Primary Actuator Research Articles

MEMS Micromirror Actuation Techniques: A Comprehensive Review of Trends, Innovations, and Future Prospects

Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation of these mirrors is critical in determining their performance, as it contributes to factors such as response time, scanning angle, and power consumption. This article aims to provide a thorough exploration of the actuation techniques used to drive micromirrors, describing the fundamental operating principles. The four primary actuation modalities—electrostatic, electrothermal, electromagnetic, and piezoelectric—are thoroughly investigated. Each type of actuator’s operational principles, key advantages, and their limitations are discussed. Additionally, the discussion extends to hybrid micromirror designs that combine two types of actuation in a single device. A total of 208 closely related papers indexed in Web of Science were reviewed. The findings indicate ongoing advancements in the field, particularly in terms of size, controllability, and field of view, making micromirrors ideal candidates for applications in medical imaging, display projections, and optical communication. With a comprehensive overview of micromirror actuation strategies, this manuscript serves as a compelling resource for researchers and engineers aiming to utilize the appropriate type of micromirror in the field of optical scanning technology.

Characterization and verification of the optimal feedback gain of a satellite magnetorquer-based attitude control system

In spacecraft mission planning and operation, the attitude determination and control subsystem (ADCS) of a satellite provides information about the orientation of the satellite in the inertial reference frame. Furthermore, this subsystem produces the control actions required to adjust the orientation of the satellite, especially in the low-Earth orbit (LEO) regime. This paper focuses on the satellite’s three-axis attitude control problem within the context of active and passive control, which includes detumbling control, pointing control, magnetic control, and attitude stabilization after solar panel wing deployment using magnetorquers as the primary actuators. The objective is to stabilize and reduce the angular rate while orienting the satellite to the desired attitude. The proposed satellite attitude control system (ACS) strategies are designed, developed, characterized, and verified. These strategies encompass the B-dot control algorithm for detumbling control along with pointing control and attitude stabilization after solar panel wing deployment. hardware-in-the-loop simulation (HiLs) tests are conducted to assess the performance of the satellite magnetorquer-based ACS in the presence of noise. These tests involve a relative Earth’s magnetic field (EMF) generator in conjunction with SGP-4-based satellite orbital propagator high-level control software. Additionally, cascade proportional-integral-derivative (PID) and state-dependent Riccati equation (SDRE) controllers are implemented to generate sufficient torque using three-axis magnetorquers on a frictionless air-bearing platform. The platform is balanced to closely simulate the dynamic motion of a spacecraft in space. The testing includes a single initial condition and three inertia conditions for stabilization after solar panel wing deployment. Finally, the effectiveness of the cosimulation as a primary experiment through an integrated HiLs process is validated. This comprehensive approach confirms the control system’s performance and its ability to meet mission requirements.

A high resolution and wide range valve for micronewton cold gas thrusters.

Numerous scientific satellites require micronewton thrusters for compensating environmental disturbances. The mass flow control proportional valve plays a crucial role in precisely regulating the thrust. To meet the high resolution and wide range requirements of the thrusters, this paper introduces a novel proportional valve with two sets of independently controllable piezoelectric stack. One set of the piezo-stack is used to compensate the stroke loss of the valve core, mainly caused by the deformation of the valve seat. The valve sealing mechanism is carefully analyzed to reduce the stroke loss. Another set of the stack works as the primary actuator, enabling the high mass flow control resolution. Two sets of independently controlled piezoelectric stacks not only expand the range and improve the range ratio but also provide redundancy and enhance reliability. This means that the actuator can still operate at lower ranges even if one piezo-stack is damaged. The piezo-actuators are assembled using U-shaped connectors, creating a compact and space-efficient overall design. Experimental tests have been conducted to verify the performance of the valve, which demonstrated a mass flow range of 0-675 μg/s with a resolution better than 0.1 μg/s and a flow noise below 0.1 μg/s/Hz1/2 at 0.1 mHz-1Hz.

