Primary Actuator Research Articles

Electromagnetic synergetic actuators based on polypyrrole/Fe3O4 hybrid nanotube arrays

Conducting polymer actuators that can undergo complex and coordinated motions are generally obtained by using complex microfabrication methods to pattern several conducting polymer components. Herein, we describe a facile approach for fabricating electromagnetic synergetic actuators based on polypyrrole/Fe3O4 hybrid nanotube arrays. The actuator can perform biomimetic movements like arm-hand coordination. In this case, a magnetic field is used for primary actuation like an arm, i.e., large-scale angular movement, and an electric potential is used for secondary adjustment like a hand, i.e., small-scale angular movement.

Dual-Stage Actuator Control Design Using a Doubly Coprime Factorization Approach

This paper first reveals that the tracking and disturbance rejection problems can be decoupled into two independent optimization problems under the 2-DOF control framework. This result is then used for the design of a 2-DOF controller for a dual-stage actuator (DSA) system to provide desired performance of disturbance rejection and step tracking. The 2-DOF controller is designed based on the doubly coprime factorization approach, with which the closed-loop transfer function is expressed explicitly in terms of design parameters. This greatly simplifies the optimization of design parameters in meeting desired specifications. We further study how to use the design parameters to deal with specific problems in the DSA, i.e., control allocation and trajectory planning. For step tracking beyond the secondary actuator range, a nonlinear controller is also used for the primary actuator to complete the task. Experimental results demonstrate the practical implementation of the DSA control system and verify its effectiveness for step tracking and disturbance rejection and its robust performance under load changes.

Dual-Stage HDD Disturbance Cancellation based on an Efficient Adaptive Feedforward Compensation Algorithm

This paper applies an efficient adaptive feedforward compensation (AFC) algorithm for periodic disturbance cancellation on a hard disk drive (HDD) servo system. Such an algorithm is shown to be equivalent to a linear time invariant (LTI) model. With the help of this equivalence, we can easily choose optimal phase advance parameters, precisely predict the upper bounds of the allowable adaptation gains and determine the appropriate coefficients of a feedthrough term. Additionally, in order to obtain higher servo bandwidth, a dual-stage actuated structure is put forward. This dual-stage actuator system consists of a Voice Coil Motor (VCM) as a primary actuator and a micro actuator as a secondary actuator. Such a configuration can further reject the disturbance and maximize the servo system performance. The simulation results in time domain and frequency domain show that this scheme is capable of achieving a satisfactory performance in dealing with disturbances.

Dual-Stage HDD Disturbance Cancellation Based on an Efficient Adaptive Feedforward Compensation Algorithm

This paper applies an efficient adaptive feedforward compensation (AFC) algorithm for periodic disturbance cancellation on hard disk drive (HDD) servo systems. Such an algorithm is shown to be equivalent to a linear time invariant (LTI) model. With the help of this equivalence, we can easily choose optimal phase advance parameters, precisely predict the upper bounds of the allowable adaptation gains and determine the appropriate coefficients of a feedthrough term. Additionally, in order to obtain higher servo bandwidth, dual-stage actuated structure is put forward. This dual-stage actuator system consists of Voice Coil Motor (VCM) as a primary actuator and micro-actuator as a secondary actuator. Such a configuration can further reject the disturbance and maximize the servo system performance. The simulation results in time domain and frequency domain that this scheme is capable of achieving a satisfactory performance in dealing with disturbances.

