Actuation Speed Research Articles

Trajectory Generation for Flexible-Joint Space Manipulators

Space manipulator arms often exhibit significant joint flexibility and limited motor torque. Future space missions, including satellite servicing and large structure assembly, may involve the manipulation of massive objects, which will accentuate these limitations. Currently, astronauts use visual feedback on-orbit to mitigate oscillations and trajectory following issues. Large time delays between orbit and Earth make ground teleoperation difficult in these conditions, so more autonomous operations must be considered to remove the astronaut resource requirement and expand robotic capabilities in space. Trajectory planning for autonomous systems must therefore be considered to prevent poor trajectory tracking performance. We provide a model-based trajectory generation methodology that incorporates constraints on joint speed, motor torque, and base actuation for flexible-joint space manipulators while minimizing total trajectory time. Full spatial computer simulation results, as well as physical experiment results with a single-joint robot on an air bearing table, show the efficacy of our methodology.

Multichannel power electronics and magnetic nanoparticles for selective thermal magnetogenetics

Objective. We present a combination of a power electronics system and magnetic nanoparticles that enable frequency-multiplexed magnetothermal-neurostimulation with rapid channel switching between three independent channels spanning a wide frequency range. Approach. The electronics system generates alternating magnetic field spanning 50 kHz to 5 MHz in the same coil by combining silicon (Si) and gallium-nitride (GaN) transistors to resolve the high spread of coil impedance and current required throughout the wide bandwidth. The system drives a liquid-cooled field coil via capacitor banks, forming three series resonance channels which are multiplexed using high-voltage contactors. We characterized the system by the output channels’ frequencies, field strength, and switching time, as well as the system’s overall operation stability. Using different frequency–amplitude combinations of the magnetic field to target specific magnetic nanoparticles with different coercivity, we demonstrate actuation of iron oxide nanoparticles in all three channels, including a novel nanoparticle composition responding to magnetic fields in the megahertz range. Main results. The system achieved the desired target field strengths for three frequency channels, with switching speed between channels on the order of milliseconds. Specific absorption rate measurements and infrared thermal imaging performed with three types of magnetic nanoparticles demonstrated selective heating and validated the system’s intended use. Significance. The system uses a hybrid of Si and GaN transistors in bridge configuration instead of conventional amplifier circuit concepts to drive the magnetic field coil and contactors for fast switching between different capacitor banks. Series-resonance circuits ensure a high output quality while keeping the system efficient. This approach could significantly improve the speed and flexibility of frequency-multiplexed nanoparticle actuation, such as magnetogenetic neurostimulation, and thus provide the technical means for selective stimulation below the magnetic field’s fundamental spatial focality limits.

Microphase Separation‐Driven Sequential Self‐Folding of Nanocomposite Hydrogel/Elastomer Actuators

AbstractUntethered stimuli‐responsive soft materials with programmed sequential self‐folding are of great interest due to their ability to achieve task‐specific shape transformation with complex final configuration. Here, reversible and sequential self‐folding soft actuators are demonstrated by utilizing a temperature‐responsive nanocomposite hydrogel with different folding speeds but the same chemical composition. By varying the UV light intensity during the photo‐crosslinking of the nanocomposite hydrogel, different types of microstructures can be realized via phase separation mechanisms, which allow to control the folding speeds. The self‐folding structures are fabricated by integrating two dissimilar materials (i.e., a nanocomposite hydrogel and an elastomer) into hinge‐based bilayer structures via extrusion‐based 3D printing. It has been demonstrated that the folding kinetics can be accelerated by more than one order of magnitude due to the phase‐separated microstructure formed by the relatively weaker UV intensity (≈10 mW cm‐2) compared to the one formed by stronger UV intensity (≈100 mW cm‐2). 3D structures with sequential self‐folding capabilities are realized by prescribing actuation speeds and folding angles to specific hinges of the nanocomposite hydrogel. Sequential folding box and self‐locking latch structures are fabricated to demonstrate the ability to capture and hold objects underwater.

