Pair Of Actuators Research Articles

A Low-Cost Lateral Active Suspension System of the High-Speed Train for Ride Quality Based on the Resonant Control Method

This paper focuses on the low-cost configuration of the lateral active suspension system for the high-speed train. First, the full-scale railway vehicle dynamics with 17-degree-of-freedom are introduced, where the actuator saturation, suspension deflection, and random and periodic track irregularities are considered. Then, based on the internal model principle, some classic active vibration control methods, e.g., the PID, positive position feedback, repetitive, and resonant controls, are unified as an internal model (IM)-based form and an IM-based resonant control is further presented. After that, to suppress various vibrations, three principles are presented to set the damping ratio and natural frequency of the IM-based resonant controller according to the properties of the controlled plant and/or the external disturbances. In consequence, an active suspension with the IM-based resonant controller is designed to improve the ride quality of the high-speed train, where the $H_{\infty }$ method is used to calculate the unique gain. Moreover, the configuration of the active suspension is low cost and consists of two independent control systems, where one control system only has a pair of actuators and an accelerometer. Finally, the random and periodic track irregularities are employed to show the efficiency of the proposed resonant-control-based active suspension by comparing with the linear quadratic Gaussian (LQG) and $H_{\infty }$ controllers.

Optimization of shape control of a cantilever beam using dielectric elastomer actuators

Dielectric elastomer (DE) is a kind of smart soft material that has many advantages such as large deformation, fast response, lightweight and easy synthesis. These features make dielectric elastomer a suitable material for actuators. This article focuses on the shape control of a cantilever beam by using dielectric elastomer actuators. The shape control equation in finite element formulation of the cantilever beam partially covered with dielectric elastomer actuators is derived based on the constitutive equation of dielectric elastomer material by using Hamilton principle. The actuating forces produced by dielectric elastomer actuators depend on the number of layers, the position and the actuation voltage of dielectric elastomer actuators. First, effects of these factors on the shape control accuracy when one pair or multiple pairs of actuators are employed are simulated, respectively. The simulation results demonstrate that increasing the number of actuators or the number of layers can improve the control effect and reduce the actuation voltages effectively. Second, to achieve the optimal shape control effect, the position of the actuators and the drive voltages are all determined using a genetic algorithm. The robustness of the genetic algorithm is analyzed. Moreover, the implications of using one pair and multiple pairs of actuators to drive the cantilever beam to the expected shape are investigated. The results demonstrate that a small number of actuators with optimal placement and optimal voltage values can achieve the shape control of the beam effectively. Finally, a preliminary experimental verification of the control effect is carried out, which shows the correctness of the theoretical method.

Optimal Placement Strategy of Multiple Patches for Active Vibration Control of Cantilever Beams Based on Modal Strain

Identification of a proper location for sensor actuator pair is very important for multimode vibration control of beams. A lot of research work is carried by various researchers, for the optimization of actuators and sensors location. Various techniques and approaches have been used, but there are two broad approaches. In the first approach the placement of patches is combined with controller parameters, while in second approach, the locations are achieved independently of controller parameters. For achieving the best vibration control, the placement of the piezopatches should be in the region of maximum strain location. This paper presents, controller independent, simplified optimal patch placement strategy, on cantilever beams, based on modal strain profile. The modal strain patterns obtained from FE analysis of beams, are utilized to devise a strategy for identifying the locations of piezopatches. The effectiveness of strategy adopted for optimal location is compared with the results obtained from a controller dependent placement methodology employed by previous researchers. It is found that the proposed methodology is in agreement with the work carried out earlier.

Dynamics and control of the vortex flow behind a slender conical forebody by a pair of plasma actuators

Detailed particle-image-velocimetry (PIV) and surface pressure measurements are presented to study the vortex flow behind a slender conical forebody at high angles of attack. The results confirm the existence of two randomly appearing mirror imaged asymmetric bi-stable states of the separation vortices, giving rise to large side force and moment. A pair of carefully designed dielectric barrier discharge plasma actuators mounted near the apex and on both sides of the conical body are used to manipulate the vortex flow and thus provide control of the side forces on the body without using flaps. By making use of a duty-cycle actuation scheme that alternately actuates the port and starboard plasma actuators and optimizing the duty-cycle frequency, the present work demonstrates the feasibility of achieving a nearly perfect linear proportional control of the side force and moment in response to the duty-cycle ratio. Phase-locked PIV and surface pressure measurements are used to study the unsteady dynamic evolution of the flow within one duty-cycle actuation to reveal the flow control mechanism. It is found that under the duty-cycle actuation with the optimized frequency, the vortex flow essentially follows the plasma actuation by alternating between the two bi-stable states controlled directly by the duty-cycle ratio.

