Showing papers on "Actuator published in 2011"

Actuators for Active Flow Control

Abstract: Actuators are transducers that convert an electrical signal to a desired physical quantity. Active flow control actuators modify a flow by providing an electronically controllable disturbance. The field of active flow control has witnessed explosive growth in the variety of actuators, which is a testament to both the importance and challenges associated with actuator design. This review provides a framework for the discussion of actuator specifications, characteristics, selection, design, and classification for aeronautical applications. Actuator fundamentals are discussed, and various popular actuator types used in low-to-moderate speed flows are then described, including fluidic, moving object/surface, and plasma actuators. We attempt to highlight the strengths and inevitable drawbacks of each and highlight potential future research directions.

Decentralized Event-Triggered Control Over Wireless Sensor/Actuator Networks

Abstract: Event-triggered control has been recently proposed as an alternative to the more traditional periodic execution of control tasks. In a typical event-triggered implementation, the control signals are kept constant until the violation of a condition on the state of the plant triggers the recomputation of the control signals. The possibility of reducing the number of recomputations, and thus of transmissions, while guaranteeing desired levels of control performance, makes event-triggered control very appealing in the context of sensor/actuator networks. In particular, by reducing the network traffic we also reduce the energy expenditures of battery powered wireless sensor nodes. In this paper we present a decentralized event-triggered implementation, over sensor/actuator networks, of centralized nonlinear controllers.

Variable Structure Systems With Sliding Modes in Motion Control—A Survey

Abstract: This paper presents a comprehensive overview of the application of Variable Structure Systems (VSSs) with Sliding Mode (SM) methods in motion control systems. Our aim is to give implementable sliding mode design solutions for complex motion systems, actuators and supply converters. This paper provides a frame for further study of sliding mode applications in motion control systems.

Development of a High-Bandwidth XY Nanopositioning Stage for High-Rate Micro-/Nanomanufacturing

Abstract: This paper presents the design analysis fabrication and testing of a high-bandwidth piezo-driven parallel kinematic nanopositioning XY stage. The monolithic stage design has two axes and each axis is composed of a doubly clamped beam and a parallelogram hybrid flexure with compliant beams and circular flexure hinges. The doubly clamped beam that is actuated by a piezoelectric actuator acts as a linear prismatic axis. The parallelogram hybrid flexures are used to decouple the actuation effect from the other axis. The mechanism design decouples the motion in the X- and Y-directions and restricts parasitic rotations in the XY plane while allowing for an increased bandwidth with linear kinematics in the operating region. Kinematic and dynamic analysis shows that the mechanical structure of the stage has decoupled motion in XY-direction while achieving high bandwidth and good linearity. The stage is actuated by piezoelectric stack actuators, and two capacitive gauges were added to the system to build a closed-loop positioning system. The results from frequency tests show that the resonant frequencies of the two vibrational modes are over 8 kHz. The stage is capable of about 15 μm of motion along each axis with a resolution of about 1 nm. Due to parallel kinematic mechanism design, a uniform performance is achieved across the workspace. A PI controller is implemented for the stage and a closed-loop bandwidth of 2 kHz is obtained.

AwAS-II: A new Actuator with Adjustable Stiffness based on the novel principle of adaptable pivot point and variable lever ratio

Abstract: The Actuator with Adjustable Stiffness (AwAS) is an actuator which can independently control equilibrium position and stiffness by two motors. The first motor controls the equilibrium position while the second motor regulates the compliance. This paper describes the design and development of AwAS-II which is an improved version of the original realization. AwAS tuned the stiffness by controlling the location of the springs and adjusting its arm, length. Instead AwAS-II regulates the compliance by implementing a force amplifier based on a lever mechanism on which a pivot point can adjust the force amplification ratio from zero to infinitive. As in the first implementation, the actuator which is responsible for adjusting the stiffness in AwAS II is not working against the spring forces. Its displacement is perpendicular to the force generated by springs which makes changing the stiffness energetically efficient. As the force amplification ratio can theoretically change from zero to infinitive consequently the level of stiffness can tune from very soft to completely rigid. Because this range does not depends on the spring's rate and length of the lever, thus soft springs and small lever can be used which result in a lighter and more compact setup. Furthermore as the lever arm is shorter the time required for the stiffness regulation is smaller.

