Onboard Actuators Research Articles

Hardware-In-the-Loop Evaluation of a Robust C⁎ Control Law on MuPAL-α Research Aircraft

This article presents the design and evaluation of a robust C⁎ control law through Hardware-In-the-Loop Simulation (HILS) of JAXA’s research aircraft called Multi-Purpose Aviation Laboratory (MuPAL-α). The C⁎ control law, which is a widely used flight control architecture in aviation industries, is designed using structured H∞ synthesis. This design method provides robustness of the controller for flight condition changes and uncertainties associated with the dynamics of MuPAL-α. HILS tests allow on-ground evaluation of controllers using actual actuators. The HILS results show that the designed controller adequately tracks pilot commands in the presence of airspeed variation, uncertainties in the modeling of the onboard actuators, and wind gust.

Statistics-Based Automated Control for a Swarm of Paramagnetic Nanoparticles in 2-D Space

Swarm control is one of the primary challenges in microrobotics. For the automated control of such a microrobotic system with small size and large population, conventional methods using precise robot models and robot–robot communications lose effectiveness due to the complex locomotion of micro/nano agents in a swarm and difficult implementation of onboard actuators and sensors for individual motion control and motion feedback. This article proposes a statistics-based approach and reports the fully automated control of a swarm of paramagnetic nanoparticles including the swarm pattern formation, identification, tracking, motion control, and real-time distribution monitoring/control. By establishing the swarm statistics, collective behaviors of a nanoparticle swarm can be quantitatively analyzed by computers. Algorithms are designed based on the statistics to automatically generate and identify the vortex-like paramagnetic nanoparticle swarm (VPNS), which present robustness to the dose and initial distribution of the nanoparticle swarm. In order to robustly track a VPNS, a statistics-based tracking method is proposed, in which 500 boundary points of the VPNS are extracted and the VPNS distribution is optimally recognized. And, with the proposed gathering improvement control, experiments show that over 70% nanoparticles can be gathered in the VPNS. Furthermore, an automated motion control scheme for the VPNS is proposed which shows high-accuracy trajectory tracking performance (tracking error: <5% body length). Besides, real-time monitoring of the distribution region/density and control of the distribution area for a nanoparticle swarm are also realized by using the statistics. Experimental results validate the feasibility of the proposed method in automated control of paramagnetic nanoparticle swarms.

Optimization Techniques for Prognostics of On-Board Electromechanical Servomechanisms Affected by Progressive Faults

In relatively recent years, electromechanical actuators have gradually replaced systems based on hydraulic power for flight control applications. Electromechanical servosystems are typically operated by electrical machines that transfer rotational power to the controlled elements (e.g. the aerodynamic control surfaces) by means of gearings and mechanical transmission. Compared to electrohydraulic systems, electromechanical actuators offer several advantages, such as reduced weight, simplified maintenance and complete elimination of contaminant, flammable or polluting hydraulic fluids. On-board actuators are often safety critical; then, the practice of monitoring and analyzing the system response through electrical acquisitions, with the aim of estimating fault evolution, has gradually become an essential task of the system engineering. For this purpose, a new discipline, called Prognostics, has been developed in recent years. Its aim is to study methodologies and algorithms capable of identifying such failures and foresee the moment when a particular component loses functionality and is no longer able to meet the desired performance. In this paper, authors have introduced the use of optimization techniques in prognostic methods (e.g. model-based parametric estimation algorithms) and have proposed a new model-based fault detection and identification method, based on Genetic Algorithms optimization approach, able to perform an early identification of the aforesaid progressive failures, investigating its ability to identify timely symptoms alerting that a component is degrading.

Microrobotics and Microorganisms: Biohybrid Autonomous Cellular Robots

Biohybrid microrobots, composed of a living organism integrated with an artificial carrier, offer great advantages for the miniaturization of devices with onboard actuation, sensing, and control functionalities and can perform multiple tasks, including manipulation, cargo delivery, and targeting, at nano- and microscales. Over the past decade, various microorganisms and artificial carriers have been integrated to develop unique biohybrid microrobots that can swim or crawl inside the body, in order to overcome the challenges encountered by the current cargo delivery systems. Here, we first focus on the locomotion mechanisms of microorganisms at the microscale, crucial criteria for the selection of biohybrid microrobot components, and the integration of the selected artificial and biological components using various physical and chemical techniques. We then critically review biohybrid microrobots that have been designed and used to perform specific tasks in vivo. Finally, we discuss key challenges, including fabrication efficiency, swarm manipulation, in vivo imaging, and immunogenicity, that should be overcome before biohybrid microrobots transition to clinical use.

