Point Actuators Research Articles

Understanding the Actuation Point Stiffness of Electromechanical Drum Brakes

<div>Electromechanically actuated drum brakes are one interesting option for the realization of brake-by-wire systems for future electric vehicles. A key characteristic for the design and control of electromechanical brake actuators is the actuation point stiffness, as this quantity relates the actuation force to the required actuator position. The various known approaches for the control of electromechanical brakes, which primarily focus on disc foundation brakes, typically rely on the stiffness curve at least to some extent. A transfer of these approaches to drum brakes is not straightforward, because the actuation point stiffness for drum brakes is much more complex compared to disc brakes. In particular, a strong hysteretic behavior is observed for the standing drum and a considerable change of the stiffness and hysteresis can be observed for the rotating drum. Although drum brakes have been used for decades these effects have not been thoroughly discussed in literature, yet. Hence, this article proposes a minimal model, which gives a fundamental understanding of the stiffness characteristics of drum brakes. The relation to measured stiffness curves is discussed in detail to provide an in-depth understanding of the drum brake behavior. Additionally, prospect is given to a reduced complexity model that is suitable for online identification and control.</div>

Design of an SMA-Based Actuator for Replicating Normal Gait Patterns in Pediatric Patients with Cerebral Palsy.

Cerebral Palsy refers to a group of incurable motor disorders affecting 0.22% of the global population. Symptoms are managed by physiotherapists, often using rehabilitation robotics. Exoskeletons, offering advantages over conventional therapies, are evolving to be more wearable and biomimetic, requiring new flexible actuators that mimic human tissue. The main objective behind this article is the design of a flexible exosuit based on shape-memory-alloy-based artificial muscles for pediatric patients that replicate the walking cycle pattern in the ankle joint. Thus, four shape-memory-alloy-based actuators were sewn to an exosuit at the desired actuation points and controlled by a two-level controller. The loop is closed through six inertial sensors that estimate the real angular position of both ankles. Different frequencies of actuation have been tested, along with the response of the actuators to different walking cycle patterns. These tests have been performed over long periods of time, comparing the reference created by a reference generator based on pediatric walking patterns and the response measured by the inertial sensors. The results provide important measurements concerning errors, working frequencies and cooling times, proving that this technology could be used in this and similar applications and highlighting its limitations.

Оптимизация раскрытия трансформируемого рефлектора космического базирования

The article discusses the issue of using optimal control algorithms to minimize bending vibrations of the spoke of a large-sized transformable reflector in the process of its deployment. This reduces transient time and improves the reliability and safety of the antenna deployment process. The creation of large-sized space-based systems is a current trend. Such systems allow solving a wide range of problems related to monitoring the Earth’s surface and space. At the same time, due to their size, the issue of structural defor-mation arises. A mathematical model is presented that describes the process of deployment the spokes taking into account transverse vibrations. Optimal control algorithms have been developed to minimize structural vibrations. For the stage of adjusting the radio-reflective net, an algorithm has been developed that minimizes energy costs. The results are confirmed by mathematical modeling and testing of algorithms on a laboratory unit. A method for adjusting a radio-reflective surface has been proposed, which makes it possible to reduce the number of actuators while maintaining the number of actuation points.

Design optimization and testing of a morphing leading-edge with a variable-thickness compliant skin and a closed-chain mechanism

Climate warming and the increased demand in air travels motivate the aviation industry to urgently produce technological innovations. One of the most promising innovations is based on the smoothly continuous morphing leading-edge concept. This study proposes a two-step process for the design of a morphing leading-edge, including the optimization of the outer variable-thickness composite compliant skin and the optimization of the inner kinematic mechanism. For the compliant skin design, an optimization of the variable thickness composite skin is proposed based on a laminate continuity model, with laminate continuity constraint and other manufacturing constraints. The laminate continuity model utilizes a guiding sequence and a ply-drop sequence to describe the overall stacking sequence of plies in different thickness regions of the complaint skin. For the inner kinematic mechanism design, a coupled four-bar linkage system is proposed and optimized to produce specific trajectories at the actuation points on the stringer hats of the compliant skin, which ensures that the compliant skin can be deflected into the aerodynamically optimal profile. Finally, a morphing leading-edge is manufactured and tested. Experimental results are compared with numerical predictions, confirming the feasibility of the morphing leading-edge concept and the overall proposed design approach.