A new variable stiffness actuator (CompAct-VSA): Design and modelling

Abstract: This paper describes the design and modelling of a new variable stiffness actuator (CompAct-VSA). The principle of operation of CompAct-VSA is based on a lever arm mechanism with a continuously regulated pivot point. The proposed concept allows for the development of an actuation unit with a wide range of stiffness and a fast stiffness regulation response. The implementation of the actuator makes use of a cam shaped lever arm with a variable pivot axis actuated by a rack and pinion transmission system. This realization results in a highly integrated and modular assembly. Size and weight are indeed an open issue in the VSAs design, which ultimately limit their implementation in multi-dof robotic systems. The paper introduces the mechanics, the principle of operation and the model of the actuator. Preliminary results are presented to demonstrate the fast stiffness regulation response and the wide range of stiffness achieved by the proposed CompAct-VSA design.

High-performance, low-voltage, and easy-operable bending actuator based on aligned carbon nanotube/polymer composites.

Abstract: In this work, we show that embedding super-aligned carbon nanotube sheets into a polymer matrix (polydimethylsiloxane) can remarkably reduce the coefficient of thermal expansion of the polymer matrix by two orders of magnitude. Based on this unique phenomenon, we fabricated a new kind of bending actuator through a two-step method. The actuator is easily operable and can generate an exceptionally large bending actuation with controllable motion at very low driving DC voltages (<700 V/m). Furthermore, the actuator can be operated without electrolytes in the air, which is superior to conventional carbon nanotube actuators. Proposed electrothermal mechanism was discussed and confirmed by our experimental results. The exceptional bending actuation performance together with easy fabrication, low-voltage, and controllable motion demonstrates the potential ability of using this kind of actuator in various applicable areas, such as artificial muscles, microrobotics, microsensors, microtransducers, micromanipulatio...

Active Control for an Offshore Crane Using Prediction of the Vessel’s Motion

Abstract: During offshore installations in harsh sea conditions, the involved crane system must satisfy rigorous requirements in terms of safety and efficiency. The forces resulting from the vertical motion of the vessel have an extensive effect on the overall crane structure and its lifetime. Moreover, vessel motion handicaps the operator during fine positioning of the payload. Hence, an active compensation system for the vertical vessel motion is proposed. An important point to consider for such systems is the time delay between the sensors and actuators, which diminishes performance. To compensate the dead times in the system, a prediction algorithm for the vertical motion of the vessel is proposed in the first part. In the second part, an inversion-based control strategy for the hydraulic-driven winch is formulated that considers the dynamic behavior of the drive system. A feedforward controller compensates the vertical-motion disturbance using the predicted motion. The proposed controller together with the prediction algorithm decouple the motion of the rope-suspended payload from the vessel's motion. The active compensation approach is evaluated with simulation and measurement results.

Energy-Efficient Variable Stiffness Actuators

Abstract: Variable stiffness actuators are a particular class of actuators that is characterized by the property that the apparent output stiffness can be changed independent of the output position. To achieve this, variable stiffness actuators consist of a number of elastic elements and a number of actuated degrees of freedom, which determine how the elastic elements are perceived at the actuator output. Changing the apparent output stiffness is useful for a broad range of applications, which explains the increasing research interest in this class of actuators. In this paper, a generic, port-based model for variable stiffness actuators is presented, with which a wide variety of designs can be modeled and analyzed. From the analysis of the model, it is possible to derive kinematic properties that variable stiffness actuator designs should satisfy in order to be energy efficient. More specifically, the kinematics should be such that the apparent output stiffness can be varied without changing the potential energy that is stored in the internal elastic elements. A concept design of an energy-efficient variable stiffness actuator is presented and implemented. Simulations of the model and experiments on the realized prototype validate the design principle.

