Actuator Position Research Articles

High-integrated micro permanent magnet linear actuator positioning system

A tunnel magnetic resistance (TMR) sensor is a magnetic detection sensor with low power consumption and high sensitivity. The TMR sensor has promising applications in the position detection of micro permanent magnet linear actuators since the surrounding magnetic field of the micro actuator in this paper will be changed by its movement. Firstly, according to the air-gap magnetic field distribution characteristics of the micro permanent magnet linear actuator and the detection principle of the TMR sensor, the integrated installation parameters of TMR sensors were determined. Then, with the help of TMR technology, the backpropagation neural network (BPNN) algorithm and improved BPNN using particle swarm optimization (PSO) algorithm were used to study the position identification strategy of the slider, and the algorithm strategy with the minimum error was selected. Finally, the experimental results show that the slider position identification strategy based on the PSO-BPNN algorithm can achieve position tracking error within 0.1 mm under the given step position tracking and sinusoidal position tracking, and the movements can be repeated well.

Optimal Pneumatic Actuator Positioning and Dynamic Stability using Prescribed Performance Control with Particle Swarm Optimization: A Simulation Study

This paper introduces an optimal control strategy for pneumatic servo systems (PSS) positioning using Finite-time Prescribed Performance Control (FT-PPC) with Particle Swarm Optimization (PSO). Pneumatic servo systems are widely used in industrial automation, as well as medical and cybernetics systems that involve robotics applications. Precision in pneumatic control is crucial not only for the sake of efficiency but also safety. The primary goal of the proposed control strategy is to optimize the convergence rate and finite time of the prescribed performance function in error transformation of the FT-PPC, as well as the Proportional, Integral and Derivative (PID) controller as the inner-loop controller for this system. The study utilizes a dynamic model of a pneumatic proportional valve with a double-acting cylinder (PPVDC) as the targeted plant and performs simulations with a multi-step input trajectory. This offline tuning method is essential for such nonlinear systems to be safely optimized, avoiding major damage to the real-time fine-tuned works on the controller. The results demonstrate that the proposed control strategy surpasses the performance of FT-PPC with a PID controller alone, significantly improving the system's performance, including suppressing overshoot and oscillation in the responses. Further validation through the actual system of PPVDC using the fine-tuned values of FT-PPC and PID with PSO is a future task and more challenging to come, as hardware constraints may vary with different environments such as temperatures.

Precise Configuring of Actuators/Sensors for Active Control of Sound Quality in Cabs with Modal Vibration Energy and LA-PSO

Active control of structural modal vibration is an effective strategy to enhance the sound quality of cabs in commercial vehicles. However, accurate determination of the positioning and quantity of modal active control sensors and actuators is crucial for cabs with intricate structures, owing to the presence of multiorder modes and their coupling. The study presented herein focuses on the cab of a commercial vehicle and contemplates the features of the irregular large-space structure of the cab. By capitalizing on the modal frequency and mode shape of the cab, utilizing the piezoelectric control principle and modal vibration energy as the assessment index, an advanced multimode composite control criterion is postulated to ascertain the configuration of primary sensors and actuators. The particle swarm optimization (PSO) objective function is constructed to accomplish the optimal position matching of the actuator/sensor, using the multimodal surface velocity vector of the vibration sensor as the core parameter. Furthermore, an improved linear adaptive particle swarm optimization (LA-PSO) technique is advanced to satisfy the requirements of optimal convergence performance and accuracy of the complex cab structure. The optimization culminates in a 9 × 9 multichannel active control scheme for determining the optimal position of the actuators/sensors. This investigation provides a technical foundation for the active control of sound quality in automotive cabs and presents an innovative method for implementing effective noise control systems in large-scale machinery and equipment.