Continuum analysis of a soft bending actuator dynamics

Soft fiber-reinforced bending actuators are extensively used in different applications such as gripping mechanisms and rehabilitation robots. Modeling their dynamics is challenging due to their inherent nonlinearity that rises from both their material behavior and their geometrical features. This paper presents a continuum nonlinear model of the dynamic response of this actuator to inflation. The model is developed by considering the deformation to be hyperelastic and taking Rayleigh’s dissipative function into account. The deflection functions are obtained by solving the resulting differential equations using semi-inverse techniques. After fabricating a prototype and verifying the model experimentally in both time and frequency domains, it is further studied using bifurcation analysis concerning changes in the actuator’s geometrical parameters. Moreover, by analyzing the model in the frequency domain, a hardening behavior is observed in the system’s frequency response. In addition, the system’s response amplitude is inspected to decrease dramatically in higher frequencies, meaning that the actuator does not go back to its reference state owing to high actuation speed.

Poly(acrylic acid)-Based Hydrogel Actuators Fabricated via Digital Light Projection Additive Manufacturing

Electroactive polymers that exhibit controlled deformation under an applied electric field, either in liquid or air, have great potential as soft robotic actuators. However, materials for soft robotics currently face challenges, including slow response, high actuation potential, and a lack of underlying mechanistic understanding. Additionally, fabrication of soft robotic actuators with complex design features has historically been restricted by two-dimensional fabrication methods. In this work, we investigate cross-linked poly(acrylic acid)-based actuators prepared utilizing digital light projection (DLP), an additive manufacturing technique that enables fabrication of actuators with complex geometries. A series of photopolymerizable inks are prepared incorporating acrylic acid (monomer), trimethylolpropane trimethacrylate (cross-linker), and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator). Soft actuators are 3D-printed utilizing a commercial DLP 3D printer operating under 405 nm UV light. These 3D-printed actuators exhibit large deformation (up to 43°), high actuation speed (up to 1.08°/s), and stable actuation performance for bending cycles under relatively low actuation voltage (4–6 V). Factors such as acrylic acid content, cross-linker concentration, actuator thicknesses, and electric field strength are varied, and their impact on the 3D-printed actuators are evaluated and discussed. Lastly, a membrane valve actuator is fabricated, and its ability to open and close under applied potential is demonstrated.

Vibration suppression and fault‐tolerant control of an aerial refueling hose with multiple actuators

AbstractIn this paper, we propose an adaptive fault‐tolerant boundary vibration control approach for the flexible aerial refueling hose with variable length, variable speed, and multiple actuators. A distributed parameter system (DPS) is utilized to represent the dynamic behavior of the flexible refueling hose more precisely and accurately. Based on the established DPS model, we present a boundary vibration controller to suppress the vibration of the flexible refueling hose. In the controller, fault‐tolerant control with multiple actuators is considered to tackle the failure issues, and both multiplicative and additive failures are discussed in the fault situation. Then, by the Lyapunov direct method, we prove that the stability of the closed‐loop system is guaranteed under the proposed control approach. Numerical examples are presented to support the theoretical derivation.

Visual Stimuli-Based Dynamic Commands With Intelligent Control for Reactive BCI Applications

In this study, inconspicuous visual stimuli with hidden targets are considered as a new paradigm for reactive brain-computer interface (BCI) applications suitable for actuating a motorized system with a dynamic command from user. To drive the motor’s control signal level as close as possible to the targeted dynamic command via wireless transmission, an embeddable intelligent control scheme is introduced to improve the overall electroencephalography (EEG)-based decoding strategy of the BCI system. The proposed technique which can induce motivated attention only requires a single EEG channel, and the intelligent control scheme is constructed with a decoder consisting of a multilayer perceptron (MLP) neural network and a recursive digital Boxcar filter to suppress the influence of noise and ocular artifacts that are typically caused by user’s involuntary movements. Results from thirty subjects showed that the predictive ability of the BCI system was significantly improved via the proposed decoder compared to the performance of MLP models alone and those with low pass and Kalman filters which were two existing methods commonly used to alleviate the aforementioned perturbations in real-time applications. The BCI’s predictive ability could also be further enhanced by selecting a suitable stimulus to construct a generic MLP model for each gender due to notable performance disparities between male and female groups. The findings of this study will have the potential to increase the degree of freedom in reactive BCI applications particularly when embedded control systems with multiple actuator speeds or accelerations are desired such as those used to control mobile robotics.