C-Balls: A Modular Soft Robot Connected and Driven via Magnet Forced

This paper describes a cellular robot(C-Balls) consisting of soft spherical modules with on-board actuation, power, computation and wireless control system. The robot modules maintain connection and realize relative movement by utilizing magnetic force and friction force between driving units inside the soft modules. Preliminary tests of locomotion and deformation of the robot are proposed. The rolling experiment displays the mobility of the robot of two spherical modules. The deforming experiments indicate that the robot with five spherical modules deforms from linear to circular configuration successfully. Further more, a climbing experiment is conducted, which shows the robot can climb on various surfaces including soft materials.

Three-Dimensional Manipulation of a Spherical Object Using Ultrasound Plane Waves

In this letter, we demonstrate a new robotic framework where a lightweight balloon with no onboard actuators or batteries acts as a mid-air robot that travels three-dimensionally within a workspace. The workspace contains five sparsely arranged ultrasound transducer arrays emitting steerable plane waves that cause acoustic radiation forces on the balloon and actuate it. The fabricated system performs a dynamic PID control of the movement of the balloon based on visual feedback. For practical operation of the system, we experimentally modeled the acoustic radiation force applied on a sphere. Based on the model, we developed the system dynamics model and a control law. We constructed a prototype system and demonstrated meter-scale three-dimensional manipulation of a 200 mm-diameter spherical object. Our proposed methodology is beneficial for long-term mid-air robotic applications, such as 24-h indoor surveillance system with no blind spots caused by battery limitation.

Proposal of a new simplified fluid dynamic model for aerospace servovalves

Highly detailed computer models are required for design and development of modern flight control systems, capable of emulating with high accuracy the behaviour of on-board equipment. At the same time, different simplified models are needed, specifically intended for operations such as the optimization of preliminary design and the development of diagnostic or prognostic strategies. These simplified models are required to combine sufficient levels of accuracy and reliability with reduced computational costs, to minimize the computational burden associated with prognostic and optimization algorithms. In this work, we focus on electro-hydraulic actuators, since they are critical subsystems in terms of safety and availability of the aircraft. Advanced monitoring and prognostic algorithms require new numerical models, combining an acceptable computational effort with a satisfying ability to simulate their performance and dynamics. To this purpose, this paper proposes a new simplified numerical model of the servovalve fluid-dynamic behaviour. This numerical algorithm, based on a very compact semi-empirical formulation, is intended to take into account in a simplified but sufficiently accurate way several typical effects related to the SV spool geometry and the operating conditions. To evaluate the approximations introduced by this model into a system-level simulation, it has been integrated into a dedicated numerical model simulating a simple electrohydraulic on-board actuator, and compared with a higher fidelity servovalve model.

Fully Soft 3D-Printed Electroactive Fluidic Valve for Soft Hydraulic Robots.

Soft robots are designed to utilize their compliance and contortionistic abilities to both interact safely with their environment and move through it in ways a rigid robot cannot. To more completely achieve this, the robot should be made of as many soft components as possible. Here we present a completely soft hydraulic control valve consisting of a 3D-printed photopolymer body with electrorheological (ER) fluid as a working fluid and gallium-indium-tin liquid metal alloy as electrodes. This soft 3D-printed ER valve weighs less than 10 g and allows for onboard actuation control, furthering the goal of an entirely soft controllable robot. The soft ER valve pressure-holding capabilities were tested under unstrained conditions, cyclic valve activation, and the strained conditions of bending, twisting, stretching, and indentation. It was found that the max holding pressure of the valve when 5 kV was applied across the electrodes was 264 kPa, and that the holding pressure deviated less than 15% from the unstrained max holding pressure under all strain conditions except for indentation, which had a 60% max pressure increase. In addition, a soft octopus-like robot was designed, 3D printed, and assembled, and a soft ER valve was used to stop the fluid flow, build pressure in the robot, and actuate six tentacle-like soft bending actuators.

New prognostic neural method by discrete wavelet transforms for electromechanical flight controls affected by progressive faults

Progressive failures affecting onboard electromechanical actuators (EMA), especially if related to primary flight commands, could be a critical issue for the aircraft reliability and, in the worst cases, could compromise its safety. In the last years strong interest is expected by the development of prognostic algorithms able to provide an early identification of the precursors of EMA progressive failures. In this work authors proposes a new prognostic method based on two artificial neural networks (ANN), a basic and an enhanced feedforward neural network, performing the fault detection and identification of two critical progressive faults often affecting the EMA brushless motor (i.e. turn-to-turn short circuit of a stator coil and rotor static eccentricity); in order to identify a suitable data set able to guarantee an affordable ANN classification, the said failures precursors are properly pre-processed by a Discrete Wavelet Transform, extracting several features used as input of the proposed prognostic algorithm.