Romantic "Ghoststory": Lingering Shades of Shelley in <i>Ulysses</i>

Romantic "Ghoststory":Lingering Shades of Shelley in Ulysses Michael Schandorf In A Portrait of the Artist as a Young Man, the influence of the Romantic poets on the developing character of Stephen Dedalus is obvious and acknowledged in, for example, Stephen's defense of Byron. Shelley, however, was a more subtle, but arguably more lasting Romantic influence on the stylistic and aesthetic development of both Stephen Dedalus and Joyce himself. Nevertheless, most critics seem to have generally ignored or brushed off Shelley's influence in Ulysses as either an inconsequential youthful hold-over or as mere scaffolding on which Stephen's (and Joyce's) more mature aesthetic thought was erected. While the number of influences that bear on Ulysses is truly astounding, the absence of any detailed exploration of Shelley's influence is curious considering the importance of the Defence of Poetry's articulation of the ideal role of poetry and the poet, grounded in Shelley's belief in the power of universal love. Furthermore, an analysis of Shelley's Alastor; or, The Spirit of Solitude reveals several interesting correlations between the Shelleyan poet and both Stephen Dedalus and Bloom, who after all has "a touch of the artist" in him. The Romantic poets vitally influenced Joyce's early development, and consequently Stephen Dedalus's. As Andrew Gibson notes, "English literature self-evidently helped form Joyce's very rebellion against 'the English conventions' via Blake and Shelley, for example," and in Portrait, Stephen's self-image is certainly that of a Byronic hero.1 Jack Weaver goes so far as to argue that the Stephen of Portrait is "twice as Byronic as he is Shelleyan" while "out-Byroning Byron."2 This, I believe, fails to account for the significant influence of Shelley, who, as Jacques Aubert commented, "guided [Joyce's] first steps as a critic."3 Tracey Schwarze demonstrates that the aesthetic philosophy that Stephen develops in the final chapter of Portrait, despite its characterization as "applied Aquinas" (P 209), "owes as much to the influence of Shelley as to that of Aquinas," even though Shelley is only mentioned explicitly in connection with his metaphor of the "fading coal" of inspiration, "when the esthetic image is first conceived in [the] imagination" (P 213).4 As Schwarze points out, Stephen's definition of claritas, in [End Page 416] fact, denies Aquinas's theory of the objectivity of beauty in favor of Shelley's subjective power of "the mind of the artist."5 That Shelley's subtler influence would play a more integral role in Stephen's development is understandable considering that, as confirmed by Stanislaus Joyce, James Joyce "had progressed from his boyish hero-worship of Byron through Shelley to Blake."6 This acknowledged progression, along with the many references to Blake in Ulysses, may be why critics seem to agree with Aubert that "references to Shelley in the Portrait of the Artist need to be put into perspective," and why the references to Shelley in Ulysses have been generally overlooked or de-emphasized.7 Another reason may be that the majority of the direct references to Shelley in Ulysses are in "Scylla and Charybdis," where, as Andrew Gibson has shown, they are part of a sideways attack on Thomas Lyster's mentor, Edward Dowden, a Trinity College professor and authority on both Shakespeare and Shelley, who had strongly favored Matthew Arnold's famous pronouncement of Shelley as a "beautiful and ineffectual angel, beating in the void his luminous wings in vain."8 Stephen's performance in the library is seen from this perspective as an all-out attack on the reigning literary judgments of the day, using Shelley as a flank to the frontal assault with Shakespeare. But I believe the ties to Shelley, while by no means the only or even strongest influences in Ulysses, are more significant than the critical scholarship to date indicates. One important aspect of this influence can be gathered from the overriding importance Shelley placed on love, which Floyd Stovall summarizes as "the principle which actuates the life of the universe," and its primary actuator, Poetry.9 In A Defence of Poetry Shelley writes: The great secret of morals is Love; or a going...

Experimental and theoretical study of the electrical failures in a fault-tolerant direct-drive servovalve for primary flight actuators

The current paper deals with the study of the electrical failures in fault-tolerant flight actuators, with particular reference to the short circuits of the servovalve coils. A high-fidelity model of the servovalve of a modern fly-by-wire actuator is developed and validated through experiments, focusing attention on the characterization of the component dynamics in case of partial and total short circuits of the direct-drive motor coils. The servovalve model is then used to simulate a typical on-ground built-in-test procedure to determine the limit condition for the detection of a partial short circuit. Finally, once different possible combinations of short circuits are injected, the degradation of performances of the whole actuator is characterized through experiments, and the servovalve model is used to justify the test results, highlighting and discussing the effects of the failures on the system dynamics.

Development and experimental validation of real-time executable models of primary fly-by-wire actuators

The availability of practical real-time models of primary flight actuators is a key aspect for performing hardware-in-the-loop simulations of fly-by-wire flight control systems. The solution could be offered by empirical models tuned on experimental data, but this approach would imply that hardware-in-the-loop simulations could be performed only after the actuators have been designed, constructed, and tested. The alternative approach, to which this work refers, is to develop high-fidelity actuator models based on the component physics and to reduce their complexity by trying to obtain a compromise between accuracy of results and real-time execution requirements. In the paper, real-time models of a servo-hydraulic actuator for primary flight controls are developed, taking into account the basic features of the fly-by-wire implementation (the non-linear direct-drive servovalve dynamics, the structural compliance, the oil compressibility, the saturation of commands, and the digital controls) as well as other physical phenomena, which are often disregarded in hydraulic actuator modelling (the hinge play, the flow forces on the servovalve spool, and the laminar servovalve flow). The simulation results of models characterized by different levels of complexity are compared with experimental data obtained by testing the aileron actuator of a modern fly-by-wire aircraft, and the relative importance of the model characteristics is highlighted and discussed, providing useful guidelines about actuator model reduction for real-time applications.

