Showing papers on "Actuator published in 2016"

Survey on Recent Advances in Networked Control Systems

Abstract: Networked control systems (NCSs) are systems whose control loops are closed through communication networks such that both control signals and feedback signals can be exchanged among system components (sensors, controllers, actuators, and so on). NCSs have a broad range of applications in areas such as industrial control and signal processing. This survey provides an overview on the theoretical development of NCSs. In-depth analysis and discussion is made on sampled-data control, networked control, and event-triggered control. More specifically, existing research methods on NCSs are summarized. Furthermore, as an active research topic, network-based filtering is reviewed briefly. Finally, some challenging problems are presented to direct the future research.

Fixed-Time Attitude Control for Rigid Spacecraft With Actuator Saturation and Faults

Abstract: This brief investigates the finite-time control problem associated with attitude stabilization of a rigid spacecraft subject to external disturbance, actuator faults, and input saturation. More specifically, a novel fixed-time sliding mode surface is developed, and the settling time of the defined surface is shown to be independent of the initial conditions of the system. Then, a finite-time controller is derived to guarantee that the closed-loop system is stable in the sense of the fixed-time concept. The actuator-magnitude constraints are rigorously enforced and the attitude of the rigid spacecraft converges to the equilibrium in a finite time even in the presence of external disturbances and actuator faults. Numerical simulations illustrate the spacecraft performance obtained using the proposed controller.

Adaptive Neural Fault-Tolerant Control of a 3-DOF Model Helicopter System

Abstract: In this paper, an adaptive neural fault-tolerant control scheme is proposed for the three degrees of freedom model helicopter, subject to system uncertainties, unknown external disturbances, and actuator faults. To tackle system uncertainty and nonlinear actuator faults, a neural network disturbance observer is developed based on the radial basis function neural network. The unknown external disturbance and the unknown neural network approximation errors are treated as a compound disturbance that is estimated by another nonlinear disturbance observer. A disturbance observer-based adaptive neural fault-tolerant control scheme is then developed to track the desired system output in the presence of system uncertainty, external disturbance, and actuator faults. The stability of the whole closed-loop system is analyzed using the Lyapunov method, which guarantees the convergence of all closed-loop signals. Finally, the simulation results are presented to illustrate the effectiveness of the new control design techniques.

Minimal Actuator Placement With Bounds on Control Effort

Abstract: We address the problem of minimal actuator placement in a linear system subject to an average control energy bound. First, following the recent work of Olshevsky, we prove that this is NP-hard. Then, we provide an efficient algorithm which, for a given range of problem parameters, approximates up to a multiplicative factor of $O(\log n)$ , with $n$ being the network size, any optimal actuator set that meets the same energy criteria; this is the best approximation factor one can achieve in polynomial time in the worst case. Moreover, the algorithm uses a perturbed version of the involved control energy metric, which we prove to be supermodular. Next, we focus on the related problem of cardinality-constrained actuator placement for minimum control effort, where the optimal actuator set is selected so that an average input energy metric is minimized. While this is also an NP-hard problem, we use our proposed algorithm to efficiently approximate its solutions as well. Finally, we run our algorithms over large random networks to illustrate their efficiency.

Output-Feedback Based Sliding Mode Control for Fuzzy Systems With Actuator Saturation

Abstract: In this paper, a novel adaptive sliding mode controller is designed for Takagi–Sugeno (T–S) fuzzy systems with actuator saturation and system uncertainty. By the delta operator approach, the discrete-time nonlinear system is described by a T–S fuzzy model with unmeasurable state. By singular value decomposition of system input matrix, a reduced-order system is obtained for the design of sliding mode surface. A new adaptive sliding mode controller based on system output is presented to guarantee that the closed-loop system is uniformly ultimately bounded. Four examples are provided to illustrate the effectiveness and applicability of the proposed control scheme.