Fluidic lens with reduced optical aberration

Abstract: A fluidic optical device may include a first optical surface that includes an deformable material and a second optical surface that includes a rigid material. An optical fluid disposed between first and second optical surfaces and an actuator is disposed in communication with first optical surface. Activation of actuator results in a deformation of first optical surface and displacement of optical fluid. The deformation and displacement result in a change in an optical property of the device. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Efficiency of a Regenerative Direct-Drive Electromagnetic Active Suspension

Abstract: The efficiency and power consumption of a direct-drive electromagnetic active suspension system for automotive applications are investigated. A McPherson suspension system is considered, where the strut consists of a direct-drive brushless tubular permanent-magnet actuator in parallel with a passive spring and damper. This suspension system can both deliver active forces and regenerate power due to imposed movements. A linear quadratic regulator controller is developed for the improvement of comfort and handling (dynamic tire load). The power consumption is simulated as a function of the passive damping in the active suspension system. Finally, measurements are performed on a quarter-car test setup to validate the analysis and simulations.

Two-way reversible shape memory effects in a free-standing polymer composite

Abstract: Shape memory polymers (SMPs) have attracted significant research efforts due to their ease in manufacturing and highly tailorable thermomechanical properties. SMPs can be temporarily programmed and fixed in a nonequilibrium shape and are capable of recovering the original undeformed shape upon exposure to a stimulus, the most common being temperature. Most SMPs exhibit a one-way shape memory (1W-SM) effect since one programming step can only yield one shape memory cycle; an additional shape memory cycle requires an extra programming step. Recently, a novel SMP that demonstrates both 1W-SM and two-way shape memory (2W-SM) effects was demonstrated by one of the authors (Mather). However, to achieve two-way actuation this SMP relies on a constant externally applied load. In this paper, an SMP composite where a pre-stretched 2W-SMP is embedded in an elastomeric matrix is developed. This composite demonstrates 2W-SM effects in response to changes in temperature without the requirement of a constant external load. A transversal actuation of ~ 10% of actuator length is achieved. Cyclic tests show that the transversal actuation stabilizes after an initial training cycle and shows no significant decreases after four cycles. A simple analytic model considering the programming stress and actuator dimensions is presented and shown to agree well with the transverse displacement of the actuator. The model also predicts that larger actuation can be achieved when larger pre-stretch of 2W-SMP is used. The scheme used for this polymer composite can promote the design of new shape memory composites at micro- and nano-length scales to meet different application requirements.

VSA-CubeBot: A modular variable stiffness platform for multiple degrees of freedom robots

Abstract: We propose a prototype of a Variable Stiffness Actuator (VSA) conceived with low cost as its first goal. This approach was scarcely covered in past literature. Many recent works introduced a large number of actuators with adjustable stiffness, optimized for a wide set of applications. They cover a broad range of design possibilities, but their availability is still limited to small quantities. This work presents the design and implementation of a modular servo-VSA multi-unit system, called VSA-CubeBot. It offers a customizable platform for the realization and test of variable stiffness robotic structures with many degrees of freedom. We present solutions relative to the variable stiffness mechanism, embedded electronics, mechanical and electrical interconnections. Characteristics, both theoretic and experimental, of the single actuator are reported and, finally, five units are interconnected to form a single arm, to give an example of the many possible applications of this modular VSA actuation unit.

Miniature Pneumatic Curling Rubber Actuator Generating Bidirectional Motion with One Air-Supply Tube

Abstract: Soft actuators driven by pneumatic pressure are promising actuators for mechanical systems in medical, biological, agriculture, welfare fields and so on, because they can ensure high safety for fragile objects from their low mechanical impedance. In this study, a new rubber pneumatic actuator made from silicone rubber was developed. Composed of one chamber and one air-supply tube, it can generate curling motion in two directions by using positive and negative pneumatic pressure. The rubber actuator, for generating bidirectional motion, was designed to achieve an efficient shape by nonlinear finite element method analysis, and was fabricated by a molding and rubber bonding process using excimer light. The fabricated actuator was able to generate curling motion in two directions successfully. The displacement and force characteristics of the actuator were measured by using a motion capture system and a load cell. As an example application of the actuator, a robotic soft hand with three actuators was constru...