Satellite actuator balancing based on the disturbance measurement table data

Reaction wheel is one of primary actuators for satellite attitude control. Since it uses electrical power supplied by the solar panels and thus consumes no invaluable fuel of satellite, it has been used as primary actuator. However, rotation of reaction wheel induces torque and force disturbances which degrade the satellite attitude stability quality. The disturbances are mainly due to static and dynamic imbalances of the wheel. These imbalances shall be reduced on the stage of manufacturing. In this his paper a method for the imbalance reduction of the wheel is suggested. Torque/force measurement table is used to measure the disturbances of the reaction wheel and the measured data are used for the identification of location and magnitude of the imbalances. The corrections of the imbalances are performed by adding proper counter masses on the wheel. Through iterative balancing steps, the static and dynamic imbalances are remarkably reduced.

Nonlinear PID-based temperature control techniques in greenhouses using natural ventilation

Greenhouses provide controlled environments for cultivating crops. This work explores the design of PID-based greenhouse climate control techniques using natural ventilation, considering both measurable disturbances and operational constraints. A nonlinear model was developed to relate natural ventilation (the primary climate actuator) with interior temperature in greenhouses, the critical factor being the relationship between air flow rate and vent aperture, which is a source of uncertainty in the related literature. Novel calibration issues are included for this term. The nonlinear model is used to devise control strategies combining PI control and feedback linearization. The resulting simulations and robustness analysis, which accounts for uncertainties in the relevant parameters, demonstrate that the combination of PID and feedback linearization techniques is a suitable control approach. In summary, practical tradeoffs can be achieved between setpoint tracking, disturbance rejection, control effort, and robustness.

A Low-Cost Microcontroller-Based Normal and Abnormal Conditions Classification Model for Induction Motors Using Self-Organizing Feature Maps (SOFM)

Digital twins have provided valuable information for making effective decisions to ensure high efficiency in the manufacturing process using virtual models. Consequently, AC electric motors play a pivotal role in this framework, commonly employed as the primary electric actuators within Industry 4.0. In addition, classification systems could be implemented to identify normal and abnormal operating conditions in electric machines. Moreover, the execution of such classification systems in low-cost digital embedded systems is crucial, enabling continuous monitoring of AC electric machines. Self-Organized Maps (SOMs) offer a promising solution for implementing classification systems in low-cost embedded systems due to their ability to reduce system dimensionality and visually represent the model’s features, so local digital systems can be used as classification systems. Therefore, this paper aims to investigate the utilization of SOMs for classifying operating conditions in AC electric machines. Furthermore, when integrated into an embedded system, SOMs detect abnormal conditions in AC electric machines. A trained SOM is deployed on a C2000 microcontroller to exemplify the proposed approach. It should be noted that the proposed structure can be adapted for implementation with different systems in the context of Industry 4.0.

2D Arrays of Soft Actuators Performing Out‐of‐Plane Local Inflation for Shape Displays

Elementary actuators performing branching or surface swelling are the primary units in the actuator integration system that is leveraged in works requiring a high versatility and complex motion. However, those primary actuator units often lack scalability or compatibility at assembly into a compact form due to the complexity of the structure and the actuation interference between adjacent units. Herein, it is shown that the phase‐change actuator in a simple bilayer structure of a top active layer and a bottom constraint layer achieves 1D surface swelling, such that the closely packed 2D array system of this actuator is easily constructed. Upon resistive heating, the active layer inflates based on the phase change of microliquid droplets embedded in an elastomer body. The inflation along the lateral direction of the actuator is suppressed by controlling the thickness ratio between the active and the constraint layers. The actuation of individual units in the array system is performed independently using a switching device with a microcontroller for the parallel application of resistive heating. The application of 2D shape morphing of the actuator arrays in beam steering and shape displays is investigated.

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.

Design and Preliminary Performance Assessment of a PHM System for Electromechanical Flight Control Actuators

The evolution toward “more electric” aircraft has seen a decisive push in the last decade due to growing environmental concerns and the development of new market segments (flying taxis). Such a push has involved both the propulsion components and the aircraft systems, with the latter seeing a progressive trend in replacing traditional solutions based on hydraulic power with electrical or electromechanical devices. Flight Control Systems (FCSs) are one of the aircraft systems affected the most since the adoption of Electromechanical Actuators (EMAs) would provide several advantages over traditional electrohydraulic or mechanical solutions, but their application is still limited due to their sensitivity to certain single points of failure that can lead to mechanical jams. The development of an effective and reliable Prognostics and Health Management (PHM) system for EMAs could help in mitigating the risk of a sudden critical failure by properly recognizing and tracking the ongoing fault and anticipating its evolution, thus boosting the acceptance of EMAs as the primary flight-control actuators in commercial aircraft. The paper is focused on the results of the preliminary activities performed within the CleanSky 2/Astib research program, dedicated to the definition of the iron bird of a new regional-transport aircraft able to provide some prognostic capabilities and act as a technological demonstrator for new PHM strategies for EMAs employed in-flight control systems. The paper is organized as follows. At first, a proper introduction to the research program is provided, along with a brief description of the employed approach. Hence the simulation models adopted for the study are presented and used to build synthetic databases to inform the definition of the PHM algorithm. The prognostic framework is then presented, and a preliminary assessment of its expected performance is discussed.

