Showing papers on "Actuator published in 2021"
TL;DR: In this paper, a sliding-mode surface analysis for MIMO underactuated systems is presented, and the asymptotic stability of the system equilibrium point is strictly proven based on the composite surfaces.
Abstract: In the field of modern industrial engineering, many mechanical systems are underactuated, exhibiting strong nonlinear characteristics and high flexibility However, the lack of control inputs brings about many difficulties for controller design and stability/convergence analysis Additionally, some unavoidable practical issues, eg, plant uncertainties and actuator deadzones, make the control of underactuated systems even more challenging Hence, with the aid of elaborately constructed finite-time convergent surfaces, this article provides the first solution to address the control problem for a class of multi-input-multi-output (MIMO) underactuated systems subject to plant uncertainties and actuator deadzones Specifically, this article overcomes the main obstacle in sliding-mode surface analysis for MIMO underactuated systems, that is, by the presented analysis method, the asymptotic stability of the system equilibrium point is strictly proven based on the composite surfaces In addition, the unknown parts of the actuated/unactuated dynamic equations and actuator deadzones can be simultaneously handled, which is important for real applications Furthermore, we apply the proposed method to two kinds of typical underactuated systems, that is: 1) tower cranes and 2) double-pendulum cranes, and implement a series of hardware experiments to verify its effectiveness and robustness
114 citations
TL;DR: In this article, an adaptive fuzzy fault-tolerant control strategy is introduced to deal with the difficulties associated with the actuator faults and external disturbance, and a modified performance function, which is called the finite-time performance function (FTPF), is presented.
Abstract: In this article, finite-time-prescribed performance-based adaptive fuzzy control is considered for a class of strict-feedback systems in the presence of actuator faults and dynamic disturbances. To deal with the difficulties associated with the actuator faults and external disturbance, an adaptive fuzzy fault-tolerant control strategy is introduced. Different from the existing controller design methods, a modified performance function, which is called the finite-time performance function (FTPF), is presented. It is proved that the presented controller can ensure all the signals of the closed-loop system are bounded and the tracking error converges to a predetermined region in finite time. The effectiveness of the presented control scheme is verified through the simulation results.
103 citations
TL;DR: An observer-based adaptive dynamic surface control (DSC) strategy is proposed for nonlinear nonstrict-feedback systems with time-varying disturbance, event-triggered mechanism, and actuator failures in this paper.
Abstract: An observer-based adaptive dynamic surface control (DSC) strategy is proposed for nonlinear nonstrict-feedback systems with time-varying disturbance, event-triggered mechanism, and actuator failures in this paper. Fuzzy logic systems are implemented to construct an observer to estimate the unmeasured states. The DSC method is exploited to solve the issue of “explosion of complexity” with the backstepping control technique. The constructed event-triggered mechanism can avoid the waste of communication resources. The barrier Lyapunov functions are utilized to address the problem of output constraint. It is demonstrated that the reference signals can be well tracked by the system output and all closed-loop signals remain semi-globally uniformly ultimately bounded. Two examples illustrate the effectiveness of the constructed controller.
103 citations
TL;DR: In this article, an adaptive fault tolerant control strategy is developed to suppress the vibrations of the flexible panel in the course of the attitude stabilization, and a Lyapunov-based stability analysis is conducted to determine whether the system energies, angular velocities and transverse deflections, remain bounded and asymptotically decay to zero in the case of infinite number of actuator failures.
Abstract: In this paper, we address simultaneous control of a flexible spacecraft’s attitude and vibrations in a three-dimensional space under input disturbances and unknown actuator failures. Using Hamilton’s principle, the system dynamics is modeled as an infinite dimensional system captured using partial differential equations. Moreover, a novel adaptive fault tolerant control strategy is developed to suppress the vibrations of the flexible panel in the course of the attitude stabilization. To determine whether the system energies, angular velocities and transverse deflections, remain bounded and asymptotically decay to zero in the case wherein the number of actuator failures is infinite, a Lyapunov-based stability analysis is conducted. Finally, extensive numerical simulations are performed to demonstrate the performance of the proposed adaptive control strategy.