Modeling, characterization and control of a piston-driven buoyancy system for a hybrid aerial underwater vehicle

This paper proposed the design and stability analysis of a piston variable buoyancy system (PVBS) with integration to a hybrid aerial underwater vehicle (HAUV). The HAUV must be lightweight and maneuverable to have sufficient endurance and reliability of operating in both underwater/air environments. To meet this crucial requirement, we designed a highly compact and lightweight PVBS to regulate the vehicle orientation and depth while operating underwater. A nonlinear motion model is firstly formulated to study the stability and control strategy of the PVBS.Frequency response analysis shows that the PVBS is inherently unstable. Therefore, a computationally affordable PID controller with a preset piston position is further developed to improve its phase response and hence make the PVBS more stable with anti-interference loss. Performance comparison between PID controllers with and without a preset piston position was conducted with simulations based on the nonlinear motion model. The effectiveness of the controller on gliding motion with different linear actuator speed are discussed based on extensive simulations. Field experiments of the designed PVBS with application to a novel HAUV named Nezha III are conducted. Results illustrate that, with the PVBS, Nezha III is able to maintain a desired vehicle pitch and heave velocity, as well as perform stable sawtooth gliding motion.

Achieving high speed of the stick-slip piezoelectric actuator at low frequency by using a two-stage amplification mechanism (TSAM).

The stick-slip piezoelectric actuator is a promising type for precision positioning with large stroke and high resolution; however, it is still challenging to achieve high motion speed at a relatively low driving frequency. To solve this problem, a novel two-stage amplification mechanism (TSAM) was designed, and correspondingly, a stick-slip piezoelectric actuator was developed. The structure, two-stage amplification principle, and motion processes of the designed actuator were addressed in detail, followed by analyzing the displacement amplification ratio and stress of TSAM via the elastic beam method and finite element method, respectively. Then, the actuator prototype was fabricated, and its output performances were tested under various experimental parameters. By comparative analysis with the actuator that only used the first-stage amplification hinge, the significant improvement in stepping displacement was verified when employing the TSAM. The resultant maximum motion speed was 20.05 mm/s, achieved under the locking force of 2 N, the input voltage of 100V, and the driving frequency of 700Hz. In addition, the developed actuator still maintained competitive motion resolution and loading capacity. The comparative analysis with some previous studies further indicated that the developed actuator with the TSAM had successfully achieved a relatively high motion speed at a relatively low driving frequency, which would be beneficial to the practical application.

High-Power Shape Memory Alloy Catapult Actuator for High-Speed and High-Force Applications

Nickel-Titanium (NiTi) based shape memory alloy (SMA) wires are already often used in industrial actuator applications. Their high energy density allows to build light-weight actuator systems with high forces using small installation spaces. Combined with the biocompatibility of NiTi, a huge field of applications can be covered by SMA actuated systems. In systems like emergency brakes or switch disconnectors, which require high forces as well as high actuation speed, the high-power capability of NiTi actuators is exploited. The presented work details the development and characterization of a giant power catapult demonstrator, that combines the high-speed and high-force capability of SMA wires. To illustrate the vast force, speed, and power potential of SMA wires, a bowling ball is launched from its resting position vertically into the air using SMA wires. For demonstration purposes a target altitude for the bowling ball of 500 mm is chosen. With the height and the overall accelerated mass given, an actuation force <i>F</i> &#x2245; 920 N is needed. The instantaneous energy release from the designed power source results in the targeted flight height and an overall peak power of <i>P</i> &#x2245; 0.5 MW.

A strong and tough gelatin/polyvinyl alcohol double network hydrogel actuator with superior actuation strength and fast actuation speed.

Hydrogels are widely used in actuators that are applied in numerous fields such as multifunctional sensors, soft robots, artificial muscles, manipulators and microfluidic valves, and yet their applications in soft robots and artificial muscles are often limited by low actuation strength and slow actuation speed. Here, we develop a hydrogel actuator with high actuation strength (contraction strength of 850 kPa), fast actuation speed (response time of 90 s) and high energy density (output working density of 72 kJ m-3) by introducing a storing-releasing elastic potential energy method into a double network hydrogel. The high actuation strength is owing to the double network hydrogel, which possesses a high elastic modulus of 1.3 MPa, fracture strength of 1.8 MPa, and fracture energy of 16 kJ m-2. The fast actuation speed is due to the storing-releasing elastic potential energy method, which stretches the hydrogel and locks the hydrogel at deformed shape under external stimuli to store the elastic potential energy and then makes the hydrogel contract rapidly under new stimuli to release the pre-stored energy. A capture actuator and a hand muscle actuator are fabricated to achieve strong and fast actuation. The hydrogel actuator has shown potential applications in soft robots and artificial muscles.