A Soft Jellyfish Robot Driven by a Dielectric Elastomer Actuator

Abstract: Although dielectric elastomers have been extensively studied recently, to date there has been little research into application of dielectric elastomer actuators to undersea robots. This letter focuses on development of a jellyfish robot using a dielectric elastomer actuator, which exhibits muscle-like properties including large deformation and high energy density. We carry out experiments to test the actuator’s deformation and force. Theoretical simulations are conducted to analyze the performance of the actuator, which are qualitatively consistent with the experiments. The preliminary studies show that this jellyfish robot based on dielectric elastomer technology can move effectively in water. The robot also exhibits fast response and high capacity of payload (compared to its self-weight).

A Soft Modular Manipulator for Minimally Invasive Surgery: Design and Characterization of a Single Module

Abstract: This paper presents the concept design of a modular soft manipulator for minimally invasive surgery. Unlike traditional surgical manipulators based on metallic steerable needles, tendon-driven mechanisms, or articulated motorized links, we combine flexible fluidic actuators to obtain multidirectional bending and elongation with a variable stiffness mechanism based on granular jamming. The idea is to develop a manipulator based on a series of modules, each consisting of a silicone matrix with pneumatic chambers for 3-D motion, and one central channel for the integration of granular-jamming-based stiffening mechanism. A bellows-shaped braided structure is used to contain the lateral expansion of the flexible fluidic actuator and to increase its motion range. In this paper, the design and experimental characterization of a single module composed of such a manipulator is presented. Possible applications of the manipulator in the surgical field are discussed.

Flexible and Stretchable Strain Sensing Actuator for Wearable Soft Robotic Applications

Abstract: Despite the emergence of flexible and stretchable actuators, few possess sensing capabilities. Here, we present a facile method of integrating a flexible pneumatic actuator with stretchable strain sensor to form a soft sensorized actuator. The elastomeric actuator comprises a microchannel connected to a controlled air source to achieve bending. The strain sensor comprises a thin layer of screen-printed silver nanoparticles on an elastomeric substrate to achieve its stretchability and flexibility while maintaining excellent conductivity at ≈8 Ω sq–1. By printing a mesh network of conductive structures, our strain sensor is able to detect deformations beyond 20% with a high gauge factor beyond 50 000. The integration of a pneumatic soft actuator with our sensing element enables the measurement of the extent of actuator bending. To demonstrate its potential as a rehabilitation sensing actuator, we fit the sensorized actuator in a glove to further analyze finger kinematics. With this, we are able to detect irregular movement patterns in real time and assess finger stiffness or dexterity.

Self-expanding/shrinking structures by 4D printing

Abstract: The aim of this paper is to create adaptive structures capable of self-expanding and self-shrinking by means of four-dimensional printing technology. An actuator unit is designed and fabricated directly by printing fibers of shape memory polymers (SMPs) in flexible beams with different arrangements. Experiments are conducted to determine thermo-mechanical material properties of the fabricated part revealing that the printing process introduced a strong anisotropy into the printed parts. The feasibility of the actuator unit with self-expanding and self-shrinking features is demonstrated experimentally. A phenomenological constitutive model together with analytical closed-form solutions are developed to replicate thermo-mechanical behaviors of SMPs. Governing equations of equilibrium are developed for printed structures based on the non-linear Green–Lagrange strain tensor and solved implementing a finite element method along with an iterative incremental Newton–Raphson scheme. The material-structural model is then applied to digitally design and print SMP adaptive lattices in planar and tubular shapes comprising a periodic arrangement of SMP actuator units that expand and then recover their original shape automatically. Numerical and experimental results reveal that the proposed planar lattice as meta-materials can be employed for plane actuators with self-expanding/shrinking features or as structural switches providing two different dynamic characteristics. It is also shown that the proposed tubular lattice with a self-expanding/shrinking mechanism can serve as tubular stents and grippers for bio-medical or piping applications.