CVT ratio control with consideration of CVT system loss

A modified CVT ratio map is proposed to obtain the improved fuel economy for a metal belt CVT. Since the CVT system loss, which occupies most of the drivetrain loss, depends on the engine speed, input torque, primary and secondary actuator pressure, a modified CVT ratio map is produced to realize the highest engine-CVT overall efficiency through the consideration of CVT system loss. The modified CVT ratio map is constructed with respect to the demanded vehicle power and present vehicle speed based on the steady state CVT system loss. Using the modified CVT ratio map, performance simulations are carried out using the dynamic models of the CVT powertrain. The simulation results indicate that the modified CVT ratio control provides improved engine-CVT overall system efficiency, and improves the fuel economy of the federal urban driving schedule by 4.9 percent.

Nonlinear Feedback Control of a Dual-Stage Actuator System for Reduced Settling Time

This brief presents a nonlinear control method for dual-stage actuator (DSA) systems to track a step command input fast and accurately. Conventional tracking controllers for DSA systems are generally designed to enable the primary actuator to approach the setpoint without overshoot. However, this strategy is unable to achieve the minimal settling time when the setpoints are beyond the secondary actuator travel limit. To further reduce the settling time, we design the primary actuator controller to yield a closed-loop system with a small damping ratio for a fast rise time and certain allowable overshoot. Then, a composite nonlinear control law is designed for the secondary actuator to reduce the overshoot caused by the primary actuator as the system output approaches the setpoint. The proposed control method is applied to an actual DSA positioning system, which consists of a linear motor and a piezo actuator. Experimental results demonstrate that our approach can further reduce the settling time significantly compared with the conventional control.

A Fault-Tolerant Model of Wireless Sensor-Actuator Network

In a wireless sensor and actuator network (WSAN), a group of sensor nodes, actuators, and actuation devices is geographically distributed and linked by wireless networks. Sensor nodes gather information for an event occurring in the physical world and send the sensed values to actuator nodes. Actuator nodes perform appropriate actions on actuation devices on receipt of sensed values from sensor nodes. Sensor nodes are a low cost, low-powered device with limited energy, computation, and wireless communication capabilities. Sensor nodes may suffer from arbitrary faults. Furthermore, wireless communications are unreliable due to collision and noise of a wireless channel and shortage of power of sensor nodes. Reliable efficient communication among sensor nodes, actuator nodes, and actuation devices is required in the presence of node and network faults. In order to realize the reliability and efficiency, we newly propose a multi-actuator/multi-sensor (MAMS) model where each sensor node sends sensed values to multiple actuator nodes and each actuator node receives sensed values from multiple sensor nodes for each event occurring in an event area. Even if some number of sensor nodes and actuator nodes are faulty and messages sent by sensor nodes and actuator nodes are lost, a required action can be performed on actuation devices. Actuator nodes are required to receive some messages from some number of sensor nodes to make a decision on what actions to be performed on actuation devices. Here, multiple actuator nodes may perform actions on receipt of sensed values. Multiple redundant executions of an action on each device have to be prevented and conflicting actions on each actuation device from multiple actuators have to be serialized. In this paper, we discuss a method to reliably and non-redundantly perform actions. On the other hand, there is one primary actuator node and multiple backup actuator nodes in the passive model. Only the primary actuator node performs actions. In this paper, we present a semi-passive coordination (SPC) model where not only primary but also backup actuator nodes receive messages from sensor nodes. Only one actuator node performs an action on an actuation device and a backup actuator node takes over the primary one if the primary gets faulty. In addition, multiple actuator nodes issue actions to each actuation device. We discuss how to resolve redundant execution of an action on an actuation device and serialize conflicting actions from multiple actuator nodes.

A magnetorheological actuation system: test and model

Self-contained actuation systems, based on frequency rectification of the high frequencymotion of an active material, can produce high force and stroke output. Magnetorheological(MR) fluids are active fluids whose rheological properties can be altered by the applicationof a magnetic field. By using MR fluids as the energy transmission medium in such hybriddevices, a valving system with no moving parts can be implemented and used to control themotion of an output cylinder shaft. The MR fluid based valves are configured in theform of an H-bridge to produce bi-directional motion in an output cylinder byalternately applying magnetic fields in the two opposite arms of the bridge. Therheological properties of the MR fluid are modeled using both Bingham plasticand bi-viscous models. In this study, the primary actuation is performed using acompact terfenol-D rod driven pump and frequency rectification of the rod motion isdone using passive reed valves. The pump and reed valve configuration alongwith MR fluidic valves form a compact hydraulic actuation system. Actuatordesign, analysis and experimental results are presented in this paper. A timedomain model of the actuator is developed and validated using experimental data.