Experimental investigation of synthetic jet control of wing rock for a flying wing aircraft

Flying wing aircraft easily experience wing rock due to the lack of lateral-directional stability, which causes serious challenges to flight control and safety. Thus, it is necessary to reduce the wing rock amplitude or reduce the mean roll angle by additional control. For a flying wing model with a 65° leading-edge sweep, we propose a strategy using an array of synthetic jet actuators to control the wing rock. The control effect and mechanism are studied by attitude measurement and particle image velocimetry measurement in a wind tunnel; the results confirm that the synthetic jet can effectively change the trim position of the wing rock. The control effect is affected by the angle of attack, Reynolds number, actuation position, actuation voltage, and frequency. In general, downstream actuators perform better at low angles of attack, while upstream actuators perform better at high angles of attack; the actuators positioned at the downward rolling side have a better effect than those positioned at the upward side. Furthermore, continuously variable control of the trim position can be achieved by changing the actuation voltage or modulation frequency, which provides a base for attitude manipulation by using active flow control instead of a mechanical control surface. Quantitative analysis of the flow field indicates that the leading-edge vortex on the upward side provides a rolling moment, while the recirculation zone on the downward side also contributes to the wing rock. This is a dynamic process, causing the flying wing to balance at a nonzero mean roll angle. The synthetic jet positioned at the downward rolling side can transport high-momentum fluids to the near-wall region, thereby suppressing flow separation and reducing the size of the recirculation zone. This enhances the lift on the control side and thus reduces the mean roll angle of the wing rock.

Deep reinforcement learning-based active flow control of vortex-induced vibration of a square cylinder

We mitigate vortex-induced vibrations of a square cylinder at a Reynolds number of 100 using deep reinforcement learning (DRL)-based active flow control (AFC). The proposed method exploits the powerful nonlinear and high-dimensional problem-solving capabilities of DRL, overcoming limitations of linear and model-based control approaches. Three positions of jet actuators including the front, the middle, and the back of the cylinder sides were tested. The DRL agent as a controller is able to optimize the velocity of the jets to minimize drag and lift coefficients and refine the control strategy. The results show that a significant reduction in vibration amplitude of 86%, 79%, and 96% is achieved for the three different positions of the jet actuators, respectively. The DRL-based AFC method is robust under various reduced velocities. This study successfully demonstrates the potential of DRL-based AFC method in mitigating flow-induced instabilities.

Numerical and experimental investigation of the in-phase and out-phase plasma actuation effects on the wake flow for Re = 1000

The aim is to characterize the role of symmetry pattern on the flow control induced by dielectric barrier discharge plasma actuators. Two DBD actuators are employed for in-phase excitation with duty cycle 50% leading to symmetric wake pattern and out-phase excitation for two pulsing frequencies St=0.2 and St=1 at Re=1000 which forms quasi-symmetric and asymmetric flow structures respectively. The modes deduced from POD and DMD methods represent the competition between symmetric (S) and asymmetric mode (K) in all cases. The harmonic in-phase plasma actuation with 50% duty cycle is the most effective flow control method with lowest power consumption. The harmonic out-phase excitation is not much effective; however adjustment of the actuator position can form the symmetric pattern with minimum power consumption. The superharmonic out-phase plasma actuation reduces the wake region however is not effective in lift reduction significantly and consumes high amount of energy. This indicates that phase difference and plasma location influence on the size and symmetry of the vortical structure. Then, based on the symmetry properties of the designed wake pattern created by frequency and phase difference of the plasma actuator, the effective active flow control can be performed. The numerical results are validated with experiments.

Multi-objective optimization of actuators and consensus ADP-based vibration control for the large flexible space structures

In this study, the multi-objective optimization and decision-making for optimal positions of actuators and consensus adaptive dynamic programming (CADP) are investigated to mitigate the vibration of large flexible space structures (LFSS). The optimization of the actuator positions maintains a balance between maximizing actuation efficiency and maximizing input voltage decoupling. Meanwhile, the CADP control method accelerates the attenuation of vibration when agents collaborate in the designed communication topology network. First, the electromechanical coupled dynamic model of the LFSS is built by the finite element method. Subsequently, the multi-objective optimization criteria are proposed, which maximize the actuation efficiency and decoupling of control inputs. Moreover, the multi-objective optimization and decision-making, which is based on the non-dominated sorting differential evolutionary algorithm (NSDE) and technique for order preference by similarity to ideal solution (TOPSIS), respectively, are performed to rapidly find the optimal position of actuators. In addition, the CADP control algorithm is designed and its stability is proven. Finally, for harmonic excitation under multi-frequency superposition, simulation comparisons based on the CADP and adaptive dynamic programming (ADP) are performed. Simulation results verify the effectiveness of the proposed optimization criterion of actuators and the CADP algorithm for vibration mitigation of LFSS.