A Virtual Mechanical System control law for energy transfer towards a single actuation point in [formula omitted] DOF buildings

Mitigating vibrations in engineering structures is of key interest, as they can lead to failure and/or discomfort. However, in some cases it is not feasible to actuate all the structure’s degrees of freedom, which makes vibration mitigation difficult. In this work, we investigate the addition of a single one-degree-of-freedom virtual mechanical system (VMS), as an active controller, to attract and mitigate the energy from an impulse load on the structure. To challenge the controller, an actuation point is chosen furthest away from the impact location. As it is implemented virtually, the coupling between the structure and VMS can be chosen freely. It is found that a skew-symmetric coupling generates a gyroscopic force that enables control over the structure’s mode shapes. Using this, the controller is tuned to achieve a beating phenomenon that attracts the vibration energy to the actuation location. A nonlinear damper, based on the slope of the envelope of the virtual velocity state, avoids reflection of energy to the structure and dissipates this unwanted energy. Furthermore, the virtual damper’s robustness to timing errors is investigated: damping too soon means an incomplete energy transfer to the VMS, damping too late leads to return of energy to the building. The tuning strategy of the VMS is applied to a 4 DOF and 60 DOF building benchmark. For comparison, a tuned mass damper (TMD) and a nonlinear energy sink (NES) are tuned as well. The VMS succeeds in decreasing the settling time significantly in both cases, while the performance of the passive TMD and NES is rather limited for this specific configuration.

Influence of actuation sequence on the snap-through process of composite multi-stable structures

In this paper, the impact of the actuation sequence on the snap-through process of a composite multi-stable structure composed of regular triangular modules was investigated. Using ABAQUS finite element simulation software, a finite element (FE) model of laminated plates was established, actuation points was selected on its surface, and bending moment loads were applied in different actuation sequences to induce the snap-behaviors of the structure. Based on the minimum load value for driving structure deforms, the actuation sequence laws of multi-stable structures were obtained. The most efficient and feasible actuation path for transitioning between different steady states was also achieved. It’s proved that the actuation paths are reasonable and feasible by the loading experiment. The research results of this paper can provide references for the design of multi-stable structures and the application modes of driving forces.

Focused Vibrotactile Stimuli From a Wearable Sparse Array of Actuators.

Wearable vibrotactile actuators are non-intrusive and inexpensive means to provide haptic feedback directly to the user's skin. Complex spatiotemporal stimuli can be achieved by combining multiple of these actuators, using the funneling illusion. This illusion can funnel the sensation to a particular position between the actuators, thereby creating virtual actuators. However, using the funneling illusion to create virtual actuation points is not robust and leads to sensations that are difficult to locate. We postulate that poor localization can be improved by considering the dispersion and attenuation of the wave propagation on the skin. We used the inverse filter technique to compute the delays and amplification of each frequency to correct the distortion and create sharp sensations that are easier to detect. We developed a wearable device stimulating the volar surface of the forearm composed of four independently controlled actuators. A psychophysical study involving twenty participants showed that the focused sensation improves confidence in the localization by 20% compared to the non-corrected funneling illusion. We anticipate our results to improve the control of wearable vibrotactile devices used for emotional touch or tactile communication.

Active Noise Control of Multirotor Advanced Air Mobility Vehicles

An active noise control technology is developed here to reduce the in-plane thickness noise associated with multirotor advanced air mobility Vehicles. The basic concept is that few actuators (e. g., microspeakers) are embedded into the blade surfaces. They emit a loading signal to cancel the thickness noise. This actuation signal is determined via the Ffowcs-Williams–Hawking (FWH) formula. We considered here two inline rotors, and we showed that the FWH-determined actuation signal can produce perfect cancellation at a point target. However, the practical need is to achieve noise reduction over an azimuthal zone, not just a single point. To achieve this zonal noise reduction, an optimization technique is developed to determine the required actuation signal produced by the on-blade distribution of embedded actuators on the two rotors. For the specific geometry considered here, this produced about 9 dB reduction in the in-plane thickness noise during forward flight of the two rotors. We further developed a technology that replaces using a point actuator on each blade by distributed microactuator system to achieve the same noise reduction goal with significantly reduced loading amplitudes per actuator.