An All-Electric-Aircraft Tailored SiC-Based Power Factor Correction Converter with Adaptive DC-Link Regulator

In recent years the aerospace industry has made a growing effort to develop a quieter and more environmentally friendly aircraft. In particular, several research activities have been focused on innovative solutions aimed at the design/optimization of an on-board electric system fully compatible with this new approach. A first important step in the evolution towards an All Electric Aircraft (AEA) is the replacement of the hydraulic actuators with fully electric ones. The transition process is not easy to carry out, since weight, size and reliability represent highly critical issues for aircraft applications. In this context, the significant improvements in semiconductor technologies can be exploited as a critical means to overcome the constraints mentioned. Indeed, this work proposes a Silicon Carbide (SiC) based Power Factor Correction (PFC) converter, whose design and control have been tailored in order to properly supply a wide range of on-board Electro-Mechanical Actuators (EMA). In particular, while the adopted circuit topology allows for power factor correction and bi-directional power flow, the SiC technology, thanks to the higher efficiency with respect to other semiconductor-based technologies, leads to a significant reduction in the overall system weight/volume. Furthermore, to meet the strict requirements in terms of dynamic and steady state performance imposed by the application, a novel adaptive regulator is conceived. A reduced-scale laboratory prototype of the SiC-based converter (3 kVA) is realized in order to verify the effectiveness of the proposed design and control approach.

Multistress Characterization of Fault Mechanisms in Aerospace Electric Actuators

The concept behind the more electric aircraft is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical, and bleed air/pneumatic systems, and pursue efficiency, reliability, and maintainability. This paper presents a specialized test rig whose main objective is to assess insulation lifespan modeling under various stress conditions, especially investigating the interaction between ageing factors. The test setup is able to reproduce a multitude of environmental and operational conditions at which electric drives and motors, used in aerospace applications, are subjected. It is thus possible to tailor the test cycle in order to mimic the working cycle of an electrical motor during real operation in aircraft application. The developed test-rig is aimed at projecting the technology readiness to higher levels of maturity in the context of electrical motors and drives for aerospace applications. Its other objective is to validate and support the development of a comprehensive insulation degradation model.

Decentralized Active Control of Multistory Civil Structure with Wireless Smart Sensor Nodes

AbstractWireless smart sensors, a popular option for structural health monitoring, are an exciting alternative to traditional tethered systems for structural control. Their onboard communication, sensing, actuation, and processing capabilities offer all the components for feedback control to limit structural response during earthquakes and wind. However, wireless smart sensors pose unique challenges for structural control including communication latency, delays, and data loss. Previous research in wireless structural control has used decentralized control approaches to overcome these inherent limitations. However, these experimental investigations have focused on semiactive control systems, in which stability is guaranteed. Thus, the semiactive wireless control implementations are less sensitive to delays and sampling rate limitations imposed by the smart sensors. This paper presents an experimental investigation of decentralized wireless active control. All the elements of the wireless control system are...

A Novel 4-DOF Origami Grasper With an SMA-Actuation System for Minimally Invasive Surgery

Minimally invasive surgery (MIS) is one of the most challenging techniques for robot designers due to the limited size of access points, the high miniaturization level, and the dexterity needed for performing surgical tasks. Conversely, only a few microfabrication technologies are currently available for developing such small-sized systems, which allow safe operations in human bodies. In order to match these challenges in MIS, both design and integration of actuation systems should proceed in parallel with an identification of most effective transmission mechanisms and kinematics. In this paper, an origami parallel module that generates two rotations and one translation is integrated with a twisting module and a compliant gripper to form a novel four-degree-of-freedom grasper. The rotational motion leads to the pitch and yaw motion of the gripper, while the translational motion is converted to a roll motion of the gripper via the twisting module that is stacked on top of the parallel module. In light of plane-symmetric properties of the origami structure in the parallel module, both inverse and forward kinematics are resolved with a geometric approach, revealing a unique joint space and a kinematic mapping of the parallel module, leading to the design of two sets of on-board actuation systems. During the analysis, bending motion of a central spring and static properties of the compliant gripper are modeled using finite-element methods. The structure of the twisting module for motion transmission of the grasper is designed and fabricated using origami folding techniques. Gripping forces of the compliant gripper are evaluated in experimental tests. Further analyses of the system performance are addressed in accordance with the scaling ratio of miniaturization and the scalability of the system is demonstrated by a millimeter-sized origami parallel module produced by the smart composite microstructure fabrication process.