Approximate Back-Stepping Fault-Tolerant Control of the Flexible Air-Breathing Hypersonic Vehicle

Abstract: This paper deals with fault-tolerant output tracking control for the flexible air-breathing hypersonic vehicle (AHV) subject to parametric uncertainties, external disturbances, and actuator constraints. By regarding the flexible dynamics as equivalent disturbances, the vehicle model can be split into three functional subsystems, namely, horizontal translation subsystem, vertical translation subsystem, and rotation subsystem. Then, for each subsystem, a disturbance observer is utilized to estimate the lumped effect of model uncertainties, external disturbances, and actuator faults, while a novel auxiliary system combined with the command prefilter is constructed to handle the physical constraints on actuators. Furthermore, sliding mode control is employed to design control commands for the three subsystems, sequentially. The proposed controller modifies the reference trajectories dynamically when one or more actuators become constrained, and can steer the AHV to the desired trim finally. Simulation results are provided to demonstrate the effectiveness of the designed controller.

Design and Analysis of a Soft Pneumatic Actuator with Origami Shell Reinforcement

Abstract: Soft pneumatic actuators (SPAs) are versatile robotic components enabling diverse and complex soft robot hardware design. However, due to inherent material characteristics exhibited by their primary constitutive material, silicone rubber, they often lack robustness and repeatability in performance. In this article, we present a novel SPA-based bending module design with shell reinforcement. The bidirectional soft actuator presented here is enveloped in a Yoshimura patterned origami shell, which acts as an additional protection layer covering the SPA while providing specific bending resilience throughout the actuator's range of motion. Mechanical tests are performed to characterize several shell folding patterns and their effect on the actuator performance. Details on design decisions and experimental results using the SPA with origami shell modules and performance analysis are presented; the performance of the bending module is significantly enhanced when reinforcement is provided by the shell. W...

Stretchable Materials for Robust Soft Actuators towards Assistive Wearable Devices.

Abstract: Soft actuators made from elastomeric active materials can find widespread potential implementation in a variety of applications ranging from assistive wearable technologies targeted at biomedical rehabilitation or assistance with activities of daily living, bioinspired and biomimetic systems, to gripping and manipulating fragile objects, and adaptable locomotion. In this manuscript, we propose a novel two-component soft actuator design and design tool that produces actuators targeted towards these applications with enhanced mechanical performance and manufacturability. Our numerical models developed using the finite element method can predict the actuator behavior at large mechanical strains to allow efficient design iterations for system optimization. Based on two distinctive actuator prototypes’ (linear and bending actuators) experimental results that include free displacement and blocked-forces, we have validated the efficacy of the numerical models. The presented extensive investigation of mechanical performance for soft actuators with varying geometric parameters demonstrates the practical application of the design tool, and the robustness of the actuator hardware design, towards diverse soft robotic systems for a wide set of assistive wearable technologies, including replicating the motion of several parts of the human body.

Velocity-Free Fault-Tolerant and Uncertainty Attenuation Control for a Class of Nonlinear Systems

Abstract: This paper addresses a difficult problem of velocity-free uncertain attenuation control for a class of nonlinear systems with external disturbance and multiple actuator faults. With only the output measurement available for feedback, a sliding-mode observer (SMO) is proposed to reconstruct the full states. The reconstructed signal can approximate the true value to any accuracy. An adaptive version of the observer is further presented to handle a class of structured uncertainties in the system. Together with the system output feedback, the reconstructed state is used to synthesize a velocity-free controller. All states in the closed-loop system are guaranteed to be uniformly ultimately bounded (UUB). System uncertainty and external disturbances are attenuated. Actuator fault is accommodated. An example with application the approach to satellite attitude stabilization maneuver is presented to verify the effectiveness of the proposed scheme.