Stochastic Channel Allocation for Nonlinear Systems with Markovian Packet Dropout

This paper addresses a channel scheduling problem for group of dynamically decoupled nonlinear subsystems with actuators connected through digital communication channels and controlled by a centralized controller. Due to the limited communication capacity, only one channel can be activated and hence there is only one pair of sensor and actuator can communicate with the controller at each time instant. In addition, the communication channels are not reliable so Markovian packed dropout is introduced. A predictive control framework is adopted for controller/scheduler co-design to alleviate the performance loss caused by the limited communication capacity. Instead of sending a single control value, the controller sends a sequence of predicted control values to a selected actuator so that there are control input candidates which can be fed to the subsystem when the actuator does not communicate with the controller. A stochastic algorithm is proposed to schedule the usage of the communication medium and sufficient conditions on stochastic stability are given under some mild assumptions.

Dynamic Modeling and Analysis of a Rotating Piezoelectric Smart Beam

In active vibration control study, piezoelectric actuators and sensors are bonded on the surface of a beam. They can change the frequency and modal characteristics of the system. This paper presents an analysis of the frequency response to a rotating piezoelectric smart beam. Hamilton’s principle along with the assumed mode method are employed to derive the governing equations of the first-order approximate coupling model for the piezoelectric smart beam. The coupling is taken into account as the second-order coupling effect of the axial elongation caused by the transverse displacement of the beam. Then, the equations are transformed into a dimensionless form after identifying the necessary parameters. The dimensionless natural frequencies of the piezoelectric smart beam corresponding to the bending and stretching vibrations are obtained through a numerical simulation, with comparison made of those of the beam with no actuator or sensor. Furthermore, the implication is investigated of the structural parameters and bond location on the piezoelectric actuators and sensors. Besides, the common case of a smart beam bonded with multiple pairs of piezoelectric actuators and sensors is studied, and the effects of the first natural frequency and tip deformation are analyzed. The research provides a theoretical reference for the optimization of structural parameters and location of piezoelectric actuators and sensors, thereby preventing the resonance when the excitation frequency is approximately equal to the natural frequency of the beam.

Adjusting the natural stiffness of a pneumatic powered exoskeleton designed as a virtual reality haptic device

This study describes the natural stiffness of a pneumatic powered exoskeleton arm, designed as a haptic device in virtual reality applications. It is important for the haptic device to provide a natural, safe, and comfortable physical mutual human–robot interaction as well as realism for the haptic feedback. To meet these requirements, an exoskeleton possessing an actuation system based on pneumatic artificial muscles and feedforward impedance control is presented. A natural stiffness controller is included to passively adjust the desired stiffness of the exoskeleton. The parameters of the actuation system that determine the natural exoskeleton stiffness are analyzed. A scheme is constructed for joint torque control and end-effector stiffness adjustment under the antagonistic action of the pairs of pneumatic actuators. An optimization-based approach is created for specifying the parameters determining the natural stiffness of the exoskeleton arm. Computer simulations are conducted for a preliminary assess...

Experimental study of local and modal approaches to active vibration control of elastic systems

Two different methods, local and modal, are suggested to control systems with distributed parameters, each of them having its own advantages and drawbacks. The aim of the present research is to carry out experiments aiming in comparison of these 2 methods for the problem of suppression of forced bending vibrations of a thin metal beam. Two pairs of piezoelectric sensors and actuators are attached to the beam in each control system considered. Their locations are chosen so as to provide the most efficient measurement and excitation of the first and second vibration modes of the beam. Frequency methods of the automatic control theory are employed to design stable control systems that can efficiently suppress bending vibrations of the beam with the first and second resonance frequencies. As a result, control systems with the desired performance are created on the basis of both local and modal methods. The obtained modal system works efficiently for both resonances, whereas the local systems demonstrate appropriate performance either at the first or at the second resonance frequency only. This difference is due to the fact that in the case of modal control, each control loop corresponds to a particular vibration mode and can be designed to provide optimal performance at the required frequency. The performed benchmark study demonstrates the advantages of the modal method over the local one for the cases where it is necessary to suppress vibrations in the frequency range that contains more than one resonance frequency of the control object.

