Onboard Actuators Research Articles

Implementation of real-time hybrid simulation using a large shake table with onboard actuators

In recent decades, shake table real-time hybrid simulation (RTHS) has emerged as a promising seismic testing approach for complex engineering structures. However, the current shake table RTHS systems with actuators typically install the dynamic actuators on a reaction wall outside the table, which introduce interaction issues between the dynamic actuators and the shake table. This study proposes a potential improvement by developing a shake table RTHS platform with onboard actuators. The platform incorporates a 6 m × 9 m large-scale shake table where the physical substructure, two dynamic actuators, and the reaction frame are all positioned. To validate the effectiveness of the developed platform, a two-story steel frame is tested by both full structure shake table test and substructure shake table RTHS. In the shake table RTHS, the lower part of the frame serves as the physical substructure and is simultaneously loaded by the shake table and dynamic actuators, while the upper part is numerically analyzed in OpenSees, using OpenFresco and Simulink as intermediate softwares. The test results demonstrate that the developed shake table RTHS platform provides reasonable predictions to the structural seismic responses. In addition, time delay is optimized using both inner and outer loop compensators, highlighting the effectiveness of inverse compensation and adaptive time series (ATS) compensation schemes. This paper successfully develops a shake table RTHS platform using a large shake table with onboard dynamic actuators, providing a valuable seismic testing platform for RTHS of large-scale complex engineering structures.

Self‐Sustained and Coordinated Rhythmic Deformations with SMA for Controller‐Free Locomotion

This study presents a modular, electronics‐free, and fully onboard control and actuation approach for shape memory alloy (SMA)‐based soft robots to achieve locomotion tasks. This approach exploits the nonlinear mechanics of compliant curved beams and carefully designed mechanical control circuits to create and synchronize rhythmic deformation cycles, mimicking the central pattern generators prevalent in animal locomotions. More specifically, the study elucidates a new strategy to amplify the actuation performance of the shape memory coil actuator by coupling it to a carefully designed, monostable curve beam with a snap‐through buckling behavior. Such SMA‐curved beam assembly is integrated with an entirely mechanical circuit featuring a slider mechanism. This circuit can automatically cut off and supply current to the SMA according to its deformation status, generating a self‐sustained rhythmic deformation cycle using a simple DC power supply. Finally, this study presents a new strategy to coordinate (synchronize) two rhythmic deformation cycles from two robotic modules to achieve efficient crawling locomotion but still use a single DC power. This work represents a significant step toward fully autonomous, electronics‐free SMA‐based locomotion robots with fully onboard actuation and control.

Probabilistic evaluation of dynamic positioning operability with a Quasi-Monte Carlo approach

During the design phase of an offshore unit, estimating the station-keeping capabilities of the dynamic positioning (DP) system is mandatory. This means, in conventional offshore applications, to determine the maximum sustainable wind speed as a function of the encounter heading, which the unit may counteract by employing the onboard actuators or mooring lines only. Besides the deterministic estimation of DP capability, it is possible to assess the operability of the DP system following a non-deterministic probabilistic process by employing the site-specific joint wind-wave distributions to model the environment. In such a case, the operability results from a Monte Carlo integration process. Here it is proposed to enhance the applicability of the probabilistic analysis of DP operability, investigating the application of a Quasi-Monte Carlo method. In this sense, the procedure uses quasi-random samplings following a Sobol sequence instead of employing random samples of the joint distributions. In this paper, the Quasi-Monte Carlo process is tested and compared on a reference ship, highlighting the improvements to the established probabilistic DP prediction concerning the number of calculations needed to estimate operability. The significant reduction of computational time makes the newly implemented method suitable for the early design stage applications.

Attitude Stabilization of a Satellite with Large Flexible Elements Using On-Board Actuators Only

Attitude control of a satellite with three flexible elements is considered. Control torque is developed by a set of reaction wheels, which are installed on the central hub of the satellite. The flexible elements are large, so the control torque constraints must be taken into account. In the paper, a control algorithm based on a linear-quadratic regulator is studied. The asymptotic stability of this control is shown. The choice of the control parameters is based on the closed form solution of the corresponding algebraic Riccati equation, which is supplemented by the linear matrix inequality. To increase the convergence rate, particle swarm optimization is used to tune the control parameters.