A Compact Electromagnetic Dual Actuation Positioning System with a 10 mm Range and Nanometer Resolution

In this manuscript, a compact electromagnetic dual actuation positioning system (CEDAPS) based on the Lorentz force principle that features a 10 mm range and nanometer-scale resolution with flexure guides is presented. Firstly, the stiffness of the flexure mechanism is modelled. Secondly, based on it, the primary coil is designed, and from its performance, a suitable secondary coil is made to compensate for the deficiency of the primary actuation subsystem. The characteristics of the forces generated by these coils are also evaluated by an electromagnetic FEA simulation. Thirdly, a control scheme is presented that combines the performances of these two actuators, and finally, a prototype is fabricated to evaluate the performance. The results show a 10 nm resolution for a 10 mm (±5 mm) stroke with low sub-micron sinusoidal tracking errors and nanometer accuracy for step tracking under the proposed control scheme. The thermal properties of the system are also presented.

A Novel Approach for Active Surge Control in Multistage Centrifugal Compressor

Compressors are used in the hydrocarbon industry from upstream to downstream to boost the pressure required to transport gas into processing and transportation pipelines inside and toward processing facilities. Turbo-centrifugal compressors are subject to repetitive damages resulting from the manifestation phenomenon known as surge, observed as fluid flow reversal at low mass flows. Active surge control aims to increase the compressor operating region by allowing the compressor to operate at low mass flow in the naturally-unstable region of the compressor. Surge is avoided in the industry by forcing the operating point to the stable region of the compressor curve. Active surge control aims to control the surge phenomenon by extending the stable operating region. This work developed a novel model-based control approach for effective compression system active surge control on an automatic coupled recycle valve as a primary actuator. The feedback linearization technique is used to reduce the system complexity by providing a linear representation of the highly nonlinear system. A detailed description of the feedback linearization method for centrifugal compressors and a dual controller design was developed in this paper.

Mixed-Integer MPC Strategies for Fueling and Density Control in Fusion Tokamaks

Model predictive control (MPC) is promising for fueling and core density feedback control in nuclear fusion tokamaks, where the primary actuators, frozen hydrogen fuel pellets fired into the plasma, are discrete. Previous density feedback control approaches have only approximated pellet injection as a continuous input due to the complexity that it introduces. In this letter, we model plasma density and pellet injection as a hybrid system and propose two MPC strategies for density control: mixed-integer (MI) MPC using a conventional mixed-integer programming (MIP) solver and MPC utilizing our novel modification of the penalty term homotopy (PTH) algorithm. By relaxing the integer requirements, the PTH algorithm transforms the MIP problem into a series of continuous optimization problems, reducing computational complexity. Our novel modification to the PTH algorithm ensures that it can handle path constraints, making it viable for constrained hybrid MPC in general. Both strategies perform well with regards to reference tracking without violating path constraints and satisfy the computation time limit for real-time control of the pellet injection system. However, the computation time of the PTH-based MPC strategy consistently outpaces the conventional MI-MPC strategy.

A Constrained Control Allocation and Tuning Scheme for Hybrid Actuators in Spacecraft Attitude Control

Agile rotational maneuvers of spacecraft requires careful execution since its actuators may not be able to produce the demanded torques, causing the state trajectories to deviate and a desired attitude would not be guaranteed. We investigate the control allocation problem for a redundant set of hybrid actuators that include reaction wheels, magnetorquers, and continuous-force thrusters. The main objective of the magnetorquers is to dump momentum from the reaction wheels, whereas the wheels are the primary actuators in attitude control, and more agile maneuvers or faster unloading of momentum can be handled by the thrusters. A modified mixed optimization scheme for control allocation is presented where the equality constraints account for satisfying the high-level (virtual) control inputs for both attitude control and momentum dumping. Variants of dynamic weights in the optimization are developed such that magnetorquers and thrusters may contribute with a relative degree of importance in the attitude control problem. The control allocation scheme is solved using quadratic programming where simulation results are shown for fast and slow rotational maneuvers together with fast and slow momentum dumping.

