Set Of Actuators Research Articles

Synergetic approach in attitude control of very flexible satellites by means of thrusters and PZT devices

The interaction between angular motion and flexible vibrations can heavily affect the stability of the spacecraft. Many control strategies have been developed for solving this issue. Some of them are focused on the attitude dynamics while a different approach consists in facing the problem from the structural point of view, trying to actively damp the vibrations induced by the attitude control, using smart material (like piezoelectric) devices.In this research, an approach unifying the two aspects is proposed. The satellite is modeled as a flexible multibody system, in which the two sets of actuators (attitude and structural devices) are commanded by means of a common sliding mode control algorithm. In such a way, the two systems are not considered as competitors (each one trying to cancel the disturbing effects caused by the other one), but they are cooperating for the common goal of acquiring a desired attitude in a given time without residual oscillations. This synergetic approach is first developed in a numerical environment, then it is tested by means of a free-floating platform equipped with flexible appendages, designed and built as a multilayer composite material with a net of embedded PZT patches (sensors and actuators). The overall navigation and control loop is based on the information coming from the Inertial Measurement Unit and from the PZT sensors, which are filtered and sent to the Synergetic controller, with the goal of reaching a desired attitude. The output of the Synergetic controller consists in both the thrusters firing sequence and the PZT actuators voltage difference required to reach the goal. The experimental results are compared with the ones obtained by more classic approaches (attitude and structural control computed independently), commenting both advantages and drawbacks of the different approaches.

Consistent Manufacturing Device for Coiled Polymer Actuators

Coiled polymer actuators are fabricated by heating a twisted nylon fishing filament. This paper provides a detailed review of their manufacturing process and proposes a method which manufactures these actuators consistently to improve the predictability of their behavior. Two devices are presented: a device that prepares consistent filament sections, and another that twists and coils the filament. Seven successful actuators are produced using the proposed method and compared with seven actuators produced using a method featured in other studies. The behavior of both sets of actuators is then compared using tensile tests on an Instron universal testing machine. The actuators manufactured using the device demonstrate a lower fail rate and produce more force on average. However, the average force produced by each actuator using the proposed method varied slightly. It is believed this fluctuation is due to inconsistent resistance wire lengths and the actuator end loop creation technique. Both of which would require additional improvement.

Cascaded Reference Governor–MPC for Motion Control of Two-Stage Manufacturing Machines

Two-stage processing machines for manufacturing are equipped with two sets of actuators for motion control with different operating ranges and bandwidths. The processing time, product quality, and flexibility of the manufacturing process can be optimized by coordinating these actuators and exploiting the entire actuator operating range. We propose a motion control strategy for two-stage processing machines based on the model predictive control (MPC). By exploiting timescale separation, we formulate the problem as a single-stage motion control with reference-dependent constraints. The feasibility of the MPC problem is guaranteed by using a reference governor that adjusts the feed rate. The proposed method guarantees correct processing while satisfying the actuators’ range and dynamics constraints, finite-time processing of a given spatial pattern, and real-time execution even with limited computational resources. Simulation and experimental results on a real processing pattern are shown for a scaled laboratory demonstration machine.

Design, development, and flight testing of the vertical take-off and landing GNC testbed EAGLE

Precise landing on planets, moons, and other larger celestial bodies requires powered descent, hovering, and vertical landing. Similarly, recent and future concepts for re-usable launch vehicle (RLVs) also involve a vertical take-off and landing. The development of guidance, navigation, and control (GNC) for this type of vehicles is a challenging task. To support this, a vertical take-off and landing vehicle has been developed for demonstrating the capability of conducting soft landings, smooth ascent, and hovering. The focus was put on a platform for testing new and advanced guidance, navigation, and control (GNC) algorithms that employ a base set of sensors and actuators typically present on such vehicles. It should represent a dynamics similar to a thrust vector controlled planetary lander or RLV, and should allow fast turn-around times as well as rapid prototyping capabilities for testing. In addition, the platform should provide the option for an additional small payload, e.g., enhancing the on-board avionics with different or more precise sensors. The result of this platform development is EAGLE (environment for autonomous GNC landing experiments). Its lift-off mass is about \(30\, \text{kg}\) and it is powered by a jet engine with a maximum thrust of \(400\, \text{N}\).