103 citations
TL;DR: This article proposes a fault-tolerant compensation control approach against nonlinearity, simultaneous additive, and multiplicative actuator faults in Markov jump systems using the fuzzy logic system (FLS) to approximate the nonlinear functions, which have no available knowledge.
Abstract: This article proposes a fault-tolerant compensation control approach against nonlinearity, simultaneous additive, and multiplicative actuator faults in Markov jump systems. In this article, we first exploit the fuzzy logic system (FLS) to approximate the nonlinear functions, which have no available knowledge. Then, by utilizing the adaptive backstepping technique, a FLS-based adaptive fault-tolerant compensation controller is proposed, which can completely compensate for the adverse effects, arising from the additive actuator faults, the multiplicative actuator faults, and the mismatched nonlinearity simultaneously. The stability of the closed-loop system can be guaranteed by the proposed FLS-based adaptive controller with the adaptation laws. The novelty of this article lies in the fact that the additive and multiplicative actuator faults, and mismatched nonlinearity are considered simultaneously. Besides, the renown sliding mode control approach has limitations to deal with the FTC problem considered in this article because the considered nonlinearity is a mismatched one. The proposed control approach can cope with the challenging case. Finally, a practical wheeled mobile manipulator system is used to demonstrate the effectiveness and validity of the proposed approach.
98 citations
TL;DR: In this article, the authors investigated the tracking control problem of marine surface vessels (MSVs) in the presence of uncertain dynamics and external disturbances, and proposed a novel event-triggered indirect neuroadaptive fault-tolerant control scheme.
Abstract: This paper investigates the tracking control problem of marine surface vessels (MSVs) in the presence of uncertain dynamics and external disturbances. The facts that actuators are subject to undesirable faults and input saturation are taken into account. Benefiting from the smoothness of the Gaussian error function, a novel saturation function is introduced to replace each nonsmooth actuator saturation nonlinearity. Applying the hand position approach, the original motion dynamics of underactuated MSVs are transformed into a standard integral cascade form so that the vector design method can be used to solve the control problem for underactuated MSVs. By combining the neural network technique and virtual parameter learning algorithm with the vector design method, and introducing an event triggering mechanism, a novel event-triggered indirect neuroadaptive fault-tolerant control scheme is proposed, which has several notable characteristics compared with most existing strategies: 1) it is not only robust and adaptive to uncertain dynamics and external disturbances but is also tolerant to undesirable actuator faults and saturation; 2) it reduces the acting frequency of actuators, thereby decreasing the mechanical wear of the MSV actuators, via the event-triggered control (ETC) technique; 3) it guarantees stable tracking without the a priori knowledge of the dynamics of the MSVs, external disturbances or actuator faults; and 4) it only involves two parameter adaptations--a virtual parameter and a lower bound on the uncertain gains of the actuators--and is thus more affordable to implement. On the basis of the Lyapunov theorem, it is verified that all signals in the tracking control system of the underactuated MSVs are bounded. Finally, the effectiveness of the proposed control scheme is demonstrated by simulations and comparative results.
93 citations
TL;DR: A novel fault-tolerant and antiattack control method is proposed, which enables the system to achieve the security control objective even in an insecure network and physical environment.
Abstract: This paper investigates the adaptive event-triggered secure control design problem for a class of stochastic nonlinear high-order multi-agent systems (MASs) subject to denial-of-service (DoS) attacks and actuator faults. The considered systems contain not only unknown random interference terms but also general nonlinear functions that are not required to be globally Lipschitz, in contrast to most of the existing results in the area. To solve the problem of wasted communication resources, the control signal with the relative threshold strategy is designed via the event-triggered control (ETC) technique. As a class of cyber-physical systems (CPSs), the securities of MASs are vulnerable to actuator faults and DoS attacks. When the system suffers from coupled DoS attacks and actuator failures, its performance will deteriorate rapidly and even the controlled system will collapse. To overcome this difficulty, a novel fault-tolerant and anti-attack control method is proposed, which enables the system to achieve the security control objective even in an insecure network and physical environment. The stability analysis of the system is given by combining the adaptive backstepping recursive design process with stochastic Lyapunov stability theory. It is demonstrated that all the signals of the closed-loop systems are semi-globally uniformly ultimately bounded (SGUUB) in probability. Finally, a simulation example is given to illustrate the effectiveness and advantages of the presented scheme.