Active vibration control of a beam instrumented with MWCNT/epoxy nanocomposite sensor and PZT-5H actuator, robust to variations in temperature

Multi walled carbon nano tube (MWCNT)/epoxy nanocomposite strain sensor and piezoelectric actuator pair are used in active vibration control (AVC) of a smart cantilevered beam. Due to different coefficients of thermal expansion of MWCNT and epoxy, the resistance of carbon nanotube/epoxy based strain sensor changes nonlinearly with change in temperature. The temperature dependence of CNT based strain sensor is modelled by fitting a polynomial curve on the experimentally obtained characterization data of CNT/epoxy strain sensor. Using augmented constitutive equations of piezoelectricity, finite element model of smart cantilevered beam instrumented with collocated nanocomposite strain sensor and PZT-5H actuator is derived. Effect of temperature on PZT-5H actuator is also considered in derivation of the control law. Active vibration control of the first mode of a smart cantilevered beam instrumented with collocated CNT based strain sensor and PZT-5H actuator is performed at ambient temperature and at temperature slightly away from the ambient temperature for two cases: (1) without considering the temperature dependence of CNT composite strain sensor in Kalman observer and (2) considering the temperature dependence of CNT composite strain sensor in Kalman observer. Simulations are also performed to visualize the behaviour of smart beam when the beam is subjected to a temperature impulse. This paper suggests a novel AVC strategy using MWCNT/epoxy strain sensor and PZT-5H actuator patch that is robust to variations in temperature.

A soft wearable robot for the shoulder: Design, characterization, and preliminary testing.

In this paper, we present a soft wearable robot for the shoulder which has the potential to assist individuals suffering from a range of neuromuscular conditions affecting the shoulder to perform activities of daily living. This wearable robot combines two types of soft textile pneumatic actuators which were custom developed for this particular application to support the upper arm through shoulder abduction and horizontal flexion/extension. The advantage of a textile-based approach is that the robot can be lightweight, low-profile, comfortable and non-restrictive to the wearer, and easy to don like an item of clothing. The actuator's ability to fold flat when not in use allows the robot to be almost invisible under clothing, potentially allowing the user to avoid any stigma associated with using assistive devices in public. To abduct the arm, a textilebased pneumatic actuator was developed to fit within the axilla to push the arm upwards, while a pair of smaller actuators pivot the abduction actuator to allow for horizontal extension and flexion. The individual textile actuators were experimentally evaluated before being integrated into a wearable garment. Human subject testing was performed to evaluate the ability of the robot to assist the arm by monitoring changes in biological muscle activity when comparing the robot powered on and off. Preliminary results show large reductions in muscular effort in targeted muscles, demonstrating the feasibility and promise of such a soft wearable robot for the shoulder.

Investigation of dynamic thermal behaviors of an electrothermal micromirror

It is well known that the heat transfer at microscale is quite different from that at macroscale, but the dynamic thermal behavior of micro-actuators with movable microstructures still lacks comprehensive investigation. This work presents a thorough study on thermal behaviors of an electrothermally actuated scanning micromirror, which has a 1mm×1mm central mirror plate supported on four sides by four pairs of electrothermal bimorph actuators. The heat transfer from the thermal actuator to the ambience, including the substrate and the environmental air, are investigated experimentally with several different driving powers and various frequencies under natural convection, forced convection, and in vacuum. The results indicate that the heat conduction dominates the heat transfer process of electrothermal bimorph actuators, while the convection has little impact on the overall heat transfer even under strong forced convection. Furthermore, an equivalent circuit model of the electrothermal micromirror is developed and experimentally verified, from which the effective heat transfer coefficient of the electrothermal bimorphs is extracted to be in the range from 1900 to 2282W/(m2K), which is one to two orders of magnitude larger than that at macroscale.

Electromagnetic actuators for controlling flexible cantilever beams

Electromagnetic actuators are very important for scientific and industrial applications. Their use may vary within a wide range of possibilities due to their most important feature: the ability to apply known and controllable forces to elements or structures without contact. In this article, an application within this range is analyzed: a proportional-integral-derivative (PID) controller is used with a pair of actuators to control the dynamic forced response of a flexible cantilever metallic beam and to keep it at a given reference position. In order to achieve this objective, both the actuators and the controller need to be adjusted. For the actuators, the main parameters evaluated consider mounting particularities, such as the differential assembly and the influence of the air-gap distance over the magnetic flux density and the magnetic force provided. Next, a brief review of PID controllers is presented, highlighting 5 tuning methods, and their effects on relevant parameters of the electromagnetic system (such as the cutoff frequency). Finally, results focus on the comparative efficiency of the PID tuning methods to reduce the vibration amplitude of the beam bending modes. The results show that the Ziegler–Nichols modified for some-overshoot and no-overshoot methods are the best choices.