Optimised Voltage Distribution on Piezoelectric Actuators for Modal Excitations Damping in Tapered Beams

Vibration mitigation is a prominent matter in several engineering fields. Several adverse phenomena are related to vibrations, such as fatigue, noise, etc. The availability of smart materials increases the solutions for both vibration damping and energy harvesting applications. Piezoelectric materials seem to be the most promising for these applications. However, their positioning significantly affects their efficiency. Several studies were performed on the positioning of piezoelectric actuators to dampen a target resonance in cantilever beams with constant cross-sections. Here, an analytical model for the optimal voltage distribution on an array of piezoceramic (PZT) actuator pairs is proposed in the case of tapered beams. The effect of tapering on the optimal voltage distribution was investigated for several eigenmode excitations and tapering ratios. The model outcomes were corroborated via FEM simulations and a fair agreement was found for each considered case.

Motorized Robotic Closed Cervical Traction: Biomechanical Proof of Concept.

Biomechanical study. To demonstrate that robotic cervical traction can apply closed cervical traction as effectively as manual weight-and-pulley traction in extension spring and cadaveric models. Closed cervical traction is used to reduce subaxial cervical spine dislocation injuries and to distract the intervertebral space during cervical spine surgery. Weight-and-pulley cervical traction relies on cumbersome and imprecise technology without any safeguard to prevent over-traction or weights being pulled/released inadvertently. A prototype robotic traction device was designed and manufactured by the authors with real-time tensile force measurement, ±1-lbs (5 N) force application accuracy, locking/non-backdriveable linear actuators with actuator position sensing, 200-lbs (900 N) maximum force capability, up to 20° of flexion/extension manipulation, <25-lbs (111 N) device weight, and compatibility with Gardner-Wells tongs or Mayfield head clamp. The device was tested using an extension spring model and an intact fresh cadaver specimen to assess applied and desired force over time and radiographic changes in the cervical spine as traction force increased. The cadaver was tested in manual traction initially and then robotic traction in 10-lbs (50 N) increments up to 80-lbs (355 N) to compare methods. The prototype device met or exceeded all requirements. In extension spring testing, the device reached the prescribed forces of both 25-lbs (111 N) and 80-lbs (355 N) accurately and maintained the desired weight. In cadaveric testing, radiographic outcomes were equivalent between the prototype and manual weight-and-pulley traction at 80-lbs (355 N; disk space measurements within ±10% for all levels), and the device reached the desired weight within±1-lbs (5 N) of accuracy at each weight interval. This preliminary work demonstrates that motorized robotic cervical traction can safely and effectively apply controlled traction forces.

A triple compound pendulum model to analyse the effect of an ankle-foot orthosis on swing phase kinematics.

Powered ankle-foot orthoses can be utilised to overcome gait abnormalities such as foot drop; however, normal gait is rarely restored with compensatory gait patterns arising and prevalence of gait asymmetry. Therefore, this study aims to determine the effect of orthosis mass and mass distribution on the swing phase of gait, to understand residual gait asymmetry with orthosis use. Using a triple compound pendulum model, which accounts for mass distribution of the limb and orthosis, the swing phase of gait is simulated in terms of natural dynamics and the effect of an orthosis on kinematic parameters is quantitatively determined. It was found that additional mass causes faster and shorter steps on the affected side due to rapid knee extension and reduced hip flexion, with particular actuator positions and natural cadence causing varying severity of these effects. Our study suggests that this model could be used as a preliminary design tool to identify subject specific optimum orthosis mass distribution of a powered ankle-foot orthosis, without the need for motion data or experimental trials. This optimisation intends to more accurately mimic natural swing phase kinematics, consequently allowing for the reduction in severity of gait asymmetry and the potential to improve rehabilitative outcomes.

Semiglobal Leader-Following Output Consensus of Discrete-Time Heterogeneous Linear Systems Subject to Actuator Position and Rate Saturation

Motivated by the fact that physical systems are usually subject to actuator position and rate saturation, we consider in this article the semiglobal leader-following output consensus problem of a group of discrete-time heterogeneous linear systems with position and rate-limited actuators by output feedback control law. Distributed observers are designed for followers to estimate the state of the leader and the follower itself, based on which a novel distributed control law is proposed. We show that, via the low gain feedback design technique and output regulation theory, the semiglobal leader-following output consensus of discrete-time heterogeneous linear systems can be achieved by the consensus protocol if each follower is reachable from the leader in a directed communication topology.