78 citations
TL;DR: Fractional Lyapunov stability criterion is adopted to prove the convergence of the developed proposed controller even in the presence of actuator faults.
Abstract: This paper studies the adaptive control problem for a class of uncertain fractional nonlinear systems with actuator faults, where the total number of failures is allowed to be infinite. A compensating term in a smooth function form of a conventional control law is introduced to compensate for the actuator faults. After the introduction of fractional-order adaptation laws, an adaptive controller is designed by using a modified backstepping technique. Fractional Lyapunov stability criterion is adopted to prove the convergence of the developed proposed controller even in the presence of actuator faults. Finally, a simulation example of fractional-order Chua–Hartley’s system is given to verify the effectiveness of the proposed fault-tolerant control scheme.
69 citations
TL;DR: In this article, a review of the evolution of high strain Na0.5Bi0.3-based lead-free piezoceramics and their multilayer actuators has been explored.
68 citations
25 Jan 2021
TL;DR: An electrical plant-based actuator is reported that uses a conformable electrical interface as an electrical modulating unit and a Venus flytrap as an actuating unit and accurate on-demand actuation is possible, with response times that can be tuned to 1.3 s and a power input of 10−5 W.
Abstract: Owing to their adaptive interfacial properties, soft actuators can be used to perform more delicate tasks than their rigid counterparts. However, traditional polymeric soft actuators rely on energy conversion for actuation, resulting in high power input or slow responses. Here we report an electrical plant-based actuator that uses a conformable electrical interface as an electrical modulating unit and a Venus flytrap as an actuating unit. Using frequency-dependent action-potential modulation, accurate on-demand actuation is possible, with response times that can be tuned to 1.3 s and a power input of only 10−5 W. The actuator can be wirelessly controlled using a smartphone. It can also be installed on a range of platforms (including a finger and a robotic hand) and can be used to grasp thin wires and capture moving objects. By using a conformable electrical interface as an electrical modulating unit and a Venus flytrap as an actuating unit, a biohybrid actuator can be created that is power efficient and responsive, and it can be wirelessly controlled via a smartphone.
67 citations
TL;DR: This article presents a new output feedback control method to accomplish rapid jib and trolley positioning and payload sway suppression, based on the original dynamic models without any linearization manipulations.
Abstract: Tower cranes are a class of important and useful tools for the transportation of large cargoes, especially in high building construction. Moreover, the combination of jibs’ rotational movements and trolleys’ translational movements can fulfill three-dimensional payload transportation in a huge outdoor workspace. However, complicated dynamics and different unfavorable environmental conditions in practice make the effective control of tower cranes very challenging. In this article, based on the original dynamic models without any linearization manipulations, we present a new output feedback control method to accomplish rapid jib and trolley positioning and payload sway suppression. In particular, the velocity signals are accurately obtained by an elaborately designed observer, instead of numerical differentiation manipulations to the measurable output variables (which may distort the original velocities to some extent). Based on the velocity estimates, the suggested controller can also handle uncertain friction. Additionally, the actuator constraints are fully considered during controller design, i.e., the calculated control inputs are both within the permitted ranges, thereby avoiding actuator saturation and degrading the control performance. For the entire closed-loop system, including the proposed controller, the state observer, and tower cranes, the asymptotic stability is strictly proven by Lyapunov-based techniques. Finally, some comparative and robustness verifications are implemented by hardware experiments.
01 Mar 2021
TL;DR: The self‐controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.
Abstract: Herein, a novel tactile sensing device (SensAct) with a soft touch/pressure sensor seamlessly integrated on a flexible actuator is presented. The squishy touch sensor is developed with custom‐made graphite paste on a tiny permanent magnet, encapsulated in Sil‐Poxy, and the actuator (15 μ‐thick coil) is fabricated on polyimide by Lithographie Galvanoformung Abformung (LIGA) micromolding method. The actuator can operate in two modes (expansion and contraction/squeeze) and two states (vibration and nonvibration). The sensor was tested with up to 12 N applied forces and exhibited ≈70% average relative resistance variation (ΔR/Ro), ≈0.346 kPa−1 sensitivity, and ≈49 ms response time with excellent repeatability (≈12.7% coefficient of variation) at 5 N. During simultaneous sensing and actuation, the modulation of coil current, due to ΔR/Ro (≈14% at 2 N force) in the sensor, allows the close loop control (ΔI/Io ≈385%) of expansion/contraction (≈69.8 μm expansion in nonvibration state and ≈111.5 μm peak‐to‐peak in the vibration state). Finally, the soft sensor is embedded in the 3D‐printed fingertip of a robotic hand to demonstrate its use for pressure mapping along with remote vibrotactile stimulation using SensAct device. The self‐controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.