Designing an adaptive robust observer for underactuation fault diagnosis of a remote sensing satellite

SummaryThis paper mainly aims at the underactuated case diagnosis due to an actuator failure for a remote sensing satellite. We consider healthy initial conditions for the actuators to investigate the underactuation fault in an attitude tracking control problem. Reaction wheels are the onboard actuators, and a new fault injection mechanism on the speed characteristic is introduced using the multi‐fault function. The fault detection and diagnosis strategy is based on the sliding mode and adaptive sliding mode observers in a finite‐time decision window. The robust observer and adaptive threshold are designed to detect the fault, and the adaptive robust observer estimates the fault model. The residual signal is evaluated by forming the window with fixed thresholds, and in the decision steps, priority is given to the underactuation fault diagnosis. System performance is presented for two actuator fault scenarios in a snapshot imaging mode to understand this case clearly. Numerical simulations close to in‐orbit conditions confirm the satisfactory performance of the proposed strategy that underactuated case is diagnosed by injecting stuck and idle faults around 2.19 and 3.52 s. The times obtained in this study are guaranteed with a 3‐sigma confidence level statistical characteristic. Furthermore, the results of the present work are validated using an air‐bearing experimental test bed to illustrate a more realistic behavior of an underactuated satellite.

A novel optimal control strategy for regenerative active suspension system to enhance energy harvesting

The conventional onboard actuators in the active suspension system (ASS) consume a high amount of external energy, which restricts their application in reducing the effects of vehicle body vibration caused by road roughness. To address this limitation, the energy-regenerative active suspension system (RASS) based on the electromagnetic structure has been introduced. This paper presents a new optimal control algorithm for the RASS that directly considers energy regeneration in combination with ride comfort in its performance index. The proposed algorithm can be tuned to direct the working points towards high energy regeneration zones. Meanwhile, it employs a realistic nonlinear model of the suspension system to achieve high performance. By applying proper operating electric circuits, the performance of the RASS under the proposed controller is studied for various road conditions. The obtained results indicate that the proposed control strategy delivers lower acceleration over the human body-sensitive frequency range based on ISO2631-1, despite harvesting energy. For instance, when the vehicle travels on a random road with a velocity of 12 m/s, the proposed nonlinear control strategy with a suitable weighting factor increases the capacitor voltage from the initial value of 20 V to 40 V during a 15 s interval. This shows a 31% increase compared to the case where the weighting factor is taken to be zero, according to the previous strategies. Additionally, the proposed strategy by the nonlinear controller remarkably increases the harvested energy compared with a linear optimal controller.

Insect-scale jumping robots enabled by a dynamic buckling cascade

Millions of years of evolution have allowed animals to develop unusual locomotion capabilities. A striking example is the legless-jumping of click beetles and trap-jaw ants, which jump more than 10 times their body length. Their delicate musculoskeletal system amplifies their muscles' power. It is challenging to engineer insect-scale jumpers that use onboard actuators for both elastic energy storage and power amplification. Typical jumpers require a combination of at least two actuator mechanisms for elastic energy storage and jump triggering, leading to complex designs having many parts. Here, we report the new concept of dynamic buckling cascading, in which a single unidirectional actuation stroke drives an elastic beam through a sequence of energy-storing buckling modes automatically followed by spontaneous impulsive snapping at a critical triggering threshold. Integrating this cascade in a robot enables jumping with unidirectional muscles and power amplification (JUMPA). These JUMPA systems use a single lightweight mechanism for energy storage and release with a mass of 1.6 g and 2 cm length and jump up to 0.9 m, 40 times their body length. They jump repeatedly by reengaging the latch and using coiled artificial muscles to restore elastic energy. The robots reach their performance limits guided by theoretical analysis of snap-through and momentum exchange during ground collision. These jumpers reach the energy densities typical of the best macroscale jumping robots, while also matching the rapid escape times of jumping insects, thus demonstrating the path toward future applications including proximity sensing, inspection, and search and rescue.

A Torsion-Bending Antagonistic Bistable Actuator Enables Untethered Crawling and Swimming of Miniature Robots.