Optimal Design and Experimental Validation of a Cable-Driven Parallel Robot for Movement Training of the Head–Neck Joint

The optimal design and the experimental validation of a cable-driven parallel robot is discussed in this paper. This novel device is intended for assisting therapists in the rehabilitation of the head–neck joint. First, the motion of the head–neck joint was recorded by means of a Qualisys motion-capture system. The collected data was then analyzed in order to obtain the range of motion of the head and to identify some prescribed trajectories. A novel end-effector design was proposed to reduce the degrees of freedom needed to perform the desired head motion. The best design was found through an optimization problem where the cable tensions are minimized and the robot dexterity is maximized within its workspace. The objective of this optimization was to find the optimal actuator positions while satisfying a set of constraints. A prototype was proposed and experimental tests were conducted to validate the robot performance. In particular, a comparison between the actual trajectories and the desired ones was performed. The experimental test showed promising results.

Effects of powered ankle–foot orthoses mass distribution on lower limb muscle forces—a simulation study

This simulation study aimed to explore the effects of mass and mass distribution of powered ankle–foot orthoses, on net joint moments and individual muscle forces throughout the lower limb. Using OpenSim inverse kinematics, dynamics, and static optimization tools, the gait cycles of ten subjects were analyzed. The biomechanical models of these subjects were appended with ideal powered ankle–foot orthoses of different masses and actuator positions, as to determine the effect that these design factors had on the subject’s kinetics during normal walking. It was found that when the mass of the device was distributed more distally and posteriorly on the leg, both the net joint moments and overall lower limb muscle forces were more negatively impacted. However, individual muscle forces were found to have varying results which were attributed to the flow-on effect of the orthosis, the antagonistic pairing of muscles, and how the activity of individual muscles affect each other. It was found that mass and mass distribution of powered ankle–foot orthoses could be optimized as to more accurately mimic natural kinetics, reducing net joint moments and overall muscle forces of the lower limb, and must consider individual muscles as to reduce potentially detrimental muscle fatigue or muscular disuse.Graphical OpenSim modelling method to explore the effect of mass and mass distribution on muscle forces and joint moments, showing potential mass positioning and the effects of these positions, mass, and actuation on the muscle force integral.

Plasma Actuation for the Turbulent Mixing of Fuel Droplets and Oxidant Air in an Aerospace Combustor

In order to explore plasma-assisted turbulent mixing in aerospace engines, the dielectric barrier discharge plasma actuation for the turbulent mixing of fuel droplets and oxidant air in a ramjet combustor was studied using computational fluid dynamics. A two-way coupling of turbulent air and discrete droplets was realized by Eulerian–Lagrangian simulation, and the dielectric barrier discharge plasma action on flow was modeled by body force. The results show that the plasma actuation can rearrange the recirculation zone behind the evaporative V-groove flameholder, and the main mechanism of actuation is to increase the local momentum of the fluid; the actuation dimension, actuation intensity, and actuation position of the dielectric barrier discharge plasma have strong effects on the turbulent mixing of fuel droplets and oxidant air; and a relatively optimal turbulent mixing can be achieved by adjusting the actuation parameters.

Research on Sun-Oriented Spin-Stabilized Attitude Control of Micro/Nano Satellite Using Only Magnetic Control

Sun-oriented attitude control is one of the most important attitude control modes for most micro/nano satellites, which directly affects the on-orbit energy acquisition. Therefore, it is of great importance to use the simplest sensors and actuators and the most reliable algorithm to achieve sun-oriented attitude control. A sun-oriented spin-stabilized attitude control method for micro/nano satellites using only magnetic control is proposed in this paper, in which the control progress is divided into four phases: initial damping phase, sun-aligned phase, spin-up phase, and spin-stabilized phase. The influence of the shadow zone of the orbit, offset installation of sun sensor and solar panel, limitation of the field of view of the sun sensor, and environmental disturbance torques are all considered in the proposed method. The control performance is evaluated by numerical simulations, and the simulation results show that the proposed method is applicable to the satellite equipped with a sun sensor and a 3-axis magnetometer as attitude sensors and three magnetic torquers installed orthogonally as attitude actuators. The proposed method is applicable to most Earth-orbit satellites for which the geomagnetic field can provide sufficient attitude control torque.