TL;DR: In this paper, the physical basis underlying the operation of dielectric elastomer actuators is described, starting with a simple linear analysis, followed by nonlinear Newtonian and energy approaches necessary to describe large strain characteristics of actuators.
Abstract: Dielectric elastomer actuators (DEAs) are soft, electrically powered actuators that have no discrete moving parts, yet can exhibit large strains (10%–50%) and moderate stress (∼100 kPa). This Tutorial describes the physical basis underlying the operation of DEA's, starting with a simple linear analysis, followed by nonlinear Newtonian and energy approaches necessary to describe large strain characteristics of actuators. These lead to theoretical limits on actuation strains and useful non-dimensional parameters, such as the normalized electric breakdown field. The analyses guide the selection of elastomer materials and compliant electrodes for DEAs. As DEAs operate at high electric fields, this Tutorial describes some of the factors affecting the Weibull distribution of dielectric breakdown, geometrical effects, distinguishing between permanent and “soft” breakdown, as well as “self-clearing” and its relation to proof testing to increase device reliability. New evidence for molecular alignment under an electric field is also presented. In the discussion of compliant electrodes, the rationale for carbon nanotube (CNT) electrodes is presented based on their compliance and ability to maintain their percolative conductivity even when stretched. A procedure for making complaint CNT electrodes is included for those who wish to fabricate their own. Percolative electrodes inevitably give rise to only partial surface coverage and the consequences on actuator performance are introduced. Developments in actuator geometry, including recent 3D printing, are described. The physical basis of versatile and reconfigurable shape-changing actuators, together with their analysis, is presented and illustrated with examples. Finally, prospects for achieving even higher performance DEAs will be discussed.
TL;DR: In this paper, an adaptive fuzzy hierarchical sliding mode control method was proposed to deal with the control problem for uncertain under-actuated switched nonlinear systems with actuator control in the presence of uncertain underactuated switches.
Abstract: This paper aims at putting forward an adaptive fuzzy hierarchical sliding mode control method to deal with the control problem for uncertain under-actuated switched nonlinear systems with actuator ...
TL;DR: An adaptive SMC law is proposed to guarantee that the estimation states and errors can reach to the sliding surfaces, and the stochastic admissibility of the singular S-MJSs can be ensured.
Abstract: The adaptive sliding mode control (SMC) problem is addressed for singular semi-Markovian jump systems (S-MJSs) against actuator attacks, in which the transition rates rely on the random sojourn time and are not constant, and the system states are unavailable. Moreover, the vulnerability of control signals transmitted via communication network means that the actuators may receive the attacked control signals. For the sake of reducing the effect of actuator attacks, the neural network technique is used to approximate the false information injected by adversaries. Meanwhile, a sliding mode observer is introduced to estimate the unmeasured states. An adaptive SMC law is proposed to guarantee that the estimation states and errors can reach to the sliding surfaces, and the stochastic admissibility of the singular S-MJSs can be ensured. In the end, an example is applied to illustrate the method in this paper.
TL;DR: In this article, a fault-tolerant consensus control of a general nonlinear multi-agent system subject to actuator faults and disturbed and faulty networks is proposed by using neural network (NN) and adaptive control techniques.
Abstract: This article addresses the problem of fault-tolerant consensus control of a general nonlinear multiagent system subject to actuator faults and disturbed and faulty networks. By using neural network (NN) and adaptive control techniques, estimations of unknown state-dependent boundaries of nonlinear dynamics and actuator faults, which can reflect the worst impacts on the system, are first developed. A novel NN-based adaptive observer is designed for the observation of faulty transformation signals in networks. On the basis of the NN-based observer and adaptive control strategies, fault-tolerant consensus control schemes are designed to guarantee the bounded consensus of the closed-loop multiagent system with disturbed and faulty networks and actuator faults. The validity of the proposed adaptively distributed consensus control schemes is demonstrated by a multiagent system composed of five nonlinear forced pendulums.