Direction‐cosine‐matrix‐based attitude control subject to actuator saturation

Set-point attitude control of a rigid body explicitly preventing actuator saturation is considered. The attitude control approach developed does not employ any sort of direction-cosine-matrix (DCM) parameterisation, such as Euler angles or quaternions. Rather, the DCM is used directly within the feedback control algorithm. Together a proportional control term and an angular velocity control term make up the attitude controller. The angular velocity control is composed of a strictly positive real system subject to a special input non-linearity. The specific form of the proportional control and angular velocity control ensure control torques are below the saturation level of the on-board actuators. Two controller synthesis methods are considered. The first uses the linearised system, the solution to the linear quadratic regulator problem, and the Kalman–Yakubovich–Popov lemma to design the controller. The second employs a simple low-pass filter that is guaranteed to stabilise the closed-loop system; tuning the low-pass filter is also considered. Numerical simulation results demonstrate effective closed-loop control in the presence of plant disturbances and sensor noise.

Laparoscopic Tissue Retractor Based on Local Magnetic Actuation

Magnetic instruments for laparoscopic surgery have the potential to enhance triangulation and reduce invasiveness, as they can be rearranged inside the abdominal cavity and do not need a dedicated port during the procedure. Onboard actuators can be used to achieve a controlled and repeatable motion at the interface with the tissue. However, actuators that can fit through a single laparoscopic incision are very limited in power and do not allow performance of surgical tasks such as lifting an organ. In this study, we present a tissue retractor based on local magnetic actuation (LMA). This approach combines two pairs of magnets, one providing anchoring and the other transferring motion to an internal mechanism connected to a retracting lever. Design requirements were derived from clinical considerations, while finite element simulations and static modeling were used to select the permanent magnets, set the mechanism parameters, and predict the lifting and supporting capabilities of the tissue retractor. A three-tier validation was performed to assess the functionality of the device. First, the retracting performance was investigated via a benchtop experiment, by connecting an increasing load to the lever until failure occurred, and repeating this test for different intermagnetic distances. Then, the feasibility of liver resection was studied with an ex vivo experiment, using porcine hepatic tissue. Finally, the usability and the safety of the device were tested in vivo on an anesthetized porcine model. The developed retractor is 154 mm long, 12.5 mm in diameter, and weights 39.16 g. When abdominal wall thickness is 2 cm, the retractor is able to lift more than ten times its own weight. The model is able to predict the performance with a relative error of 9.06 ± 0.52%. Liver retraction trials demonstrate that the device can be inserted via laparoscopic access, does not require a dedicated port, and can perform organ retraction. The main limitation is the reduced mobility due to the length of the device. In designing robotic instrument for laparoscopic surgery, LMA can enable the transfer of a larger amount of mechanical power than what is possible to achieve by embedding actuators on board. This study shows the feasibility of implementing a tissue retractor based on this approach and provides an illustration of the main steps that should be followed in designing a LMA laparoscopic instrument.

Robust Control of a Miniature Ducted-Fan Aerial Robot for Blind Navigation in Unknown Populated Environments

This paper proposes a control strategy for a miniature ducted-fan aerial robot to safely perform flight missions in an unknown densely populated environment. The main novelty of the proposed framework is that the vehicle is assumed to be totally blind, namely the obstacles cannot be sensed a priori. Therefore, the presence of possible accidental contacts with the surrounding environment has to be taken into account. To maintain stability in such a complex scenario, mechanics, and control are co-designed. The proposed control strategy relies on some mechanical properties of the airframe, namely on the relative position of the contact points and of the onboard actuators, and on the design of a supervisor able to detect the presence of a contact only by observing the behavior of the flight control loop. The effectiveness of the obtained results is then demonstrated using experiments conducted on a ducted-fan prototype.