Miniature robots show great potential in exploring narrow and confined spaces to perform various tasks, but many applications are limited by the dependence of these robots on electrical or pneumatic tethers to power supplies outboard. Developing an onboard actuator that is small in size and powerful enough to carry all the components onboard is a major challenge to eliminate the need for a tether. Bistability can trigger a dramatic energy release during switching between the 2 stable states, thus providing a promising way to overcome the intrinsic limitation of insufficient power of small actuators. In this work, the antagonistic action between torsional deflection and bending deflection in a lamina emergent torsional joint is utilized to achieve bistability, yielding a buckling-free bistable design. The unique configuration of this bistable design enables integrating of a single bending electroactive artificial muscle in the structure to form a compact, self-switching bistable actuator. A low-voltage ionic polymer-metal composites artificial muscle is employed, yielding a bistable actuator capable of generating an instantaneous angular velocity exceeding 300 °/s by a 3.75-V voltage. Two untethered robotic demonstrations using the bistable actuator are presented, including a crawling robot (gross weight of 2.7 g, including actuator, battery, and on-board circuit) that can generate a maximum instantaneous velocity of 40 mm/s and a swimming robot equipped with a pair of origami-inspired paddles that swims breaststroke. The low-voltage bistable actuator shows potential for achieving autonomous motion of various fully untethered miniature robots.

Nanorobots with Hybrid Biomembranes for Simultaneous Degradation of Toxic Microorganism

Nanorobotics is a modern technological sector that creates robots with elements that are close to or near the nanoscale scale of such a nanometer. To be more specific, nanorobotics has been the nanotechnology approach to designing and creating nanorobots. Also, with the fast growth of robotics technology, developing biomaterials micro- or nanorobots, which convert biological concepts into a robotic device, grows progressively vital. This proposes the development, manufacturing, and testing of a dual–cell membrane–functionalized nanorobot for multifunctional biological threat component elimination, with a focus on the simultaneous targeted and neutralization of the pathogenic bacteria and toxins. Ultrasound-propelled biomaterials nanorobots comprised of the gold nanostructures wrapped in a combination of platelet (PL) and Red Blood Cell (RBC) layers were developed. Biohybrid micro- and nanorobots were small machines that combine biological and artificial elements. They may benefit from onboard actuators, detection, management, and deployment of a variety in medical functions. These hybrid cell walls consist of a variety of structural proteins involved in living organism RBCs and PLs, which provide nanorobots with either a quantity of the appealing biological functionality, with bonding and adhesion to the PL-adhering pathogenic organisms (for example, staphylococcus bacteria) but also neutralization of the pore-forming toxins (e.g., toxin). Furthermore, the biomaterials nanorobots demonstrated quick and efficient extended sonic propulsion for total blood with really no visible bacterial growth and mirrored the movements of genuine cell separation. This propulsion improved the robots’ bonding and detoxifying efficacy against infections and poisons. Overall, combining this diversified physiological activity of hybrid cellular tissue with the energy propulsion of such robotic systems contributed to the dynamic robotics scheme for effective separation and synchronous elimination of various living risks, a significant step towards to development of a broad-spectrum detoxifying robotic framework.

A Survey on Swarm Microrobotics

The small size and wireless actuation of microrobots make them potential candidates for minimally invasive medicine. To advance microrobots to future clinical application, microrobotics researchers have investigated a number of key issues, in which swarm control is a primary challenge and is attracting increasing attention. As a single microrobot has limited volume and surface area, clinically relevant tasks, including <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vivo</i> tracking, usually require simultaneous control of a large swarm of microrobots. Unlike macroscale robots, implementing on-board actuators and sensors for microrobots is challenging, which differentiates swarm microrobotics from other swarm robotics approaches. This article systematically summarizes the state of the art for this emerging field, including actuation systems with different power sources, swarm behaviors modeling and simulation, swarm control strategies, and targeted biomedical applications. Actuation principles of microrobot swarms are categorized in detail, and critical comparisons are made to provide guidance and insight for future swarm microrobotics researchers. Considering the unique features of swarm microrobotics compared to traditional swarm robotics, this article also emphasizes the modeling, simulation, and control of microrobot swarms. Furthermore, recent biomedical applications of microrobot swarms are summarized to illustrate specific application scenarios. Finally, we provide an assessment of the future directions of swarm microrobotics.