Multiresponsive Bidirectional Bending Actuators Fabricated by a Pencil-on-Paper Method

Abstract: Recently, actuating materials based on carbon nanotubes or graphene have been widely studied. However, present carbon-based actuating materials are mostly driven by a single stimulus (humidity, light, electricity, etc.), respectively, which means that the application conditions are limited. Here, a new kind of multiresponsive actuating material which can be driven by humidity, light, and electricity is proposed, so it can be used in various conditions. The fabrication is based on the simplest pencil-on-paper method, in which the pencil and paper are both low-cost and easily obtained daily materials. The actuation effect is more remarkable due to a dual-mode actuation mechanism, which leads to an ultralarge actuation (bending curvature up to 2.6 cm−1). Elaborately designed, the actuator can further exhibit a bidirectional bending actuation, which is a significant improvement compared with previous reported thermal actuators. What is more, a colorful biomimetic flower and a smart curtain are also fabricated, fully utilizing the printable characteristic of the paper and multiresponsive characteristic of the actuator. It is assumed that the newly designed actuating material has great potential in the fields of lab-on-paper devices, artificial muscles, robotics, biomimics, and smart household materials.

Gravity compensation in robotics

Abstract: The actuator power required to resist joint torque caused by the weight of robot links can be a significant problem. Gravity compensation is a well-known technique in robot design to achieve equilibrium throughout the range of motion and as a result to reduce the loads on the actuator. Therefore, it is desirable and commonly implemented in many situations. Various design concepts for gravity compensation are available in the literature. This paper proposes an overview of gravity compensation methods applied in robotics. The examined properties of the gravity compensation are disclosed and illustrated via kinematic schemes. In order to classify the considered balancing schemes three principal groups are distinguished due to the nature of the compensation force: counterweight, spring or active force developed by an auxiliary actuator. Then, each group is reviewed through sub-groups organized via structural features of balancing schemes. The author believes that such an arrangement of gravity compensation me...

Giving Direction to Motion and Surface with Ultra‐Fast Speed Using Oriented Hydrogel Fibers

Abstract: Thermoresponsive hydrogel fibrous membranes showing directionally controlled movements and surface change with ultra-fast speed are presented for the first time. They show reversible coiling, rolling, bending, and twisting deformations in different controllable directions for many cycles (at least 50 cycles tried) with inside-out change in surfaces and shapes. Speed, reversibility, large-scale deformations and, most importantly, control over the direction of deformation is required in order to make synthetic actuators inspired from natural materials or otherwise. A polymeric synthetic material combining all these properties is still awaited. This issue is addressed and provide a very simple system fulfilling all these requirements by combining porosity and asymmetric swelling/shrinking via orientation of hydrogel fibers at different angles in a fibrous membrane. Electrospinning is used as a tool for making membranes with fibers oriented at different angles.

One-volt-driven superfast polymer actuators based on single-ion conductors.

Abstract: The key challenges in the advancement of actuator technologies related to artificial muscles include fast-response time, low operation voltages and durability. Although several researchers have tackled these challenges over the last few decades, no breakthrough has been made. Here we describe a platform for the development of soft actuators that moves a few millimetres under 1 V in air, with a superfast response time of tens of milliseconds. An essential component of this actuator is the single-ion-conducting polymers that contain well-defined ionic domains through the introduction of zwitterions; this achieved an exceptionally high dielectric constant of 76 and a 300-fold enhancement in ionic conductivity. Moreover, the actuator demonstrated long-term durability, with negligible changes in the actuator stroke over 20,000 cycles in air. Owing to its low-power consumption (only 4 mW), we believe that this actuator could pave the way for cutting-edge biomimetic technologies in the future. Achieving a balance of desirable mechanical properties with low power consumption is important for developing soft actuator technologies. Here, the authors report single-ion-conducting polymers that function as fast, durable actuators at low voltages.

An Acceleration-Based Robust Motion Controller Design for a Novel Series Elastic Actuator

Abstract: This paper proposes an acceleration-based robust controller for the motion control problem, i.e., position and force control problems, of a novel series elastic actuator (SEA). A variable stiffness SEA is designed by using soft and hard springs in series so as to relax the fundamental performance limitation of conventional SEAs. Although the proposed SEA intrinsically has several superiorities in force control, its motion control problem, especially position control problem, is harder than conventional stiff and SEAs due to its special mechanical structure. It is shown that the performance of the novel SEA is limited when conventional motion control methods are used. The performance of the steady-state response is significantly improved by using disturbance observer (DOb), i.e., improving the robustness; however, it degrades the transient response by increasing the vibration at tip point. The vibration of the novel SEA and external disturbances are suppressed by using resonance ratio control (RRC) and arm DOb, respectively. The proposed method can be used in the motion control problem of conventional SEAs as well. The intrinsically safe mechanical structure and high-performance motion control system provide several benefits in industrial applications, e.g., robots can perform dexterous and versatile industrial tasks alongside people in a factory setting. The experimental results show viability of the proposals.