TL;DR: In this article, an adaptive fault-tolerant control design for a flexible Timoshenko arm considering the effects of actuator failures, backlash-like hysteresis, and external disturbances was proposed.
TL;DR: In this article, an adaptive neural-network command-filtered tracking control scheme for nonlinear systems with multiple actuator constraints is proposed, where the boundedness of all variables is guaranteed and the output tracking error fluctuates near the origin within a small bounded area.
Abstract: This article proposes an adaptive neural-network command-filtered tracking control scheme of nonlinear systems with multiple actuator constraints. An equivalent transformation method is introduced to address the impediment from actuator nonlinearity. By utilizing the command filter method, the explosion of complexity problem is addressed. With the help of neural-network approximation, an adaptive neural-network tracking backstepping control strategy via the command filter technique and the backstepping design algorithm is proposed. Based on this scheme, the boundedness of all variables is guaranteed and the output tracking error fluctuates near the origin within a small bounded area. Simulations testify the availability of the designed control strategy.
TL;DR: It is proved that the proposed fuzzy adaptive two-bit-triggered control for uncertain nonlinear systems with actuator failures and dead-zone constraint can guarantee the system tracking performance and all the signals are bounded.
Abstract: This article investigates a fuzzy adaptive two-bit-triggered control for uncertain nonlinear systems with actuator failures and dead-zone constraint. Actuator failures and dead-zone constraint exist frequently in practical systems, which will affect the system performance greatly. Based on the improved fuzzy-logic systems (FLSs), a fuzzy adaptive compensation control is established to address these issues. The approximation error is introduced to the control design as a time-varying function. In addition, for the limited transmission resources of the practical system, a two-bit-triggered control mechanism is proposed to further save system transmission resources. It is proved that the proposed method can guarantee the system tracking performance and all the signals are bounded. Its effectiveness is verified by the simulation examples.
TL;DR: A novel piezoelectric inchworms actuator driven by one channel dc signal is developed in this article to simplify excitation signal of the inchworm actuators, and the clamping force of the developed actuator is generated by a dc motor and two permanent magnets.
Abstract: A novel piezoelectric inchworm actuator driven by one channel dc signal is developed in this article to simplify excitation signal of the inchworm actuators, and the clamping force of the developed actuator is generated by a dc motor and two permanent magnets. The piezoelectric stack is excited by a sensing signal, which is generated by the separate photoelectric sensor to detect the position of the rotational permanent magnets. A mathematical model is established to predict the motion of the slider. The prototype of the proposed piezoelectric actuator is fabricated, and mechanical output performance is measured. At a voltage of 75 V and frequency of 3.2 Hz, the average output step is 0.241 μ m under no-load conditions. The proposed inchworm actuator can be operated by just one channel dc signal and the output displacement is stable, which provides a new idea for the integration design of the piezoelectric actuators in the future.
TL;DR: A robust fault tolerant (FT) control scheme for an $n$ -link uncertain robotic system with actuator failures is developed and a nonsingular fast terminal sliding mode is given in order to accelerate the recovery of system stability after failure.
Abstract: This article develops a robust fault tolerant (FT) control scheme for an $n$ -link uncertain robotic system with actuator failures. In order to eliminate the influence of both the uncertainties and actuator failures on the system performance, the Gaussian radial basis function neural networks are used to compensate for the actuator failures and uncertain dynamics. An adaptive observer is designed to compensate for external disturbance. In addition, in order to accelerate the recovery of system stability after failure, a nonsingular fast terminal sliding mode is given. Finally, the simulation results on a two-link manipulator confirms the superior performance of the proposed neural networks-based FT controller, and the experiment results on the Baxter robot further verify the effectiveness of the control method.
TL;DR: A leader-following consensus anti-disturbance and fault-tolerant control (FTC) scheme is proposed for multi-MUAV attitude systems that experience output dead-zone, external disturbance and actuator fault.