Behavior of conducting polymer-based micro-actuators under a DC voltage

Conducting polymer-based micro-actuators are of great interest in soft MEMS as they exhibit large strains and forces in response to electrical stimulation. To date, these micro-actuators have very often been characterized by applying low frequency voltage to extract the electromechanical characteristics. However, many applications require maintaining the actuator’s position for several minutes. A micro-camera tracking the displacements of an object, the actuation of a cochlear implant during surgery, or closing micro-tweezers to manipulate objects are potential applications for which actuation is achieved by applying a direct current (DC) voltage. Knowledge of the behavior of micro-actuators under and after a DC voltage is crucial for modeling and future control. Consequently, the kinetics to reach the maximum strain followed by back-relaxation are identified. It is shown that it is the result of competition between an elastic restoring force and the backflow of the ions inside the actuator. A residual strain is observed after a short circuit and studied as a function of the DC voltage applied. It is demonstrated that the voltage and the chronology of the power-ups affect the actuator position and strain amplitude. The interpretation of the experimental results linked directly to the intrinsic operation of micro-actuators is presented.

Directional Force Feedback for a 3 DOF Pneumatic Haptic Finger

This paper presents the design, kinematic, and nonlinear control algorithm of a 3 degrees of freedom (DOF) pneumatic haptic finger developed for elastographic imaging virtual palpation. This haptic interface allows for precise tracking of the index finger position and can provide directional force perception at the fingertip. Of the 4 DOF of the human finger, two are kinematically coupled (distal and proximal interphalangeal joints), one DOF of the metacarpophalangeal (MCP) joint is controlled independently, while the remaining MCP joint DOF is only measured. Relationships between the joint angles and actuator positions, as well as fingertip to actuator forces are derived in closed form. A sliding mode nonlinear pneumatic controller is implemented and experimental results are presented.

Echo-state-network-based iterative learning control of distributed systems

The paper proposes an effective modeling and control procedure for the distributed-parameter systems using the echo-state network. The main idea is to reconstruct the spatiotemporal dynamics defined in a given multi-dimensional domain. In the investigated problem positions of both sensors and actuators are fixed allowing to delegate the complex system dynamics to echo-state network. Imposing a proper partitioning of the spatial domain, a specific topology of a neural network is used to form a reservoir capable to follow not only temporal but also spatial dynamics of the system. Based on available historical data, neural network model is initially trained and then used to derive the control law in the framework of iterative learning control. The echo-state network can be retrained after a particular control iterate in order to reduce model uncertainty and to fit it to the current operating conditions as much as possible. The performance of the proposed approach is tested and evaluated on the example of the squared clamped plate control.

FPGA-based Control Design and Implementation of DELTA robots Using Horizontal-Axial Pneumatic Actuators

This study researched, analyzed, and applied a field-programmable gate array (FPGA) to develop a control system for the DELTA robot with three pneumatic actuation subsystems. To achieve positioning accuracy, a dual-feedback control framework is first applied to control the position of a rodless pneumatic actuator. The inner pressure difference between the actuator and cylinder was used as feedback signals. Then, the derived dynamic model is included in the control strategy to conduct decoupling and system linearization on the nonlinear parallel manipulator using inverse dynamic control. Additionally, to realize the operation of the integrated control system under the FPGA environment, a multilayered neural network framework is designed to learn the inverse dynamic control behaviors. The motion control experiments involving single- and three-axis translational parallel manipulators revealed that the established FPGA-based control system exhibits high precision over the reachable workspace regarding the DELTA robot's three-dimensional trajectory tracking control.

Quantitative evaluation of properties of structural solutions of electrohydraulic positioning actuators

Based on the analysis of known electro-hydraulic positioning actuators, its generalized scheme was given, which includes: control unit, command formation unit for reaching given position, executive mechanism, position sensor, and hydraulic energy supply unit. It was determined that the main difference between the actuators lies in the command formation unit, the structural solutions of which are based on four control methods: analog control of fluid supply to reach preset position; discrete control the time of fluid supply to reach preset position; discrete control of fluid supply to reach preset fixed position; discrete control of portioned fluid supply to reach preset position. For various structural solutions of actuators, the influence of the main parameters on their effectiveness in achieving the basic properties was analysed. A quantitative evaluation was proposed, which made it possible to reveal the relationship between the structure and properties of the actuators. The obtained results can be used to develop new effective positional actuators.