Construction of a Fish-like Robot Based on High Performance Graphene/PVDF Bimorph Actuation Materials.

Abstract: Smart actuators have many potential applications in various areas, so the development of novel actuation materials, with facile fabricating methods and excellent performances, are still urgent needs. In this work, a novel electromechanical bimorph actuator constituted by a graphene layer and a PVDF layer, is fabricated through a simple yet versatile solution approach. The bimorph actuator can deflect toward the graphene side under electrical stimulus, due to the differences in coefficient of thermal expansion between the two layers and the converse piezoelectric effect and electrostrictive property of the PVDF layer. Under low voltage stimulus, the actuator (length: 20 mm, width: 3 mm) can generate large actuation motion with a maximum deflection of about 14.0 mm within 0.262 s and produce high actuation stress (more than 312.7 MPa/g). The bimorph actuator also can display reversible swing behavior with long cycle life under high frequencies. on this basis, a fish-like robot that can swim at the speed of 5.02 mm/s is designed and demonstrated. The designed graphene-PVDF bimorph actuator exhibits the overall novel performance compared with many other electromechanical avtuators, and may contribute to the practical actuation applications of graphene-based materials at a macro scale.

Adaptive Control for Teleoperation System With Varying Time Delays and Input Saturation Constraints

Abstract: This paper addresses the adaptive control of teleoperation system with actuator saturation. To unify the study of actuator saturation, passive/nonpassive external forces, asymmetric time-varying delays, and unknown dynamics in the same framework, a novel switched control scheme is developed, where a special switched filter is investigated. In the saturation scenario, the designed controller consists of a generalized controller and a nonlinear saturation function. By placing the nonlinear saturation function on the outside of the generalized controller, and further jointing with the design of switched filter, the designed generalized controller needs not consider the actuator saturation. Specifically, it is designed to be in the form of proportional plus damping injection plus switched filter. Then, the complete closed-loop system is modeled as a special switched system. It is finally established to be state-independent input-to-output stable, where the ultimate boundedness of the tracking error is ensured for any bounded exogenous forces, which is demonstrated by the experimental studies.

35 Hz shape memory alloy actuator with bending-twisting mode.

Abstract: Shape Memory Alloy (SMA) materials are widely used as an actuating source for bending actuators due to their high power density. However, due to the slow actuation speed of SMAs, there are limitations in their range of possible applications. This paper proposes a smart soft composite (SSC) actuator capable of fast bending actuation with large deformations. To increase the actuation speed of SMA actuator, multiple thin SMA wires are used to increase the heat dissipation for faster cooling. The actuation characteristics of the actuator at different frequencies are measured with different actuator lengths and results show that resonance can be used to realize large deformations up to 35 Hz. The actuation characteristics of the actuator can be modified by changing the design of the layered reinforcement structure embedded in the actuator, thus the natural frequency and length of an actuator can be optimized for a specific actuation speed. A model is used to compare with the experimental results of actuators with different layered reinforcement structure designs. Also, a bend-twist coupled motion using an anisotropic layered reinforcement structure at a speed of 10 Hz is also realized. By increasing their range of actuation characteristics, the proposed actuator extends the range of application of SMA bending actuators.