Abstract: Many mechanical parts of multi-rotor unmanned aerial vehicle (MUAV) can easily produce non-smooth phenomenon and the external disturbance that affects the stability of MUAV. For multi-MUAV attitude systems that experience output dead-zone, external disturbance and actuator fault, a leader-following consensus anti-disturbance and fault-tolerant control (FTC) scheme is proposed in this paper. In the design process, the effect of unknown nonlinearity in multi-MUAV systems is addressed using neural networks (NNs). In order to balance out the effects of external disturbance and actuator fault, a disturbance observer is designed to compensate for the aforementioned negative impacts. The Nussbaum function is used to address the problem of output dead-zone. The designed fault-tolerant controller guarantees that the output signals of all followers and leader are synchronized by the backstepping technique. Finally, the effectiveness of the control scheme is verified by simulation experiments.
TL;DR: In this article, a smart soft actuator with multiple capabilities of humidity-driven actuating, humidity energy harvesting, self-powered humidity sensing, and real-time motion tracking is reported.
Abstract: A smart soft actuator with multiple capabilities of humidity-driven actuating, humidity energy harvesting, self-powered humidity sensing, and real-time motion tracking is reported. It is designed on the basis of an MXene/cellulose/polystyrene sulfonic acid (PSSA) composite membrane. This actuator is driven by asymmetric expansion under a moisture gradient during capture of the chemical potential of humidity to mechanical power. Meanwhile, the gradient moisture chemistry also induces directional proton diffusion to generate electricity with high power density and open-circuit voltage. A good linear correlation between the humidity sensitivity, electrical signal, and bending state of this actuator allows real-time tracking of motion modes with humidity change without an external power supply. This multifunctional soft actuator can be used for engineering smart switches, artificial fingers, and soft robots with trackable and distinguishable motion patterns, as well as sensitive noncontacting humidity sensor and breathing monitors.
TL;DR: This article exploits balanced model reduction and greedy optimization to efficiently determine sensor and actuator selections that optimize observability and controllability using greedy matrix QR pivoting on the dominant modes of the direct and adjoint balancing transformations.
Abstract: Optimal sensor and actuator selection is a central challenge in high-dimensional estimation and control. Nearly all subsequent control decisions are affected by these sensor and actuator locations. In this work, we exploit balanced model reduction and greedy optimization to efficiently determine sensor and actuator placements that optimize observability and controllability. In particular, we determine locations that optimize scalar measures of observability and controllability via greedy matrix QR pivoting on the dominant modes of the direct and adjoint balancing transformations. Pivoting runtime scales linearly with the state dimension, making this method tractable for high-dimensional systems. The results are demonstrated on the linearized Ginzburg-Landau system, for which our algorithm approximates known optimal placements computed using costly gradient descent methods.
TL;DR: In this paper, a phototunable self-oscillating system with controllable evolution between different modes and loading capability is presented. But the system is limited by the limited number of available oscillation modes due to limited degrees of freedom, inability to control the evolution of different modes, and failure under loading.
Abstract: Self-oscillating systems that enable autonomous, continuous motions driven by an unchanging, constant stimulus would have significant applications in intelligent machines, advanced robotics, and biomedical devices. Despite efforts to gain self-oscillations have been made through artificial systems using responsive soft materials of gels or liquid crystal polymers, these systems are plagued with problems that restrict their practical applicability: few available oscillation modes due to limited degrees of freedom, inability to control the evolution between different modes, and failure under loading. Here we create a phototunable self-oscillating system that possesses a broad range of oscillation modes, controllable evolution between diverse modes, and loading capability. This self-oscillating system is driven by a photoactive self-winding fiber actuator designed and prepared through a twistless strategy inspired by the helix formation of plant-tendrils, which endows the system with high degrees of freedom. It enables not only controllable generation of three basic self-oscillations but also production of diverse complex oscillatory motions. Moreover, it can work continuously over 1270000 cycles without obvious fatigue, exhibiting high robustness. We envision that this system with controllable self-oscillations, loading capability, and mechanical robustness will be useful in autonomous, self-sustained machines and devices with the core feature of photo-mechanical transduction. Self-oscillating systems that enable autonomous motions driven by a constant stimulus find applications in numerous fields but these systems are plagued with problems that restrict their practical applicability. Here, the authors create a photoactive self-winding fiber actuator that possesses a broad range of oscillation modes, controllable evolution between diverse modes, and loading capability.