Decentralized active damping control for aeroelastic morphing wing

This paper introduces a novel decentralized control design procedure for an aeroelastic morphing wing. The control goal is active damping of this flexible system. The model is developed as a multi-agent system with inherent interconnections between the agents. The control system then takes advantage of the model structure and interconnections rather than relying on the entire system's model. This brings benefits, especially with a growing number of agents where the control design dimension remains low. Therefore, the proposed control design is especially suitable for morphing wings with a large number of actuation points. The result is presented in the Linear Matrix Inequalities (LMIs) form. A numerical example shows the application of the proposed algorithm.

Artificial homeostatic temperature regulation via bio-inspired feedback mechanisms

Homeostasis comprises one of the main features of living organisms that enables their robust functioning by adapting to environmental changes. In particular, thermoregulation, as an instance of homeostatic behavior, allows mammals to maintain stable internal temperature with tightly controlled self-regulation independent of external temperatures. This is made by a proper reaction of the thermoeffectors (like skin blood vessels, brown adipose tissue (BAT), etc.) on a wide range of temperature perturbations that reflect themselves in the thermosensitive neurons’ activity. This activity is being delivered to the respective actuation points and translated into thermoeffectors’ actions, which bring the temperature of the organism to the desired level, called a set-point. However, it is still an open question whether these mechanisms can be implemented in an analog electronic device: both on a system theoretical and a hardware level. In this paper, we transfer this control loop into a real electric circuit by designing an analog electronic device for temperature regulation that works following bio-inspired principles. In particular, we construct a simplified single-effector regulation system and show how spiking trains of thermosensitive artificial neurons can be processed to realize an efficient feedback mechanism for the stabilization of the a priori unknown but system-inherent set-point. We also demonstrate that particular values of the set-point and its stability properties result from the interplay between the feedback control gain and activity patterns of thermosensitive artificial neurons, for which, on the one hand, the neuronal interconnections are generally not necessary. On the other hand, we show that such connections can be beneficial for the set-point regulation and hypothesize that the synaptic plasticity in real thermosensitive neuronal ensembles can play a role of an additional control layer empowering the robustness of thermoregulation. The electronic realization of temperature regulation proposed in this paper might be of interest for neuromorphic circuits which are bioinspired by taking the basal principle of homeostasis on board. In this way, a fundamental building block of life would be transferred to electronics and become a milestone for the future of neuromorphic engineering.

フレキシブルMEMSセンサを用いた圧縮機翼端ケーシング壁面における流れ角計測

In axial flow compressors, it is important to understand the detailed behavior because the tip leakage flow may leads to performance degradation and surge generation. However, since the tip clearance is very narrow with only a few millimeters of clearance, it is difficult to insert a probe and the flow angle cannot be measured by actuation point change in oil flow visualization.

Self‐Organization of Remote Reservoirs: Transferring Computation to Spatially Distant Locations

Soft materials generate rich and diverse dynamics that can be used as computational resources based on the framework of physical reservoir computing. Herein, a method that exploits the dynamic coupling between soft structures and a water medium to allow for the transfer of computation to spatially distant locations is proposed. This technique is implemented by introducing the concept of remote reservoirs that can autonomously alter their physical constituents in real time rather than using reservoirs with predefined, fixed physical constituents. These remote reservoirs self‐organize by including many ad hoc physical substrates in the environment, making the framework more flexible for soft robotic applications. Using a simple experimental platform consisting of silicone rubber strips containing embedded flexible strain sensors, it is demonstrated that the dynamics of passive silicone rubber strips located at a distance from the actuation point can be successfully exploited for computation through generalized synchronization realized via the medium of water. Future application scenarios are illustrated, in which the proposed technique is applied in emergency situations as a communication tool for transferring a message to a location that humans cannot easily access. For example, the technique could be applied to communicate with people trapped in submerged caves.