Power consumption, discharge capacitance and light emission as measures for thrust production of dielectric barrier discharge plasma actuators

Abstract: A new procedure of determining the time resolved capacitance of a plasma actuator during operation is introduced, representing a simple diagnostic tool that provides insight into the phenomenological behavior of plasma actuators. The procedure is demonstrated by presenting example correlations between consumed electrical energy, size of the plasma region, and the operating voltage. It is shown that the capacitance of a plasma actuator is considerably increased by the presence of the plasma; hence a system that has previously been impedance matched can be considerably de-tuned when varying the operating voltage of the actuator. Such information is fundamental for any attempts to increase the energy efficiency of plasma-actuator systems. A combined analysis of the capacitance, light emission, size of the plasma region, force production, and power consumption is presented.

A novel fabrication of ionic polymer–metal composite membrane actuator capable of 3-dimensional kinematic motions

Abstract: Ionic polymer–metal composites (IPMCs) are one type of wet electroactive polymers that show promising actuating properties in many bio-inspiring underwater robotic applications. In these applications, 3-dimensional kinematic motions are desirable to generate high efficient thrust and maneuverability. However, traditional IPMCs are limited in being only able to generate bending motion. In this paper, a novel synthesis technique is developed to fabricate a hybrid IPMC membrane actuator capable of generating 3-dimensional (3D) kinematic motions. The actuator consists of separated IPMC beams bonded with a soft polydimethylsiloxane (PDMS) membrane. By controlling each individual IPMC beams, we can generate complex 3D motions such as oscillation and undulation. IPMC beams are cut from one sheet of IPMC, which is fabricated through chemically plating platinum electrodes on a Nafion film. A multiple plating process is used to enhance the conductivity of the electrodes, which leads to better actuation performance of IPMC. An assembly based fabrication process is adopted to bond the IPMC actuators with PDMS gel using two CNC-machined molds. Then the PDMS is cured at room temperature to form an actuating membrane. Overall this novel synthesis technique is cost effective and less time-consuming compared to existing strategies. The characterization of the actuating membrane has shown that the maximum twist angle can reach up to 15°, the flapping deflection can reach up to 25% of spanwise length, the tip force can reach up to 0.5 g force, and the power consumption is below 0.5 W. The first application of this novel membrane actuator is in the design of a free-swimming robotic batoid ray. The robot consists of two membranes functioning as artificial pectoral fins. Experimental results show that the robot is capable of free swimming with low power consumption.

On the Feasibility and Suitability of MR Fluid Clutches in Human-Friendly Manipulators

Abstract: An investigation into the suitability of magneto-rheological (MR) clutches in the context of developing feasible actuation solutions for physical human-robot interaction is presented. Contact and collision forces pose great danger to humans, and thus, the primary criteria for actuator development is safety. While the majority of existing solutions make use of mechanical compliance in some form, in this paper, we will approach the problem by considering the use of MR clutches for coupling the motor drive to the joint. The suitability of MR actuators to provide an intrinsically safe actuation platform is investigated by modeling the torque to mass, and torque to inertia ratios, as well as output impedance of the MR clutch. These figures are compared to commercially available servo motors as well as mechanically compliant based human-safe actuator models. The MR clutch is analytically shown to have superior mass and inertia characteristics over servo motors while either matching or surpassing the intrinsic safety characteristics of the modeled compliant actuator. The implementation of MR-clutch-based actuation systems is investigated by examining the distributed active semiactive approach. The proposed approach is discussed in terms of mechanical as well controller complexity and relates the investigation to the feasibility of practical implementations. Performance characteristics are empirically investigated by experimentation with a prototype MR clutch constructed for this purpose. The prototype MR clutch can transmit torque up to 75 Nm and has a bandwidth of 30 Hz. Torque to mass and torque to inertia ratios of the prototype MR clutch are substantially greater than that of comparable servo motors. Conclusions drawn from this investigation indicate that indeed MR clutch actuation approaches can be developed to balance safety and performance while maintaining reasonable system complexity.