TL;DR: In this paper, a 2-DOF arched needle insertion device driven by an inertial piezoelectric actuator was proposed, which could perform theoretical unlimited translational movement and full rotation with high step resolution.
Abstract: Insertion into delicate tissue, such as retina vein occlusion, cell manipulation and vitreoretinal injection, poses challenges to surgeons and biomedical researchers due to the high resolution, large movement range, compact structure and multi-DOF output requirements. In order to meet these requirements, a 2-DOF arched needle insertion device driven by inertial piezoelectric actuator was proposed in this work. This device could perform theoretical unlimited translational movement and full rotation with high step resolution. A prototype was fabricated with compact structure, the length and diameter were 230 mm and 32 mm, respectively. The experimental tests were carried out, the insertion device output 2.47 m and 0.56 mrad step distance with maximum velocity of 382 m/s and 200.9 mrad/s under 120 V driving signals, the maximum insertion force of 32 mN was measured. Additionally, a handheld controller with friendly user interface was also developed for open-loop control utilization, which could automatically calculate and generate the required control signals according to the motion command. This device explores the biomedical application of inertial piezoelectric actuator within a compact size, providing a new choice for numerous innovative treatment and biological research involving precision operation.
TL;DR: In this article, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed.
Abstract: Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.
TL;DR: The design and validation of a backdrivable powered knee orthosis for partial assistance of lower-limb musculature is presented, which aims to facilitate daily activities in individuals with musculoskeletal disorders.
Abstract: This paper presents the design and validation of a backdrivable powered knee orthosis for partial assistance of lower-limb musculature, which aims to facilitate daily activities in individuals with musculoskeletal disorders. The actuator design is guided by design principles that prioritize backdrivability, output torque, and compactness. First, we show that increasing the motor diameter while reducing the gear ratio for a fixed output torque ultimately reduces the reflected inertia (and thus backdrive torque). We also identify a tradeoff with actuator torque density that can be addressed by improving the motor's thermal environment, motivating our design of a custom Brushless DC motor with encapsulated windings. Finally, by designing a 7:1 planetary gearset directly into the stator, the actuator has a high package factor that reduces size and weight. Benchtop tests verify that the custom actuator can produce at least 23.9 Nm peak torque and 12.78 Nm continuous torque, yet has less than 2.68 Nm backdrive torque during walking conditions. Able-bodied human subjects experiments (N=3) demonstrate reduced quadriceps activation with bilateral orthosis assistance during lifting-lowering, sit-to-stand, and stair climbing. The minimal transmission also produces negligible acoustic noise.
TL;DR: In this article, a two-dimensional conductive metal-organic framework (MOF) based electrochemical actuator is presented, which consists of vertically oriented and hierarchical Ni-CAT NWAs/CNF electrodes through the use of a facile one-step in situ hydrothermal growth method.
Abstract: Electrically activated soft actuators capable of large deformation are powerful and broadly applicable in multiple fields. However, designing soft actuators that can withstand a high strain, provide a large actuation displacement, and exhibit stable reversibility are still the main challenges toward their practical application. Here, for the first time, we report a two-dimensional (2D) conductive metal-organic framework (MOF) based electrochemical actuator, which consists of vertically oriented and hierarchical Ni-CAT NWAs/CNF electrodes through the use of a facile one-step in situ hydrothermal growth method. The soft actuator prepared in this study demonstrated improvements in actuation performance and benefits from both the intrinsically ordered porous architecture and efficient transfer pathways for fast ion and electron transport; furthermore, this actuator facilitated a considerably high diffusion rate and low interfacial resistance. In particular, the actuator demonstrated a rapid response (<19 s) at a 3 V DC input, large actuation displacement (12.1 mm), and a correspondingly high strain of 0.36% under a square-wave AC voltage of ±3 V. Specifically, the actuator achieved a broad-band frequency response (0.1-20 Hz) and long-term cyclability in air (10000 cycles) with a negligible degradation in actuation performance. Our work demonstrates new opportunities for bioinspired artificial actuators and overcomes current limitations in electrode materials for soft robotics and bionics.