Active Fault-Tolerant Control for Electric Vehicles With Independently Driven Rear In-Wheel Motors Against Certain Actuator Faults

Abstract: An active fault-tolerant control (AFTC) system is proposed in this paper for electric vehicles with independently driven in-wheel motors (IWMs). It comprises a baseline controller, a set of reconfigurable controllers, a fault detection and diagnosis (FDD) mechanism, and a decision mechanism. The baseline controller, which is actually a passive fault-tolerant controller, is applied to accommodate actuator faults and stabilize the faulty vehicle when the actuator fault occurs. After the fault is detected and estimated by the FDD mechanism, a proper reconfigurable controller is switched ON to achieve optimal postfault performance. Taking advantage of the robust gain-scheduling algorithm, the loss-of-effectiveness and additive faults of the IWMs can be accommodated by the baseline controller, and the estimation error of the FDD mechanism can be tolerated by the reconfigurable controllers. The results of simulations in CarSim and vehicle experimental tests show the effectiveness of this AFTC system in dealing with certain IWM faults.

A Bonded-Type Piezoelectric Actuator Using the First and Second Bending Vibration Modes

Abstract: A piezoelectric actuator, which is constructed by bonding six pieces of lead zirconate titanate (PZT) ceramic plates on a step aluminum alloy beam, was proposed and tested for the design of a small-size rotary driving appratus. Two pieces of PZT ceramic plates bonded in the middle part is used to generate the first bending mode, whereas the other four on the two sides are set for the excitation of the second bending mode; their superimposition can produce elliptical movements on the two ends of the beam, which can rotate a disk-shaped rotor. Compared with the traditional ring-shaped traveling-wave piezoelectric actuator, the proposed actuator has a simpler structure and operating principle; it also gives a new mode for rotary driving. The resonance frequencies of the first and second bending modes were designed to be close at about 21.1 kHz. The maximum no-load speed and torque were tested to be 158 r/min and 0.053 $\mbox{N}\cdot\mbox{m}$ , respectively. The prototype achieved a power density of 19.0 W/kg under a weight of 15.8 g. The proposed combination plan of the first and second bending modes is very suitable for constructing a small-size piezoelectric actuator, which exhibits merits for application in small systems.

Actuator fault-tolerant control of ocean surface vessels with input saturation

Abstract: Summary In this paper, an actuator robust fault-tolerant control is proposed for ocean surface vessels with parametric uncertainties and unknown disturbances. Using the backstepping technique and Lyapunov synthesis method, the adaptive tracking control is first developed by incorporating the actuator configuration matrix and considering actuator saturation constraints. The changeable actuator configuration matrix caused by rotatable propulsion devices is considered. Next, the actuator fault-tolerant control is developed for the case when faults occur in propulsion devices of the ocean surface vessel. Rigorous stability analysis is carried out to show that the proposed fault-tolerant control can guarantee the stability of the closed-loop system under certain actuator failure. Finally, simulation studies are given to illustrate the effectiveness of the proposed adaptive tracking control and fault-tolerant control. Copyright © 2015 John Wiley & Sons, Ltd.

A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation

Abstract: Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors' knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

Soft morphing hand driven by SMA tendon wire

Abstract: Most existing approaches to developing robotic manipulators or artificial hands have used rigid components, with joints, linkages, gears, and motors. Rigid robotic systems can perform tasks with precise and articulated motion, but require complex integrated feedback-based control systems. Soft robotics is an emerging research field that uses deformable materials to build systems that are compliant and adaptable via simple integrated mechanisms, enabling biomimetic behavior with compact systems. Here, we report a novel tendon-driven bending actuator using smart soft composite (SSC) and shape memory alloy (SMA). First, an artificial finger was designed based on a SMA wire and a sliding mechanism, which mimics flexion of the human hand. This artificial finger has a soft hinge structure to enable the bending motion of the actuator. Experiments were conducted to evaluate the bending and load resistance of the artificial finger, and an optimal material composition was identified. The bending performance of the actuator was measured with various numbers of glass fiber sheets, and two-layered actuator showed the best performance in terms of the trade-off relationship between the bending capacity and the load holding capacity – bending angle of 305° with weight of 20 g and bending angle of 61° with weight of 60 g. Finally, a prototype robotic hand was then developed using four tendon-driven SSC fingers and a thumb, and grasping capabilities were demonstrated with various objects with diverse shapes.