Real-time loading actuator control for an advanced aerospace test rig

The growing complexity of aircraft systems requires that extensive testing be performed on dedicated test rigs to grant the necessary flight clearance and to provide troubleshooting of the problems that may arise during prototype flight trials. A new test rig is described herein, that was recently built to provide comprehensive testing of the flight controls, landing gear, and hydraulic systems of the M-346 advanced trainer aircraft. All these subsystems are connected together on the rig as in the real aircraft to ensure that the entire system operates on the rig exactly as on the aircraft. To that purpose, a high-performance force control system was developed to provide accurate dynamic loading of the primary and secondary flight control actuators, and the structure onto which the flight control actuators are mounted provides a mechanical load path with the same stiffness as in the real aircraft. The present paper describes the main characteristics of the test rig and puts particular emphasis on the force control system that makes use of an adaptive control law to provide a very accurate control of the force acting upon the actuators during fast transients.

New material extends seal life in aerospace applications

The newly engineered Turcon M30 non-abrasive material from Busak+Shamban has been shown to improve seal performance against tungsten carbide coated moving parts in primary flight controls and utility actuation systems.

MULTIRATE CONTROLLER FOR DUAL ACTUATED SERVOMECHANISM IN HARD DISK DRIVE

This paper concerns the design and implementation of a multirate controller for a dual-actuated servomechanism used in hard disk drive (HDD). The design following the decoupled master-slave structure is carried out in two steps. A state feedback controller is designed for the coarse primary actuator, the voice coil motor (VCM), to obtain minimal performance and stability, and the controller is suitable for merging with time-optimal control for large seek. Bandwidth achievable at this stage is restricted by the presence of resonant modes. The secondary stage follows the residual error from the VCM loop, and we want its gain to be as close to unity as possible for a wide range of frequency. Two loops are designed independently, which ensures stable performance in the event of secondary actuator failure. The controller is realized using multirate sampling. Effectiveness of the design is underscored using both simulation and experimental results.

Three-axis air-bearing based platform for small satellite attitude determination and control simulation

A frictionless environment simulation platform, utilized for accomplishing three-axis attitude control tests in small satellites, is introduced. It is employed to develop, improve, and carry out objective tests of sensors, actuators, and algorithms in the experimental framework. Different sensors (i.e. sun, earth, magnetometer, and an inertial measurement unit) are utilized to assess three-axis deviations. A set of three inertial wheels is used as primary actuators for attitude control, together with three mutually perpendicular magnetic coils intended for desaturation purposes, and as a backup control system. Accurate balancing, through the platform’s center of mass relocation into the geometrical center of the spherical air-bearing, significatively reduces gravitational torques, generating a virtually torque-free environment. A very practical balancing procedure was developed for equilibrating the table in the local horizontal plane, with a reduced final residual torque. A wireless monitoring system was developed for on-line and post-processing analysis; attitude data are displayed and stored, allowing properly evaluate the sensors, actuators, and algorithms. A specifically designed onboard computer and a set of microcontrollers are used to carry out attitude determination and control tasks in a distributed control scheme. The main components and subsystems of the simulation platform are described in detail.

High-bootstrap, noninductively sustained electron internal transport barriers in the Tokamak à Configuration Variable

Important ingredients of the advanced-tokamak route to fusion have been explored in depth in the Tokamak à Configuration Variable [F. Hofmann, J. B. Lister, M. Anton et al., Plasma Phys. Controlled Fusion 36, B277 (1994)] over the past two years. Using a uniquely powerful and flexible electron-cyclotron resonance heating (ECRH) system as the primary actuator, fully noninductive, steady-state electron internal transport barrier discharges have been generated with an electron-energy confinement time up to five times longer than in L mode, poloidal β up to 2.4, and bootstrap fraction up to 75%. Interpretative transport modeling confirms that the safety factor profile is nonmonotonic in these discharges. The formation of the barrier is a discrete event resulting in rapid and localized confinement improvement consistent with the time and location of magnetic-shear reversal. In steady state, however, the confinement quality appears to depend on the current gradient in a broader negative-shear region enclosed by the barrier, improving with increasing shear: in particular, the width and depth of the barrier can be controlled and finely tuned, along a magnetohydrodynamic-stable path, by manipulating the current profile with ECRH (six independently steerable 0.45 MW launchers). The crucial role of the current profile has been clearly demonstrated by applying small Ohmic current perturbations which dramatically alter the properties of the barrier, enhancing or reducing the confinement with negative and positive current, respectively, with negligible Ohmic heating. These results are in agreement with theoretical estimates: first-principle-based numerical simulations of microinstability dynamics and turbulence-driven transport predict a substantial suppression of turbulence and anomalous energy diffusivity near the location of the minimum in the safety factor.