Ion‐selectivity of polypyrrole carbide‐derived carbon films in aqueous electrolytes

AbstractIn this work, we have combined polypyrrole (PPy) doped with dodecylbenzene sulfonate (DBS−) and carbide‐derived carbon (CDC), forming PPyCDC (PPy/DBS‐CDC) composites. Scanning electron microscopy revealed for PPyCDC that most CDC particles are located on the surface of the films. This work's main goal is to investigate the ion‐selectivity of the novel PPyCDC composite by linear actuation studies, with primary actuation taking place at discharging. Four different aqueous electrolytes are applied with hydrophobic cations, such as TMA+ (tetramethylammonium ion) and EDMI+ (1‐ethyl‐2,3‐dimethyl imidazolium ion). They are hydrophilic with Li+ (lithium‐ion) and Na+ (sodium ion). It was possible to distinguish each cation from linear actuation studies, either cyclic voltammetry or square wave potential steps. In the case of pristine PPy/DBS, that ion differentiation could not separate. Chronopotentiometric measurements of both films (PPyCDC and PPy/DBS) were performed. It could control (read) the strain for PPyCDC films and the potential at constant current density. The electrical energy adapts to exchange cations, forming a sensor device with ion‐selectivity of the applied cations considering their hydrophilic and hydrophobic characteristics. The best specific capacitance (energy storage) is found for EDMI+ cations in PPyCDC films with 193 F g−1, enabling this composite in multifunctional applications.

A novel dual-stage shape memory alloy actuated gripper

PurposeThe paper aims to propose a novel dual-stage shape memory alloy (SMA) actuated gripper (DAG), of which the grasp performance is improved through primary and secondary actuation.Design/methodology/approachThis paper presents a method of integrating the design of dual-stage actuation modules based on the SMA bias actuation principle to enhance the grasping shape adaptability and force modulation of a DAG. The actuation angle range and grasping performance of the DAG are investigated by thermomechanical analysis and the finite element method based numerical simulation.FindingsThe results of present experiments and simulations indicate that the actuation angle scope of the DAG is about 20° under no load, which enables the grasping space occupied by an object in the DAG from 60 mm to 120 mm. The grasping force adjusted by changing the input power of the primary main actuation module and secondary fine-tuning actuation module can reach a maximum of 2 N, which is capable of grasping objects of various sizes, weights, shapes, etc.Originality/valueThe contribution of this paper is to design a DAG based on SMA, and establish the solution methods for the primary main actuation module and secondary fine-tuning actuation module, respectively. It lays a foundation for the research of lightweight and intelligent robotic grippers.

Experimental Study on the Closed-Loop Control of a Soft Ring-Shaped Actuator for Gastric Simulator

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In-vitro</i> gastric simulators are soft robotic systems that reproduce the change of the food or drug by emulating the stomach's motility functions. The control of gastric simulators traditionally lies in tuning the actuators via open-loop approaches. However, the lack of precise position control, external disturbances, sensitivity to model uncertainties, and continues retuning are solid motivations for employing closed-loop methods to control gastric simulators. A bellows-driven viscoelastic soft ring-shaped pneumatic actuator (RiSPA), including five spring-like bellows, was developed for stomach simulators’ primary actuation system. This article studies the implementation of closed-loop methods equipped with the online feedback system on the RiSPA for the first time. All technical aspects for implementing the closed-loop control and the sensor-actuator integration are discussed in detail. A model-based closed-loop method has been implemented and compared with a classic model-free method to show the closed-loop system's ability to reject model uncertainties. The experimental results in both the tracking trajectory and the regulation performances are thoroughly compared to the open-loop approach, where the superiority of closed-loop techniques is demonstrated. A mechanical setup is designed to show the ability of the closed-loop approach in dealing with the disturbances and external loads as well.