Design and Fabrication of a 2-Axis Electrothermal MEMS Micro-Scanner for Optical Coherence Tomography

This paper introduces an optical 2-axis Micro Electro-Mechanical System (MEMS) micromirror actuated by a pair of electrothermal actuators and a set of passive torsion bars. The actuated element is a dual-reflective circular mirror plate of 1 in diameter. This inner mirror plate is connected to a rigid frame via a pair of torsion bars in two diametrically opposite ends located on the rotation axis. A pair of electrothermal bimorphs generates a force onto the perpendicular free ends of the mirror plate in the same angular direction. An array of electrothermal bimorph cantilevers deflects the rigid frame around a working angle of 45 for side-view scan. The performed scans reach large mechanical angles of 32 for the frame and 22 for the in-frame mirror. We denote three resonant main modes, pure flexion of the frame at 205 , a pure torsion of the mirror plate at 1.286 and coupled mode of combined flexion and torsion at 1.588 . The micro device was fabricated through successive stacks of materials onto a silicon-on-insulator wafer and the patterned deposition on the back-side of the dual-reflective mirror is achieved through a dry film photoresist photolithography process.

The LQR Control Active of Smart Plate Based on the Finite Element Method

This paper presents a numerical study pertaining to on the active vibration control (AVC) of the 3-D rectangle simply supported plate bonded of the piezoelectric sensor/ actuator pairs. AVC is a large area of interest either in all sections of industry or in research. One way to control the vibration of dynamic systems is by using piezoelectric materials. A finite element method (FEM) analysis is used to model the dynamic behavior of the system. The frequencies of the isotropic pate and a smart structure are verified by the comparison between the analytical calculations and simulation. A LQR controller is designed based on the independent mode space control techniques to stifle the vibration of the system. The change in the sizes of the patches was a clear impact on the control results, and also in the values of the voltage in actuator. The results were established by simulating in ANSYS and MATLAB.

Influence of Actuating Position on Asymmetric Vortex Control With Nanosecond Pulse DBD Plasma Actuators

An experimental study of flow control over conical body by nanosecond pulse dielectric barrier discharge (NS-DBD) plasma actuation at Re $_{D} = 3.09 \times 10^{5}$ ( ${v} = 42$ m/s) is presented. First, the fundamental characteristics and control mechanisms of the plasma actuator were studied in the quiescent atmosphere. NS-DBD plasma actuator is an economical effective device because of its high discharge voltage/frequency ( $\sim 20$ kV/20 kHz), but short pulse duration time ( $\sim 20$ ns). Plasma actuators with different geometries were studied using the Schlieren technique. On the microsecond time scale, combination compression waves that consisted of a hemisphere wave and a planar wave were generated by rapid gas heating. The propagation velocity produced during the initial stage (10–40 $\mu \text{s}$ ) can potentially reach the sonic level ( $\sim 350$ m/s). On the millisecond time scale, two starting vortices rolled up from two opposite directions, and then developed into one perturbation downstream. NS-DBD plasma actuation influences the flow by rapid localized heating and transferring energy to the near-wall gas. In the wind tunnel experiment, a pair of NS-DBD plasma actuators mounted symmetrically on the surface of the model apex were applied to control the asymmetric vortex flow field. Actuators were, respectively, aligned along the line of azimuth angles of $\theta = \pm 80^{\circ }$ , ±90°, and ±100°, under positive and negative discharges. The test results include the pressure distribution sampled over the measurement station and the calculated lateral force coefficient. The efficacy of NS-DBD plasma actuation for controlling the asymmetric vortex over conical body was demonstrated with arrangements $\theta = \pm 80^{\circ }$ and $\theta = \pm 90^{\circ }$ . The results suggest that the actuator should be set before the suction peak point. When the flow started to accelerate and separate, the small perturbation created by NS-DBD could hardly control the flow. Pressure distributions under plasma actuation with different discharge directions indicate that the control power of NS-DBD is directional and is located along the discharge direction. The actuation with positive discharge delays the separation, whereas the actuation with negative discharge fixed separates the flow.