Indirect Optimal Control of Advection-Diffusion Fields through Distributed Robotic Swarms

We consider the problem of optimally guiding a large-scale swarm of underwater vehicles that is tasked with the indirect control of an advection-diffusion environmental field. The microscopic vehicle dynamics are governed by a stochastic differential equation (SDE) with drift. The drift terms model the self-propelled velocity of the vehicle and the velocity field of the currents. In the mean-field setting, the macroscopic vehicle dynamics are governed by a Kolmogorov forward equation in the form of a linear parabolic advection-diffusion partial differential equation (PDE). The environmental field is governed by an advection-diffusion PDE in which the advection term is defined by the fluid velocity field. The vehicles are equipped with on-board actuators that enable the swarm to act as a distributed source in the environmental field, modulated by a scalar control parameter that determines the local source intensity. In this setting, we formulate an optimal control problem to compute the vehicle velocity and actuator intensity fields that drive the environmental field to a desired distribution within a specified amount of time. After proving an existence result for the solution of the optimal control problem, we discretize and solve the problem using the Finite Element Method (FEM). We show through numerical simulations the effectiveness of our control strategy in regulating the environmental field to zero or to a desired distribution in the presence of a double-gyre flow field.

Biohybrid Micro- and Nanorobots for Intelligent Drug Delivery.

Biohybrid micro- and nanorobots are integrated tiny machines from biological components and artificial components. They can possess the advantages of onboard actuation, sensing, control, and implementation of multiple medical tasks such as targeted drug delivery, single-cell manipulation, and cell microsurgery. This review paper is to give an overview of biohybrid micro- and nanorobots for smart drug delivery applications. First, a wide range of biohybrid micro- and nanorobots comprising different biological components are reviewed in detail. Subsequently, the applications of biohybrid micro- and nanorobots for active drug delivery are introduced to demonstrate how such biohybrid micro- and nanorobots are being exploited in the field of medicine and healthcare. Lastly, key challenges to be overcome are discussed to pave the way for the clinical translation and application of the biohybrid micro- and nanorobots.

Onboard actuator model-based Incremental Nonlinear Dynamic Inversion for quadrotor attitude control: Method and application

This paper addresses the robust attitude control problem for quadrotors subject to model mismatch and disturbances. A dynamic inversion based attitude control scheme is proposed, which consists of an outer loop attitude controller and an inner loop angular acceleration controller. The attitude controller is designed based on the Nonlinear Dynamic Inversion (NDI) to precisely linearize the nonlinear dynamics between the angular acceleration and the attitude. An onboard actuator model-based Incremental Nonlinear Dynamic Inversion (INDI) controller is designed in the angular acceleration control loop to improve the robustness against the model mismatch and disturbances. Meanwhile, the onboard actuator model with a modified structure eliminates the oscillation phenomenon when the sampling rate of the controller is higher than that of the actuator. Numerical simulations and flight tests demonstrate the effectiveness and robustness of the proposed controller in comparison with the PID controller.

A microrobotic platform actuated by thermocapillary flows for manipulation at the air-water interface.

Future developments in micromanufacturing will require advances in micromanipulation tools. Several robotic micromanipulation methods have been developed to position micro-objects mostly in air and in liquids. The air-water interface is a third medium where objects can be manipulated, offering a good compromise between the two previously mentioned ones. Objects at the interface are not subjected to stick-slip due to dry friction in air and profit from a reduced drag compared with those in water. Here, we present the ThermoBot, a microrobotic platform dedicated to the manipulation of objects placed at the air-water interface. For actuation, ThermoBot uses a laser-induced thermocapillary flow, which arises from the surface stress caused by the temperature gradient at the fluid interface. The actuated objects can reach velocities up to 10 times their body length per second without any on-board actuator. Moreover, the localized nature of the thermocapillary flow enables the simultaneous and independent control of multiple objects, thus paving the way for microassembly operations at the air-water interface. We demonstrate that our setup can be used to direct capillary-based self-assemblies at this interface. We illustrate the ThermoBot's capabilities through three examples: simultaneous control of up to four spheres, control of complex objects in both position and orientation, and directed self-assembly of multiple pieces.

ExoNet Database: Wearable Camera Images of Human Locomotion Environments.

ExoNet Database: Wearable Camera Images of Human Locomotion Environments.

On the forward and backward motion of milli-bristlebots

This works presents the theoretical analysis and experimental observations of the bidirectional motion of a millimeter-scale bristle robot (milli-bristlebot) with an on-board piezoelectric actuator. First, the theory of the motion, based on the dry-friction model, is developed and the frequency regions of the forward and backward motion, along with the resonant frequencies of the system are predicted. Secondly, milli-bristlebots with two different bristle tilt angles are fabricated, and their bidirectional motions are experimentally investigated. The dependency of the robot speed on the actuation frequency is studied, which reveals two distinct frequency regions for the forward and backward motion that matches well with our theoretical predictions. Furthermore, the dependencies of the resonance frequency and robot speed on the bristle tilt angle are experimentally studied and tied to the theoretical model. This work marks the first demonstration of bidirectional motion at the millimeter scales, achieved for bristlebots with a single on-board actuator.