Propulsion enhancement of flexible plunging foils: Comparing linear theory predictions with high-fidelity CFD results

The fluid–structure interaction of a flexible plunging hydrofoil immersed in a current is solved numerically to analyze its propulsion enhancement due to flexibility at Reynolds number 10000. After validating with available experimental data, the code is used to assess analytical predictions from a linear theory. We consider large stiffness ratios, with high thrust enhancement by flexibility, and small mass ratios appropriate for underwater propulsion. The maximum thrust enhancement is observed at the first natural frequency, accurately predicted by the linear theory algebraically. The magnitude of the maximum thrust is over-predicted by the theory as the flapping amplitude increases. For large Strouhal numbers the flow becomes aperiodic, which for large enough amplitudes happens at frequencies below the natural frequency. But even at these Strouhal numbers, the linear theory predicts quite well the frequency of maximum thrust enhancement and optimal propulsive efficiency. We conclude that the linear theory constitutes a reliable and useful guide for the design of underwater flexible flapping-foil thrusters, and we provide a practical chart to easily select the optimal flapping frequency as a function of the actuation point, the stiffness and the mass ratios of the hydrofoil.

Refreshable Braille Module Using Cam Actuated Mechanism

Less than 3% of 145 million blind people in developing countries at present are literate [1]. At present, in most of the cases, speech output has been the medium for blind people to access materials. For content which require deep understanding such as technical texts etc., it is not an appropriate modality, moreover blind people are more accustomed to braille transcripts and adaptability issues to all audio resources is difficult. And thus, arises the need for a cheap, easily adaptable, less complex solution to the problem. Braille points are varied arrangements of raised dots representing characters which are identified by touch by visually impaired people. Here we discuss in detail, development of a dynamic/refresh-able Braille display which presents Braille points by the up-and-down movement of pins using a completely new, first of its kind, Cam actuated mechanism with just two actuation points instead of a standard 6 used by every single refresh-able braille board in the world at present. Two nested shafts having 8 arrays of precisely calculated and placed cam, each were responsible for keeping the pins in up and down state. The shafts were actuated using two micro-servo motors placed next to each other. X degree rotation of servo after transmission through gear and subsequently shaft resulted in a particular configuration. Henceforth calibration was done so that all braille alphabet could be produced with specific servo rotations.

Numerical Solution of the Vibration Suppression Problem for a Moving Web

Mechanical processes occurring in paper production are modeled. In a papermaking machine, paper moves in the form of a thin sheet. The characteristic thickness of a sheet varies from 0.1 mm (office paper) to 1 mm (cardboard). Every papermaking machine contains open segments where a paper web passes without mechanical support in its motion from one roller to another. On such segments, the web may lose stability, performing transverse vibrations, and, as a result, might tear. The possibility of reducing these vibrations with the help of various control actuators is explored. The transverse vibrations of a moving web with nonzero bending stiffness are modeled by a fourth-order inhomogeneous partial differential equation. The action of control actuators is modeled a function on the right-hand side of the equation. The vibration amplitude is assumed to be identical across the moving web. The vibration suppression problem is reduced to the minimization of a multivariable function. The solution of the problem splits into two stages: the solution of an initial-boundary value problem with a given control and the minimization of a multivariable function. A numerical method is proposed for solving the initial-boundary value problem. The fourth-order differential equation is reduced to a system of two second-order differential ones. The latter are simplified by changing the sought functions. The resulting equations are approximated by a finite-difference scheme, which is proved to be absolutely stable. This scheme is solved using block Gaussian elimination. The multivariable function is minimized by applying the Hooke–Jeeves method. Examples of computations are given for actuators of three types, namely, point actuators, actuators acting on a web segment, and actuators acting along the entire web.

Artificial Neural Networks-Extended Great Deluge Model to predict Actuators Displacements for a Morphing Wing Tip System

Resin-based fiber composite materials have received attention in aerospace composite engineering, particularly in aircraft morphing structures, due to their high mechanical characteristics, such as stiffness, and because of their potential to highly reduce the structural mass of modern aircraft. Aircraft morphing is referred to as the ability of an aircraft’s surface to change its geometry in flight. The modelling of a dynamic morphing wing system is here studied. The morphing wing was controlled using four electric actuators situated inside of the wing model. The main role of these actuators was to modify the wing upper surface shape designed and manufactured with a flexible material, so that the laminar-to-turbulent flow transition point can move closer to the wing trailing edge, thus causing a minimum viscous drag, for various flow conditions. To determine the skin deflections in the four actuators points, both LVDT and dial indicator gages were positioned on the wing. Four Linear Variable Differential Transducers (LVDTs) were used to indicate the positions of the four actuators, and four Dial Indicators gages were positioned on the wing to measure the real deflections of the flexible composite skin in the four actuation points. The relationship between the Dial Indicators’ values and the LVDTs’ values for a same set-point command signal had a nondeterministic and unpredictable behavior (not a linear one). The values of the displacements given by the LVDTs were different than the values given by the Dial Indicators. In this paper, an Artificial Neural Network (ANN) model was investigated created with the aim to predict the displacements of the wing upper surface skin in real time using four actuators. The proposed model was trained using the Extended Great Deluge (EGD) algorithm.