Tokamak-agnostic actuator management for multi-task integrated control with application to TCV and ITER

The plasma control system (PCS) of a long-pulse tokamak must be able to handle multiple control tasks simultaneously, and must be capable of robust event handling with a limited set of actuators. For ITER, this is particularly challenging given the large number of actuator-conflicting control requirements. To deal with these issues, this work develops a task-based approach, where a plasma supervisory controller and an actuator manager make high-level decisions on how to handle the considered control tasks, using generic actuator resources and controllers. This simplifies the interface for operators and physicists since the generic control tasks (instead of controllers) can be directly defined from the general physics goals. This approach also allows one to decompose the PCS into a tokamak-dependent layer and a tokamak-agnostic layer. The developed scheme is first implemented and tested on TCV for simultaneous β control, neoclassical tearing mode (NTM) control, central co-current drive, and H-mode control tasks. It is then applied to an ITER test scenario to prove its flexibility and applicability to systematically handle a large number of tasks and actuators.

Evaluation of log‐of‐power extremum seeking control for wind turbines using large eddy simulations

AbstractThe extremum seeking control (ESC) algorithm has been proposed to determine operating parameters that maximize power production below rated wind speeds (region II). This is usually done by measuring the turbine's power signal to determine optimal values for parameters of the control law or actuator settings. This paper shows that the standard ESC with power feedback is quite sensitive to variations in mean wind speed, with long convergence time at low wind speeds and aggressive transient response, possibly unstable, at high wind speeds. The paper also evaluates the performance, as measured by the dynamic and steady state response, of the ESC with feedback of the logarithm of the power signal (LP‐ESC). Large eddy simulations (LES) demonstrate that the LP‐ESC, calibrated at a given wind speed, exhibits consistent robust performance at all wind speeds in a typical region II. The LP‐ESC is able to achieve the optimal set‐point within a prescribed settling time, despite variations in the mean wind speed, turbulence, and shear. The LES have been conducted using realistic wind input profiles with shear and turbulence. The ESC and LP‐ESC are implemented in the LES without assuming the availability of analytical gradients.

Semi-automatically optimized calibration of internal combustion engines

Modern combustion engines incorporate a number of actuators and sensors that can be used to control and optimize the performance and emissions. We describe a semi-automatic method to simultaneously measure and calibrate the actuator settings and the resulting behavior of the engine. The method includes an adaptive process for refining the measurements, a data cleaning step, and an optimization procedure. The optimization works in a discretized space and incorporates the conditions to describe the dependence between the actuators and the engine behavior as well as emission bounds. We demonstrate our method on practical examples.

Control allocation-based fault tolerant control

This paper describes a novel scheme for fault tolerant control using a robust optimal control design method. This scheme can also be employed as actuator redundancy management for over-actuated linear systems. In contrast to many existing methods in the literature, this scheme can be applied to systems whose control input matrix cannot be factorised into two matrices whose ranks are equal and less than the minimum of the number of columns and rows of the input matrix. The so-called virtual control, in this scheme, is calculated using a robust ℋ2-based feedback design approach constructed to be robust against uncertainties emanating from visibility of the control allocator to the controller and imperfection in the estimated effectiveness gain. Then, using a new control allocation scheme along with a novel Tikhonov-based re-distributor mechanism, the obtained virtual control signal is re-distributed among remaining (redundant or non-faulty) set of actuators. As the proposed scheme is modular-based, it can be employed as a real-time fault tolerant control scheme with no need to reconfigure the controller in the case of actuator faults or failures. The effectiveness of the proposed scheme is demonstrated by a numerical example.