Robust fault-tolerant control for spacecraft attitude stabilisation subject to input saturation

Abstract: This study investigates the robust fault-tolerant attitude control of an orbiting spacecraft with a combination of unknown actuator failure, input saturation and external disturbances. A fault-tolerant control scheme based on variable structure control is developed that is robust to the partial loss of actuator effectiveness, where the actuators experience a reduced actuation but are still active. The results are then extended to the case in which some of the actuators fail completely, although some redundancy in actuation is assumed. In contrast to traditional fault-tolerant control methods, the proposed controller does not require knowledge of the actuator faults and is implemented without explicit fault detection, separation and accommodation processes. Moreover, the designed controller rigorously enforces actuator saturation constraints. The associated stability proof is constructive and develops a candidate Lyapunov function that shows the attitude and the angular velocities converge asymptotically to zero. Simulation studies are used to evaluate the closed-loop performance of the proposed control solution and illustrate its robustness to external disturbances, unknown actuator faults and even input saturation.

Data-Based Fault-Tolerant Control of High-Speed Trains With Traction/Braking Notch Nonlinearities and Actuator Failures

Abstract: This paper investigates the position and velocity tracking control problem of high-speed trains with multiple vehicles connected through couplers. A dynamic model reflecting nonlinear and elastic impacts between adjacent vehicles as well as traction/braking nonlinearities and actuation faults is derived. Neuroadaptive fault-tolerant control algorithms are developed to account for various factors such as input nonlinearities, actuator failures, and uncertain impacts of in-train forces in the system simultaneously. The resultant control scheme is essentially independent of system model and is primarily data-driven because with the appropriate input-output data, the proposed control algorithms are capable of automatically generating the intermediate control parameters, neuro-weights, and the compensation signals, literally producing the traction/braking force based upon input and response data only- the whole process does not require precise information on system model or system parameter, nor human intervention. The effectiveness of the proposed approach is also confirmed through numerical simulations.

MACCEPA 2.0: compliant actuator used for energy efficient hopping robot Chobino1D

Abstract: The MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) is an electric actuator of which the compliance and equilibrium position are fully independently controllable and both are set by two dedicated servomotor. In this paper an improvement of the actuator is proposed where the torque-angle curve and consequently the stiffness-angle curve can be modified by choosing an appropriate shape of a profile disk, which replaces the lever arm of the original design. The actuator has a large joint angle, torque and stiffness range and these properties can be made beneficial for safe human robot interaction and the construction of energy efficient walking, hopping and running robots. The benefit of the ability to store and release energy is shown by the 1DOF hopping robot Chobino1D. The achieved hopping height is much higher compared to a configuration in which the same motor is used without a series elastic element. The stiffness of the actuator increases with deflection, more closely resembling the properties shown by elastic tissue in humans.

Bi-bellows: Pneumatic bending actuator

Abstract: We present a compliant single degree-of-freedom pneumatic actuator with large bending capabilities. Several actuator designs are compared and validated against the suggested actuation model. Repeatability, some dynamic properties and the affect of external loads are examined as well.

Linear-Quadratic Optimal Actuator Location

Abstract: In control of vibrations, diffusion and many other problems governed by partial differential equations, there is freedom in the choice of actuator location. The actuator location should be chosen to optimize performance objectives. In this paper, we consider linear quadratic performance. Two types of cost are considered; the choice depends on whether the response to the worst initial condition is to be minimized; or whether the initial condition is regarded as random. In practice, approximations are used in controller design and thus in selection of the actuator locations. The optimal cost and location of the approximating sequence should converge to the exact optimal cost and location. In this work conditions for this convergence are given in the case of linear quadratic control. Examples are provided to illustrate that convergence may fail when these conditions are not satisfied.