Shared inductor hybrid topology for weight constrained piezoelectric actuators

This paper presents a new circuit topology designed to minimise the weight of the control circuit required to actuate multiple piezoelectric actuators. It can independently set the phase and bias voltage on each piezoelectric actuator through the use of a single inductor. This is highly desirable in weight constrained applications such as unmanned aerial vehicles as the ferroelectric material required for the inductor is heavy. Furthermore, the circuit topology can also use the same inductor to generate the high bias voltage required to drive the actuators. The full system has been verified in PSpice and a pair of piezoelectric actuators have been successfully driven using off the shelf components.

Flutter and buckling characteristics and active control of sandwich panels with triangular lattice core in supersonic airflow

Abstract Sandwich structures with lattice core are novel composite structures, but the aeroelastic behaviors of them have not been fully studied. This paper is devoted to investigate the flutter and buckling properties of sandwich panels with triangular lattice core in supersonic airflow, and the active flutter and buckling control are also carried out, which can provide theoretical basis for the use of sandwich structures in the design of aircrafts. The unsteady aerodynamic pressure is evaluated by the supersonic piston theory in which the yawed flow angle is taken into account. Hamilton's principle with the assumed mode method is applied to formulate the equation of motion of the structural system. The active controller is designed by the displacement feedback method. Aeroelastic characteristics of the sandwich panels are studied, and the influences of the aerodynamic pressure on the frequency and mode shape of the panel are analyzed. The effects of yawed flow angle on the flutter properties of the sandwich panel are also analyzed. When considering the external in-plane load, the buckling behaviors of the sandwich panel are investigated. Moreover, the flutter and buckling properties between the sandwich and equivalent isotropic panels are compared to show the superior aeroelastic properties of the sandwich panels. The effects of piezoelectric patch placements on the active flutter control are analyzed. The optimal locations of piezoelectric actuator and sensor pairs are obtained by the genetic algorithm. The present study verifies that the sandwich structures have different aeroelastic and flutter suppression properties, which is useful in the research of lightweight sandwich materials.

Possibility of binaural production by means of bone conduction actuators

A pair of bone conduction actuators is used for music reproduction as replacement of headphone. Because of strong inter-aural coupling, it is though the stereophonic reproduction is not easy to realize by bone conduction actuators. Haim Sohmera, et al. 2000, reported that “there is no need to vibrate bone in order to obtain 'bone conduction' response.” They have shown a fluid pathway from bone to ear. The coupling between left and right side stimuli by bone conduction actuators set at head-of-mandible or mastoid is occurred not only due to bone but also fluid. On the other hand, when we are listening the music by bone conduction actuators, we can enjoy the some extent of special image, at least some extend of lateralization. The authors are examined the possibility of binaural production by means of inter-aural time and intensity trading using a pair of bone conduction actuators. Results of psycho-acoustical experiment indicate that the trading phenomenon between time and intensity is observed around 1000...

Bioinspired Segment Robot with Earthworm-like Plane Locomotion

In this paper, a miniaturized segment robot using solenoids is developed to mimic the plane locomotion of earthworms. The bioinspired robot is composed of five segmented bodies, and one segment has two solenoid actuators. This robot can move linearly and it can also turn due to the pair of solenoid actuators that facilitate the earthworm-like peristaltic locomotion. We have designed a miniaturized solenoid with a permanent magnet plunger in order to increase the total electromagnetic force. A theoretical analysis is performed to predict the linear and turning motions of each segment, and the optimal profiles of input signals are obtained for fast locomotion. Experiments are then conducted to determine the linear and turning motions of the segment robot. It takes about 0.5 s for the five segments to complete one cycle of the peristaltic locomotion. In experiments, the segment robot is shown to have the linear and angular velocities of 27.2 mm·s−1 (0.13 body-length per second) and 2 degrees per second, respectively.

Sensor enabled closed-loop bending control of soft beams

Control of soft-bodied systems is challenging, as the absence of rigidity typically implies distributed deformations and infinite degrees-of-freedom. In this paper, we demonstrate closed-loop control of three elastomer beams that vary in bending stiffness. The most stiff beam is comprised of a single prismatic structure made from a single elastomer. In the next beam, increased flexibility is introduced via an indentation in the elastomer, forming a joint. The most flexible beam uses a softer elastomer in the joint section, along with an indentation. An antagonistic pair of actuators bend the joint while a pair of liquid–metal-embedded strain sensors provide angle feedback to a control loop. We were able to achieve control of the system with a proportional–integral–derivative control algorithm. The procedure we demonstrate in this work is not dependent on actuator and sensor choice and could be applied to to other hardware systems, as well as more complex multi-joint robotic structures in the future.