Development of procedures for determining the parameters of an aircraft servo actuator

Main trends in the use of electro-hydraulic actuators and requirements to parameters were discussed. Necessity of using automatic methods for testing an electro-hydraulic actuator together with the standard hardware of the electronic control unit was substantiated. The procedures for testing the control loop of an electro-hydraulic actuator set forth in this study make it possible to eliminate effects of mutual influence of dynamic and static characteristics of the actuator and hardware of the electronic control unit. Procedures for automatic identification of the actuator model and procedures for automatic determination of main parameters and characteristics of the actuator such as zero shift, dead space, amplitude-frequency, phase-frequency and speed characteristics have been proposed. When introducing the proposed procedures, the problem of processing high-speed characteristics of the actuator having high noisiness associated with the pulse nature of the derivative of the discrete signal of the actuator position (12 bits) was solved. In order to avoid introduction of errors in the waveform, in addition to standard digital filtering methods, it was proposed to approximate the noisy actuator characteristic by means of the Bezier curve. A procedure was proposed to record hysteresis of the speed characteristic by means of a cycle of continuous change of speed of movement of the output link of the actuator during the working stroke. The method for automatic identification of a simplified actuator model can significantly reduce labor costs in processing of experimental data. The parameters of the actuator model obtained for various deviations in parameters and various actuator operating conditions (external factors) can improve quality of synthesis of control algorithms

Intelligent multi-agent system for water reduction in automotive irrigation processes

This paper deals with a multi-agent system (MAS) to automate the gathering and managing of information from potato crops in order to provide a precision irrigation system. The proposal and development of a novel MAS is presented based on different agent subsystems with specific objectives to meet the main objective of the global MAS. The proposed MAS has been developed on the Cloud Computing paradigm and is able to gather data from wireless sensor networks (WSNs) located in potato crops for knowledge discovery and decision making. According to the collected information as historical data by the MAS, it can make decision on an actuator set that modify the irrigation system by updating the areas of the crop with most irrigation needs. The use of these intelligent technologies in rural areas provides a considerable saving of resources and improves the efficiency and effectiveness of agricultural production systems. The architecture has been tested in an agricultural environment in order to optimize irrigation in a potato crop. The results showed a significant reduction in comparison to traditional automotive irrigation.

Linear Piezoelectric Motor for Topography Detector of Diamond Wire

In topography detection procedures for diamond wire, precision motion control is one of the key preconditions; the motion control unit of detection needs both micron resolutions and centimeter strokes. In this paper, a linear motor with four sets of multilayer piezoelectric actuators was developed to achieve an actuator with high resolution and a large stroke. The stroke depended on the guideways of the system, which mar enlarged the stroke of a single multilayer piezoelectric actuator. The mechanism of differential actuation was analyzed by dividing an operation cycle into several states. A symmetrically arranged four-foot design was proposed, and a corresponding excitation method was devised. A prototype was fabricated to conduct a proof-of-concept operation test. Experimental results validated the feasibility of the prototype with a 10 mm stroke. The speed of the prototype increased when the amplitudes of driving voltage signals increased from 30 V to 100 V. Within the frequency range of 1 Hz to 120 Hz, the speed increased initially then decreased with driving frequency, the maximum of which was at 100 Hz. With an excitation voltage signal of 100 V and 100 Hz, the speed reached a maximum of 740 μm/s. With an excitation voltage signal of 30 V and 120 Hz, the resolution of the prototype reached 0.26 μm. The prototype satisfies precision motion control of topography detection for diamond wire. This work also provides an option for automatic systems that require high resolutions and large strokes.

A Non-linear approach to dynamic torque modelling for expedited engine characterisation, control and calibration

Abstract Traditional approaches to engine torque mapping apply steady or quasi-steady-state approaches for data collection. Engine actuators are moved to some set-point and the engine is left to stabilise. Data is then recorded at fixed actuator settings over a period of time and averaged, the size of the averaging ‘window’ is often arbitrarily chosen. Such methods are time intensive and inefficient with the majority of the time available for data collection wasted. In this paper, a novel and fully transient characterisation methodology is introduced. Dynamic excitation signals are used in this work to significantly increase the rate of data collection and settling time (after an initial warm-up) is no longer required. Engine dynamic behaviour is described using first-order conditionally linear repeated measurement models, these reflect the inherent structure of the torque data that is a consequence of the experimental method employed. Model parameters are determined using Maximum Likelihood Estimation (MLE). To abstract steady-state data from the dynamic models (a requirement of legacy controllers) the models are extrapolated, in time, for fixed input settings. The efficacy of the extrapolation procedure is clearly demonstrated through direct comparison with actual steady-state sweeps utilised for validation of the method. The approach is shown to be seven times faster than conventional methods based on slow ramps or steady-state test.