Cooling‐Accelerated Nanowire‐Nitinol Hybrid Muscle for Versatile Prosthetic Hand and Biomimetic Retractable Claw

AbstractAs strong and shape‐conformable as biological muscles, nitinol shape memory alloys (SMAs) artificial muscles have great merit when applied for bio‐inspired robots. However, the low bandwidth and slow actuation speed of SMAs due to their sluggish cooling have long been troublesome, limiting possible applications. Here, to expedite the cooling rate, a Cu nanowire forest is directly grown on the surfaces of 3D shaped SMA coil (SMAc) to increase the surface area by 15 times and boost thermal convection. As a result, the Cu nanowire forest grown SMA coil (CuNF‐SMAc) shows accelerated cooling compared to bare SMAc (B‐SMAc): the actuation speed of CuNF‐SMAc is 100% faster than that of bare SMAc (B‐SMAc) under natural cooling and 170% faster under forced‐air cooling. With this faster actuation, CuNF‐SMAc artificial muscles are employed in a versatile prosthetic hand to bend and flex fingers. The proposed prosthetic hand successfully demonstrates a series of sign language within 4 s for each letter, and rhythmically plays a grand piano. Moreover, unique retractable feline claws are mimicked which demonstrate a fully tunable frictional force just like how cats do it, expanding the potential of a cooling‐accelerated SMAc artificial muscle.

Fast Thermal Actuators for Soft Robotics.

Thermal actuation is a common actuation method for soft robots. However, a major limitation is the relatively slow actuation speed. Here we report significant increase in the actuation speed of a bimorph thermal actuator by harnessing the snap-through instability. The actuator is made of silver nanowire/polydimethylsiloxane composite. The snap-through instability is enabled by simply applying an offset displacement to part of the actuator structure. The effects of thermal conductivity of the composite, offset displacement, and actuation frequency on the actuator speed are investigated using both experiments and finite element analysis. The actuator yields a bending speed as high as 28.7 cm-1/s, 10 times that without the snap-through instability. A fast crawling robot with locomotion speed of 1.04 body length per second and a biomimetic Venus flytrap were demonstrated to illustrate the promising potential of the fast bimorph thermal actuators for soft robotic applications.

Energy Saving on a Full-Size Wheel Loader Through Variable Load Sense Margin Control

Abstract This paper presents the formulation of a variable load sense control strategy suitable to achieve power savings in hydraulic systems using postcompensated load sensing (LS) hydraulic control architectures. Such architecture is typical in off-road construction machinery. The paper also describes the application of the proposed control strategy referred to as variable load sensing margin (VLM) on a full-size wheel loader. The paper first presents the rationale for the proposed strategy, showing how the state-of-the-art LS architecture present in commercial machines has a margin for lowering the throttling losses present at the control valves. A feedforward controller, derived from an empirical study on a reference vehicle, is used to control the flow to the front-end loader functions. Test results show improvements of the hydraulic power consumption up to 45%, based on the commanded speed of each front-end loader actuator. The paper also describes a gain scheduling pressure feedback control strategy, which is used to allow controlling also functions that include priority. For the case of off-road vehicles, this is typically the steering function. The experimental results show good performances with an error in controlled velocity below 5%, which is achieved when the front-end loader functions are used concurrently with the steering.

Extended Analysis of a Valve-Controlled System with Multi-Chamber Actuator

This paper outlines an extended analysis on how multi-chamber actuators can improve the efficiency of valve-controlled systems. Resistive control is a major source of energy losses in valve-controlled systems that share the same pump to drive multiple loads. By combining different chambers, the load on multi-chamber actuators can be transformed into different pressure and flow rate levels. This allows the adaptation of its load to the loads on other actuators. This can lead to a reduction of resistive control energy losses that occur between pump and actuators when driven simultaneously. As a case study to highlight how the system efficiency can be improved, a load sensing system with a conventional and a multi-chamber actuator is analysed. The equations that describe the system steady state behaviour are presented to evaluate the effect of the load transformations on the system efficiency. A disadvantage of such architecture is the fact that load transformations result in different actuator speeds. To reduce this effect, a compensation factor for the command signal to the proportional valve is presented. The highlight from this paper is the potential for efficiency improvement enabled by the adoption of multi-chamber actuators in a valve-controlled architecture. Further research is required for the selection of number of chambers and their areas since they directly affect the system efficiency.