Design and implementation of a dual-stage actuated HDD servo system via composite nonlinear control approach

We consider in this paper the design and implementation of a dual-stage actuated hard disk drive (HDD) servo system, in which an additional piezoelectric actuator is mounted on top of the conventional voice-coil-motor (VCM) actuator to provide a faster and finer response. More specifically, the dual-stage actuated HDD servo system consists of a primary VCM actuator and a secondary suspension piezoelectric microactuator. The VCM actuator is used to quickly move the read/write (R/W) head of the HDD servo system to a target track, whereas the microactuator is used to fine-tune the R/W head position when it is getting closer to the target. In our design, the primary actuator is controlled by a newly developed composite nonlinear feedback (CNF) control law, which has fast rise time and small overshoot, and the microactuator is controlled through a simple static gain together with a low-pass filter and a notch filter. Simulation and implementation results show that in track following, the dual-stage actuated HDD servo system has outperformed the single-stage actuated counterpart by more than 47% in settling time and by 39% in position error signal (PES) tests.

Ramifications of lubrication theory on imprint lithography

During photo-imprint lithography processes, such as Step and Flash Imprint Lithography, a fluid is displaced from the gap between a template and a substrate. Since the width of the template is much greater than the gap height from which the fluid is being expelled, lubrication theory approximations can be applied to the equations of continuity and momentum that describe the fluid behavior. Several methods of fluid delivery have been evaluated for Step and Flash Imprint Lithography, in particular, but are applicable to other imprint lithography techniques. This paper summarizes the forces generated using three primary template actuation schemes: constant velocity; constant applied force; constant applied pressure. It also compares the force required to displace a single droplet to that of a spincoated film, and the force to displace a fixed volume of fluid in a single droplet to that of the same volume divided into n identical droplets. The multi-droplet approach has been proposed and implemented as an effective alternative means of fluid delivery for dispensing low viscosity imprint solutions.

Thermally induced vibration control of composite plates and shells with piezoelectric activedamping

A coupled piezoelectric field is modelled with an expansion strain in the numericalformulation to analyse piezohygrothermoelastic laminated plates and shells. Finite elementactuator and sensor equations are derived using a nine-noded field consistent shallow shellelement. Thermally induced vibration control is attempted using piezoelectricallydeveloped active damping. The influence of piezoelectric anisotropy on active damping isevaluated, adopting a simple modelling technique. With 40% reduced actuation capabilityin the lateral direction, the directionally active lamina is observed to be equally efficient incontrolling the vibration. In general, the directionally active lamina is efficient ifthe primary actuation direction is oriented along the fibre direction or in thedirection of bending. The directional actuation appeared to be more effective inthe velocity feedback control for cantilevered plates and shells. However, in thesimply supported case, a balanced actuation effort is required to provide bettercontrollability, which can be achieved by tailoring the directional actuation. Theimportance of geometric curvature for the actuator performance is also highlighted.

Hierarchical Approach to Adaptive Control for Improved Flight Safety

Following failures of primary aerodynamic actuators, safe flight can be maintained by introducing alternative actuation systems, such as analytically redundant secondary aerodynamic surfaces and propulsion, for higher-priority stability and control augmentation tasks. An intelligent hierarchical flight control system architecture is presented that is designed using nonlinear adaptive synthesis techniques and online learning neural networks to enhance flight safety. Pseudocontrol hedging is used for proper adaptation in the presence of actuator saturation, rate limits, and failure. The hierarchical structure incorporates nonactive secondary actuation channels that are engaged after a failure of a primary control surface is encountered. The methodology requires only the knowledge that a failure in a specific actuator has occurred. A model of the failed aircraft, the failure type, and the failure size need not to be known: The neural network element of the secondary channel will adapt to the failed actuator effect. The secondary control channels are designed to account for the typically lower authority and degraded performance that can be expected with secondary actuation systems. The proposed hierarchical flight control architecture is attractive, in particular, as a retrofit to existing certified flight control systems for enhanced flight safety. The proposed flight control architecture is evaluated in a nonlinear flight simulation environment, demonstrating its retrofit features.