Nonlinear H∞ based underactuated attitude control for small satellites with two reaction wheels

Underactuated attitude control is supposed to be used on spacecraft when failure happens with onboard actuators. One main problem with existing underactuated attitude control designs is their limited capabilities against disturbances. In order to solve this problem, an approach based on the theory of H∞ is proposed in this paper. Two propositions are derived from the H∞ theory to improve the robustness of one popular underactuated attitude control design, which was presented by Tsiotras et al. It is proved mathematically that the controller satisfying these two propositions respectively can stabilize the underactuated attitude system locally or globally. The numerical simulations show that the improved controllers based on the H∞ theory could provide higher pointing accuracy for small satellites against disturbances. This validates the effectiveness of the proposed H∞ based approach to improve existing underactuated attitude control designs.

Autonomous undulatory serpentine locomotion utilizing body dynamics of a fluidic soft robot

Soft robotics offers the unique promise of creating inherently safe and adaptive systems. These systems bring man-made machines closer to the natural capabilities of biological systems. An important requirement to enable self-contained soft mobile robots is an on-board power source. In this paper, we present an approach to create a bio-inspired soft robotic snake that can undulate in a similar way to its biological counterpart using pressure for actuation power, without human intervention. With this approach, we develop an autonomous soft snake robot with on-board actuation, power, computation and control capabilities. The robot consists of four bidirectional fluidic elastomer actuators in series to create a traveling curvature wave from head to tail along its body. Passive wheels between segments generate the necessary frictional anisotropy for forward locomotion. It takes 14 h to build the soft robotic snake, which can attain an average locomotion speed of 19 mm s−1.

Actuator Constrained Optimal Formation Keeping Near the Libration Points

Spacecraft formations that evolve near the libration points of the Sun—Earth/Moon system are one option commonly considered for space-based interferometry applications. Although precision tracking is often envisioned as a requirement, earlier studies have already revealed that the dynamically sensitive nature of this region of space presents a number of unique challenges in this respect. For instance, physical hardware limitations, specifically related to the on-board actuators, can limit the attainable tracking accuracy. The goal of this investigation is to devise a numerical process that allows the designer to identify the maximum tracking accuracy achievable in the presence of actuator (e.g., thruster) constraints. This is accomplished through the application of direct optimization methods. A problem formulation is presented that effectively treats, within a nonlinear programming framework, problems with state and control discontinuities and problems involving temporally continuous but spatially discrete control variables. The results of this investigation lay the algorithmic foundation for future explorations involving multiple independent actuators each with its own set of constraints and switching dependencies.

Modelling of Actuator Dynamics for Spacecraft Attitude Control

S PACECRAFT mission success is often highly dependent on the performance and robustness of the attitude control system, which consists of different types of actuators, such as reaction control thrusters, reaction wheels, and magnetic actuators. Solutions to spacecraft attitude control problems often rely on inherent assumptions that the onboard actuators are able to deliver the exact torque desired by the attitude controller at a specified time. The actuators are thus assumed to have no dynamics, or the actuator dynamics are assumed to be fast enough to allow them to be neglected. Although this has shown to be a sufficient approach in the past, it is obvious that attitude actuators, as all electromechanical devices, have dynamics that might impact controller performance. With an increasing demand for high-precision attitude control for purposes such as formation control and optical intersatellite links, the necessity of including actuator dynamics within the control solution is increasingly evident. Mathematical modelling of the complex and nonideal dynamical behavior of actuators and its influence on spacecraft attitude control is a cumbersome task. This dynamical behavior has traditionally been found through laboratory testing, and the subsequent controller design has been influenced by these considerations. One example in this direction is the requirement of reaction thruster response delays being less than the duration of the minimum activation pulse of the actuator. There exist, however, theoretical results from themodelling and analysis of actuator dynamics, such as in [1], in which the effect of unmodelled fast actuator dynamics on the output feedback stabilization of feedback linearizable systems is studied. Similarly, in [2,3], the robust stabilization of a class of nonlinear systems in the presence of unmodelled actuator and sensor dynamics is investigated. More applicable results for our purpose are found in [4,5], in which general multiple-input/multiple-output (MIMO) linear actuator models for underwater vehicle thrusters with dynamics are presented. Because underwater vehicle thrusters are essentially propellers connected to dc motors, analogous to, for example, reaction wheels for spacecraft attitude control, is it possible to describe other actuators with the same model subject to minor changes and tuning. In this paper, we substantiate a unified mathematical model of various attitude control actuators for space applications, in particular, reaction thrusters, reaction wheels, and magnetic torquers. The general actuator dynamical model is based on the marine technology work of [5], appropriately fitted to the aforementioned actuator categories. To describe time delays in the response of actuators such as, for example, thrusters, an expansion of the general actuatormodel is suggested.