Modeling of Piezoelectric-Driven Stick–Slip Actuators

Abstract: Piezoelectric-driven stick-slip actuators have been drawing extensive attention in various applications of long-range and ultraprecision positioning. In such an actuator, the dynamics of the end-effector displacement is of importance for its design and control, yet challenging to be modeled due to the complexity involved. By taking into account the linear dynamics and hysteretic behavior of the piezoelectric actuator (PEA), as well as the presliding friction on the end-effector, a model representative of the end-effector displacement is presented in this paper. The effectiveness of the developed model is illustrated by the experiments on the piezoelectric-driven stick-slip actuator prototyped in the authors' laboratory.

Fault Diagnosis and Fault-Tolerant Control Strategy for the Aerosonde UAV

Abstract: A fault detection and diagnosis (FDD) and a fault-tolerant control (FTC) system for an unmanned aerial vehicle (UAV) subject to control surface failures are presented. This FDD/FTC technique is designed considering the following constraints: the control surface positions are not measured and some actuator faults are not isolable. Moreover, the aircraft has an unstable spiral mode and offers few actuator redundancies. Thus, to compensate for actuator faults, the healthy controls may move close to their saturation values and the aircraft may become uncontrollable; this is critical due to its open-loop unstability. A nonlinear aircraft model designed for FTC researches has been proposed. It describes the aerodynamic effects produced by each control surface. The diagnosis system is designed with a bank of unknown input decoupled functional observers (UIDFO) which is able to estimate unknown inputs. It is coupled with an active diagnosis method in order to isolate the faulty control. Once the fault is diagnosed, an FTC based on state feedback controllers aims at sizing the stability domain with respect to the flight envelope and actuator saturations while setting the dynamics of the closed-loop system. The complete system was demonstrated in simulation with a nonlinear model of the aircraft.

Limitations of Linear Control Over Packet Drop Networks

Abstract: In this paper, we investigate control across stochastic dropout channels. In particular, we consider the Mean Square Stability of a SISO plant in the case there is only one channel in the feedback loop and the case where both actuator and sensor channels are present. We seek optimal networked control schemes that are memoryless functions of channel state information and for each channel state are otherwise linear and time invariant functions of channel output. We establish a fundamental limit on the dropout probability allowable for the Mean Square Stability of the closed loop system. The maximal tolerable dropout probability is only a function of the unstable eigenvalues of the plant. When either the actuator or the sensor channel is present, we propose a receiver structure that can stabilize the system under the worst dropout probability; moreover, we can simultaneously design the optimal controller and receiver and show that they can be implemented in physically separated locations (decentralized). When both actuator and sensor channels are present in the loop, the main result is a centralized stabilization technique that always achieves the fundamental bound via noiseless acknowledgement from the actuation receiver. Finally, we extend the results to the more general case where also the acknowledgements are lost with a given probability and compute how the unreliable delivery of the acknowledgements affects the minimal quality of service required of the actuator and sensor channels.

Fault-tolerant sliding mode attitude control for flexible spacecraft under loss of actuator effectiveness

Abstract: In this paper, a novel fault-tolerant attitude control synthesis is carried out for a flexible spacecraft subject to actuator faults and uncertain inertia parameters. Based on the sliding mode control, a fault-tolerant control law for the attitude stabilization is first derived to protect against the partial loss of actuator effectiveness. Then the result is extended to address the problem that the actual output of the actuators is constrained. It is shown that the presented controller can accommodate the actuator faults, even while rejecting external disturbances. Moreover, the developed control law can rigorously enforce actuator-magnitude constraints. An additional advantage of the proposed fault-tolerant control strategy is that the control design does not require a fault detection and isolation mechanism to detect, separate, and identify the actuator faults on-line; the knowledge of certain bounds on the effectiveness factors of the actuator is not used via the adaptive estimate method. The associated stability proof is constructive and accomplished by the development of the Lyapunov function candidate, which shows that the attitude orientation and angular velocity will globally asymptotically converge to zero. Numerical simulation results are also presented which not only highlight the ensured closed-loop performance benefits from the control law derived here, but also illustrate its superior fault tolerance and robustness in the face of external disturbances when compared with the conventional approaches for spacecraft attitude stabilization control.