Independent control of multiple magnetic microrobots: design, dynamic modelling, and control

Swimming microrobots have a variety of applications including drug delivery, sensing, and artificial fertilization. Their small size makes onboard actuation very hard, and therefore an external source such as the magnetic field is a practical way to steer and move the robot. In this paper, we have designed a novel microrobot steered by magnetic paddles. We have also discussed design parameters where, based on the conducted simulation, the robot speed reaches 520 um/s. It is shown that the microrobot speed depends on the robot paddle dimensions. According to the microrobots motion characteristics and their different reactions to the same input, we have designed a steering strategy for point-to-point control of multiple microrobots.

Power Optimization in Mobile Robots Using a Real-Time Heuristic

Mobile robots typically run using finite energy resources, supplied by finite batteries. The limitation of energy resources requires human intervention for recharging the batteries. To reduce human intervention, this work focuses on coordinating power in a group of robots. A power optimization subroutine provides some sense of distribution of power by the control unit (CU). A variety of on-board sensors, actuators, and communication modules are controlled by a heuristic-based controller class allowing such components to conserve the current taken from the attached power source. Using the proposed approach, autonomous robots will be aware of their power system, especially regarding battery life. The new approach takes advantage of a heuristic function which uses evaluation values calculated at different times for the different robots. An experimental setup is applied on the team of robots. The optimization module is evaluated on each robot. The results show that the team of mobile robots consumes less energy and more efficient power regulation during their duties. Finally, the application of the proposed optimization technique in a distributed manner achieves good power saving figures when performing the particular task.

Control of bearingless electric machines dedicated for aviation

Purpose The paper presents the results of work on control systems of bearingless electric motors. Authors proposed the applications of bearingless electric machines for aircraft actuation system. Suggested solution characterizes novel concept of on-board equipment design such as More Electric Aircraft. Magnetic suspension technology allows elimination of friction force and the negative performance features of classic bearing system. However, to achieve all these purposes appropriately, dedicated control system must be also applied. Design/methodology/approach The development of a control system of bearingless electric machine is presented in detail. Mathematical model and construction of induction bearingless motor are widely discussed. Then, proportional–integral-derivative controller algorithm designing for BEM control system was presented using the well pole placement method. Simulation model of BEM control system with use of Matlab-Simulink software was shown. Finally, experimental studies on laboratory stand were introduced. The paper presents design methodology of conventional and advanced control system of bearingless motor. Findings The presented concept of the bearingless electric machines could be applied in the on-board actuation system. During research, full control system of bearingless electric motor was designed and tested. This system consisted of two subsystems. The first responded for rotary speed stabilization and second one was designed for position control of the rotor in the air gap. Practical implications The presented concept of the bearingless electric machines could be applied in the on-board actuation system. During research, full control system of bearingless electric motor was designed and tested. This system consisted of two subsystems. The first responded for rotary speed stabilization and second one was designed for position control of the rotor in the air gap. Originality/value The idea of active magnetic suspension system will be implemented for aviation on technology readiness level V. The paper presents unique laboratory stand with bearingless electric motor and experimental studies. The stable time responses of designed control system were presented and discussed. In addition, preliminary considerations of advanced control system with robust controller were introduced as well.

Pilot Assessment of Fault-Tolerant PID Flight Controller for Elevator Efficiency Reduction via Hardware-In-the-Loop Simulations

This note presents the pilot assessment of a Fault-Tolerant Control (FTC) law for elevator efficiency reduction via Hardware-In-the-Loop Simulations (HILS) with a research airplane MuPAL-α. The FTC is supposed to be a PID controller from the viewpoint of the practicality and applicability viz., conventional Stability/Control Augmentation System (S/CAS) structure is adopted. The PID-FTC is designed with the consideration of onboard actuator uncertainties as well as the possible loss of efficiency (from 0% loss up to 80% loss) in the framework of H∞ control with hinfstruct command implemented in Matlab®. In HILS, the pilot is required to have steady climb and descent under the condition that the elevator efficiency is gradually reduced in a software level. HILS results indicate that the designed PID-FTC works well when the elevator efficiency decreases even under wind gust conditions.