field. Once the rods are fixed with desirable orientations in a bimorph actuator by magnetic-field-assisted lithography, the bending of the actuator can be controlled by switching the laser polarization. A bipedal robot is created by coupling the rod orientation with the alternating actuation of its two legs. Irradiating the robot by a laser with alternating or fixed polarization synergistically results in basic movement (backward and forward) and turning (including left-, right-, and U-turn), respectively. A complex walk along predesigned pathways can be potentially programmed by combining the movement and turning modes of the robots. This strategy provides an alternative driving mechanism for preparing functional soft robots, thus breaking through the limitations in the existing systems in terms of light sources and actuation manners.

A Versatile and Fully Integrated Hand-Held Device for Microfluidic-Based Biosensing: A Case Study of Plant Health Biomarkers

The development of a portable, Point-of-Need device to measure plant biomarkers in the field is reported. The system consists of a microcontroller-based hand-held device capable of reading photosensors at low signal levels (pA-nA) and driving light sources or pump actuators that couples to a microfluidic chip for performing colorimetric assays. The user interface is through a touchscreen and data is stored on-board in a memory card. Although robust and well-established bench-top instrumentation is available for these types of assays, many applications in the Agro-Food industry require portable systems that can make fast and inexpensive measurements in the field. We apply this system to the detection of Azelaic Acid (AzA), a known biomarker for plant health, in the nM regime. The developed system is versatile and can be applied to different types of ELISA, DNA and enzymatic based biosensing assays at the point-of-need, for plant, animal and human health applications.

Design and Fabrication of a Low-Cost Silicone and Water-Based Soft Actuator with a High Load-to-Weight Ratio.

Traditional actuators, such as motors as well as hydraulic or pneumatic artificial muscles, demonstrate excessive noise, a heavy weight, and a large size, which limit their practical application in many areas. Therefore, for many decades, scientists have worked to develop new types of silent, small, and light actuators. In this article, a novel soft actuator (actuator3) with a high load-to-weight ratio from silicone and a low-boiling liquid (ethanol: actuator3E or water: actuator3W) is presented and is compared with two actuators (actuator1 and actuator2) fabricated according to a method described in the literature. Compared with actuator1 and actuator2, actuator3 shows a larger volume expansion, output force, and load-to-weight ratio when heated. Owing to the weaker stability and repeatability of actuator3E, many different kinds of applications based on actuator3W are proposed, such as robotic hands and underwater rolling robots with color variations. The experimental results demonstrate that the method proposed in this article may be a viable alternative for fabricating low-cost soft actuators with high load-to-weight ratios that can be useful for future applications of soft robots.

Wireless Multistimulus‐Responsive Fabric‐Based Actuators for Soft Robotic, Human–Machine Interactive, and Wearable Applications

AbstractSoft actuators driven by pneumatic or electric means are heavy and clumsy with physical connections, which hinders their applications in human–machine interactive, wearable, and biomedical fields. Herewith, a light fabric bimorph actuator is reported that is driven wirelessly by optical, thermal, and magnetic energy sources. Being fabricated by laminating electrically conductive fabric and biaxially oriented polypropylene film, the actuators show a large bending curvature of 0.75 cm−1 with optical stimulus and 0.55 cm−1 with magnetic stimulus, a response time of 0.27 s with a bending angle of 100° to magnetic stimulus, more than twice faster than previously reported bimorph actuators. Their remarkable performance is attributed to the optimal structural design based on a verified Timoshenko model, electrothermal and optical properties of the conductive fabric coated by copper/nickel. It is greatly enhanced by the large difference of thermal expansion coefficients between the film and fabric. Various wireless controlled prototypes are demonstrated, including a soft gripper, soft kickers, and artificial blooming flowers, illustrating a new way to mass produce cost‐effective bimorph actuators via a simple, green, and fast approach for applications in robots, wearable, and functional textiles.

Photonic Thin Films Assembled from Amphiphilic Cellulose Nanofibrils Displaying Iridescent Full-Colors.

Self-assembly of nanoparticles (NPs) to form structural colors offers promising opportunities for developing electronic, optoelectronic, and magnetic devices. In this regard, we reported co-assembly of cellulose nanofibrils (CNFs) and graphene to produce colored thin films. We demonstrated that biomimetic iridescent "peacock feather"-like full-color thin films can be generated by simple evaporation of aqueous suspensions on a surface tension confined, optically symmetric indium tin oxide-coated polyethylene terephthalate substrate. Amphiphilic CNFs serve dual functions to attract hydrophobic graphene via van der Waals interactions and to disperse hydrophilically and anionically CNF-tethered graphene while regulating surface tension to induce capillary and Marangoni flows in the force fields and construct thickness variation during dewetting. These CNF-graphene thin films exhibit full-color patterns and function as tunable light and moisture actuators. This approach has high potential to be applied to assemble other metal or metal oxide NPs for fast, simple, and robust fabrication without involving any complex lithography and external fields.

Efficient Conversion of Light to Chemical Energy: Directional, Chiral Photoswitches with Very High Quantum Yields.

Photochromic systems have been used to achieve a number of engineering functions such as light energy conversion, molecular motors, pumps, actuators, and sensors. Key to practical applications is a high efficiency in the conversion of light to chemical energy, a rigid structure for the transmission of force to the environment, and directed motion during isomerization. We present a novel type of photochromic system (diindane diazocines) that converts visible light with an efficiency of 18 % to chemical energy. Quantum yields are exceptionally high with >70 % for the cis–trans isomerization and 90 % for the back‐reaction and thus higher than the biochemical system rhodopsin (64 %). Two diastereomers (meso and racemate) were obtained in only two steps in high yields. Both isomers are directional switches with high conversion rates (76–99 %). No fatigue was observed after several thousands of switching cycles in both systems.

Micro-rocket robot with all-optic actuating and tracking in blood

Micro/nanorobots have long been expected to reach all parts of the human body through blood vessels for medical treatment or surgery. However, in the current stage, it is still challenging to drive a microrobot in viscous media at high speed and difficult to observe the shape and position of a single microrobot once it enters the bloodstream. Here, we propose a new micro-rocket robot and an all-optic driving and imaging system that can actuate and track it in blood with microscale resolution. To achieve a high driving force, we engineer the microrobot to have a rocket-like triple-tube structure. Owing to the interface design, the 3D-printed micro-rocket can reach a moving speed of 2.8 mm/s (62 body lengths per second) under near-infrared light actuation in a blood-mimicking viscous glycerol solution. We also show that the micro-rocket robot is successfully tracked at a 3.2-µm resolution with an optical-resolution photoacoustic microscope in blood. This work paves the way for microrobot design, actuation, and tracking in the blood environment, which may broaden the scope of microrobotic applications in the biomedical field.