Dielectric Elastomer Actuators with Biphasic Ag–EGaIn Electrodes

A new electrode architecture for dielectric elastomer actuators (DEAs) is introduced in which a soft polyacrylate film is coated with a biphasic mixture of silver, indium, and gallium. This Ag–In–Ga coating functions as a soft electrode that is ultrathin, highly compliant, highly conductive, stretchable, and non‐smearing. Compared to carbon grease, sputter‐deposited metal coating, and particle‐filled conductive elastomers, this biphasic coating exhibits a unique combination of solid‐state integrity, extreme mechanical compliance, and low electrical resistivity. Herein, how DEAs with an Ag–In–Ga coating exhibit a 5× larger actuation speed compared to carbon‐coated dielectric films is shown. The influence of coating thickness on the mechanical stiffness and blocking force is also examined.

Application of Fuzzy Neural Network PID In Laser-guided Mortar Projectile

Based on the high control performance requirement of laser-guided mortar control system, the permanent magnet synchronous motor (PMSM) is adopted in this paper as the electromechanical actuator of the system, the mathematical model of the motor is analyzed, and the vector control technology is adopted to achieve precise control of position, speed and torque of the electromechanical actuator. Aiming at the characteristics of non-linearity, strong coupling and large parameter changes of the system in flight, an improved fuzzy neural network PID control method is proposed by combining the classical PID control algorithm with fuzzy control and neural network control algorithm to realize the real-time tuning and optimization of PID parameters. The mathematical model of the electromechanical actuator control system is established and simulated. The results show that the fuzzy neural network PID control has good tracking performance, small amplitude error, and strong adaptability to load changes.

Synthesis of a time-optimal control system for an extremal object

The paper presents the derivation of the synthesis method for the algorithm of the time-optimal controller for a third order dynamic system. A model with an extreme second-order transient response with delay was adopted as an object of research. The constant speed actuator is represented by an integrator. The synthesis is based on using the Pontryagin’s maximum principle and describing the dynamics of a system in the state space using canonical variables. The verification of the correctness of the result obtained by the theorem of Feldbaum A.A. on the number of switchings of the direction of movement of the regulating body during the control interval has been executed. To calculate the canonical state variables, it is proposed to use the position of the regulator, the controlled value and the derivative calculated from its values, measured on real objects.

Electro-Active and Photo-Active Vanadium Oxide Nanowire Thermo-Hygroscopic Actuators for Kirigami Pop-up.

Emerging technologies such as soft robotics, active biomedical devices, wearable electronics, haptic feedback systems, and healthcare systems require high‐fidelity soft actuators showing reliable responses under multi‐stimuli. In this study, the authors report an electro‐active and photo‐active soft actuator based on a vanadium oxide nanowire (VONW) hybrid film with greatly improved actuation performances. The VONWs directly grown on a cellulose fiber network increase the surface area up to 30‐fold and boost the hydrophilicity owing to the presence of oxygen‐rich functional groups in the nanowire surfaces. Taking advantage of the high surface area and hydrophilicity of VONWs, a soft thermo‐hygroscopic VONW actuator capable of being controlled by both light and electric sources shows greatly enhanced actuation deformation by almost 70% and increased actuation speed over 3 times during natural convection cooling. Most importantly, the proposed VONW actuator exhibits a remarkably improved blocking force of up to 200% compared with a bare paper actuator under light stimulation, allowing them to realize a complex kirigami pop‐up and to accomplish repeatable shape transformation from a 2D planar surface to a 3D configuration.

Large Stepwise Discrete Microsystem Displacements Based on Electrostatic Bending Plate Actuation

We present the design, fabrication, and experimental characterization of microsystems achieving large and stepwise discrete displacements. The systems consist of electrostatic bending plate actuators linked in a chain with increasing electrode gaps to allow a stepwise system displacement. A derived analytic transfer function permits to evaluate the influence of the system components on both the total and the stepwise system displacement. Based on calculation and simulation results, systems featuring 5, 8, 10, 13, and 16 steps are modeled and fabricated using a dicing-free SOI-fabrication process. During experimental voltage- and time-dependent system characterization, the minimum switching speed of the electrostatic actuators is 1 ms. Based on the guiding spring stiffness and the switching time, step-by-step and collective activations of the microsystems are performed and the system properties are derived. Furthermore, we analyze the influence of the number of steps on the total system displacement and present 16-step systems with a total maximum displacement of 230.7 ± 0.9 µm at 54 V.