Energy-aware redundant actuation for safe spring-assisted modular and reconfigurable robot

AbstractA spring-assisted modular and reconfigurable robot (SA-MRR) has been recently developed at our laboratory to reinforce its performance and enable safe and dexterous operation in human–robot environments. Multiple working mode (MWM) control enables each SA-MRR joint module to switch independently between working in a primary actuation mode and a secondary, spring-assisted mode that may improve task-specific energy performance measures and safety in a variety of manipulation tasks. The spring-assisted mode is characterized by synergy of spring and motor energy and may be summoned to offset motor energy demands or to safeguard a reconfigurable set of secondary joint limits. In this research work, two spring-assisted working mode strategies are proposed, and their characteristics have been investigated for SA-MRR actuation energy advantages while safe robot segregation in collaboration tasks is maintained. One MWM strategy has been designed to safeguard task-specific joint limits and is able to decrease motor energy consumption in some tasks. Another MWM strategy has been designed for energy efficiency and was able to reduce motor energy per cycle by $ \text{72}$ % in a simulated manipulation task while maintaining spatial safety constraints. Numerical simulations have demonstrated the effectiveness of the proposed spring-assisted working mode strategies for energy-aware safe manipulation applications.

ЗАСТОСУВАННЯ КОМБІНОВАНОЇ СХЕМИ ОДНОФАЗНОГО ВКЛЮЧЕННЯ АСИНХРОННОГО ДВИГУНА ЯК ЗАСІБ ПІДВИЩЕННЯ ЕНЕРГОЕФЕКТИВНОСТІ ГІДРОПРИВОДУ ПОСТУПАЛЬНОГО РУХУ

The peculiarities of the modes of operation of the hydraulic drive of translational motion with throttle speed control, in which the asynchronous motor with single-phase power supply is used as the primary actuator. A combined circuit of such an actuator with a phase-shifting capacitor is proposed, which allows to increase its energy efficiency in the forward and reverse modes of the hydraulic rod when changing the degree of opening of the hydraulic control valve by switching power circuits and using voltage regulation. References 10, figures 6, table 1.

Design and test of a compact large-stroke dual-drive linear-motion system

This paper presents the design, modelling, analysis, and test of a piezo-actuated dual-drive linear motion system, capable of millimeter stroke with nanometer resolution. The primary actuator is a two-stage bridge-type amplifier with hybrid flexure hinges, which is driven by a piezo-stack actuator and generates output stroke greater than 6 mm. The micro actuation is directly driven by an extra piezo-stack to achieve resolution of 20 nm. A very large amplification ratio of 91 is achieved, which implies not only large stroke but also compactness. An inherent characteristic for the multi-stage compliant displacement amplifier, ‘kick-back’ phenomenon, is first analyzed and eliminated by using the stiffness distribution method. The architectural parameters are optimized by genetic algorithm to find the trade-off among natural frequency, stroke and stiffness ratio. The optimized design was then fabricated and tested. The superiority of the proposed system is remarkable compared with other similar works. The concept and approach outlined are generic and can be extended to this class of actuators.

A novel model-based metaheuristic method for prognostics of aerospace electromechanical actuators equipped with PMSM

The prior knowledge of incipient failures of primary flight command electromechanical actuators (EMAs) with prognostic algorithms can be very beneficial. Indeed, early and proper detection and interpretation of the deterioration pattern can warn for replacing the servomechanism before the actual manifestation of the abnormal behaviour. Furthermore, such algorithms often exploit a model-based approach established on the direct comparison between the actual (High Fidelity) and the monitor (Low Fidelity) systems to identify fault parameters through optimization processes. The monitor model allows the acquisition of accurate and precise results with a contained computational effort. The authors developed a new simplified monitor model capable of faithfully reproducing the dynamic response of a typical aerospace EMA equipped with a Permanent Magnet Sinusoidal Motor (PMSM). This digital twin senses mechanical and electrical faults: friction, backlash, coil short circuit, static rotor eccentricity, and proportional gain. Fault detection and identification task are performed by comparing the output signal of the reference system (real or simulated) with the one obtained from the monitor model. After that, the Genetic Algorithm is chosen as the optimization algorithm to match the two signals by iteratively changing the fault parameters to detect the global minimum of a quadratic error function. Once a suitable fit is obtained, the corresponding optimization parameters are correlated with the considered progressive failures to evaluate the system’s health status. The high-fidelity reference models analysed in this work have been previously conceived, developed, implemented in Matlab-Simulink, and validated experimentally by researchers of the ASTRA group of the DIMEAS of Politecnico di Torino.