Design of a Segmented Mirror with a Global Radius of Curvature Actuation System: Contributions of Multiple Surrogates

Due to fabrication difficulties, separately-polished segmented mirrors cannot meet the co-phasing surface shape error requirements in the segmented telescope system. Applying the global radius of curvature (GRoC) actuation system for the individual segments has become an effective solution in space-based telescopes. In this paper, we designed a segmented mirror with a GRoC actuation system. The direct optimization by numerical simulations has low computational efficiency and is not easy to converge for optimizing the actuation point’s position on the segmented mirror. For this problem, three common surrogates, including polynomial response surface (PRS), radial basis function neural network (RBFNN), and kriging (KRG), were summed to propose the multiple surrogates (MS) which have the higher approximate ability. The surrogates were then optimized through the multi-island genetic algorithm (MIGA), and the segmented mirror met the design requirement. Compared with direct optimization through numerical simulations, the results show that the proposed multiple-surrogate-based optimization (MSBO) methodology saves computational cost significantly. Besides, it can be deployed to solve other complex optimization problems.

Comparison of smart panels for tonal and broadband vibration and sound transmission active control

ABSTRACT This paper presents a comprehensive overview of the principal features of smart panels equipped with feed-forward and feedback systems for the control of the flexural response and sound transmission due respectively to tonal and to stochastic broadband disturbances. The smart panels are equipped with two types of actuators: first, distributed piezoelectric actuators formed either by small piezoelectric patches or large piezoelectric films bonded on the panels and second, point actuators formed by proof-mass electromagnetic transducers. Also, the panels encompass three types of sensors: first, small capacitive microphone sensors placed in front of the panels; second, distributed piezoelectric sensors formed by large piezoelectric films bonded on the panels and third point sensors formed by miniaturized accelerometers. The proposed systems implement both single-channel and multi-channel feed-forward and feedback control architectures. The study shows that, the vibration and sound radiation control performance of both feed-forward and feedback systems critically depends on the sensor-actuator configurations.

Development and experimental verification of an adaptive structure for phased antenna array using SMA bunch

An adaptive structure for a phased antenna array is proposed using shape memory alloy (SMA) as an actuation component for the plate flatness control. Fiber Bragg Grating (FBG) sensors are designed for plate strain measurement, and a strain displacement transformation method is introduced to obtain the deformation field from the strain measurement data. The deformation field is then used to determine the correction loads of actuation points using integer nonlinear programming analysis. An adaptive prototype for the phased antenna array plate is developed with the distribution of monitored, actuation, and load points. Numerical simulations are performed to demonstrate the detailed process of the strain displacement transformation method. Moreover, the method is further discussed after testing the adaptive plate structure with the digital image correlation (DIC) technology. Finally, the reliability and efficiency of the proposed active control scheme are validated with an experimental setup. The study promotes the engineering application of the active control concept in large scale phased antenna arrays.

Controlling Flow Separation on a Thick Airfoil Using Backward Traveling Waves

Large-eddy simulations (LESs) of low-Reynolds-number flow () over a NACA0018 airfoil are performed to investigate flow control at the stall angle of attack (15 deg) by low-amplitude surface waves (actuations) of different types (backward/forward traveling and standing waves) on the airfoil’s suction side. It is found that the backward (toward downstream) traveling waves, inspired from aquatic swimmers, are more effective than forward traveling and standing wave actuations. The results of simulations show that a backward traveling wave with a reduced frequency (, where is frequency; , chord length; and , free flow velocity), a nondimensional wavelength (, where is dimensional wavelength), and a nondimensional amplitude (, where is dimensional amplitude) can suppress stall. In contrast, the flow over the airfoil with either standing or forward traveling wave actuations separates from the leading edge similar to the baseline. Consequently, the backward traveling wave creates the highest lift-to-drag ratio. For traveling waves at a higher amplitude (), however, the shear layer becomes unstable from the actuation point and creates periodic coherent structures. Therefore, the lift coefficient decreases compared with the low-amplitude case.