Design and Testing of a Co-Rotating Vibration Excitation System

A vibration excitation system (VES) in a form of an active coupling is proposed, designed and manufactured. The system is equipped with a set of piezoelectric stack actuators uniformly distributed around the rotor axis and positioned parallel to each other. The actuator arrangement allows an axial displacement of the coupling halves as well as their rotation about any transverse axis. Through the application of the VES an aimed vibration excitation is realised in a co-rotating coordinate system, which enables a non-invasive and precise modal analysis of rotating components. As an example, the VES is applied for the characterisation of the structural dynamic behaviour of a generic steel rotor at different rotational speeds. The first results are promising for both stationary and rotating conditions.

Motion planning strategies in human control of non-rigid objects with internal degrees of freedom

The paper deals with modeling of human-like reaching movements in dynamic environments. A simple but not trivial example of reaching in a dynamic environment is the rest-to-rest manipulation of a multi-mass flexible object with the elimination of residual vibrations. Two approaches to the prediction of reaching movements are formulated in position and force actuation settings. In the first approach, either the position of the hand or the hand force is specified by the lowest order polynomial satisfying the boundary conditions of the reaching task. The second approach is based on the minimization of either the hand jerk or the hand force-change, with taking into account the dynamics of the flexible object. To verify the resulting four mathematical models, an experiment on the manipulation of a ten-masses flexible object of low stiffness is conducted. The experimental results show that the second approach gives a significantly better prediction of human movements, with the minimum hand force-change model having a slight but consistent edge over the minimum hand jerk one.

Design and Evaluation on a New Dynamical Lubricity Tester

Development of modern drilling has placed greater demands on lubricity inspection. The traditional lubricity testers appear to be very limited due to a lack of real-time measurement in the high temperature high pressure (HTHP) conditions. In the present work, a novel HTHP dynamic lubricity tester has been specially designed. This tester comprises five main parts: a driving part, a set of HPHT actuators, a loading unit, a test chamber, and a computational control part. Special friction interfaces encountered in downhole can be effectively simulated. Testing temperature and pressure can be controlled up to 150°C and 10MPa, respectively. The applicability of the tester has been evaluated by measuring lubricity of the typical PRD fluid in the pressure range of 1.5MPa∼3.5MPa. This newly designed lubricity tester can provide instructive information on optimization of modern drilling process.

Adaptive Backstepping Tracking Control for an over–Actuated DP Marine Vessel with Inertia Uncertainties

Abstract Designing a tracking control system for an over-actuated dynamic positioning marine vessel in the case of insufficient information on environmental disturbances, hydrodynamic damping, Coriolis forces and vessel inertia characteristics is considered. The designed adaptive MIMO backstepping control law with control allocation is based on Lyapunov control theory for cascaded systems to guarantee stabilization of the marine vessel position and heading. Forces and torque computed from the adaptive control law are allocated to individual thrusters by employing the quadratic programming method in combination with the cascaded generalized inverse algorithm, the weighted least squares algorithm and the minimal least squares algorithm. The effectiveness of the proposed control scheme is demonstrated by simulations involving a redundant set of actuators. The evaluation criteria include energy consumption, robustness, as well accuracy of tracking during typical vessel operation.

Cost-aware securing of IoT systems using attack graphs

The Internet of Things (IoT) contains a diverse set of sensors, actuators and other Internet-connected devices communicating, processing data and performing a multitude of functions. It is emerging as an integral part of societal infrastructure enabling smart services. However, these connected objects might have various vulnerabilities that can lead to serious security compromises and breaches. Securing and hardening of IoT systems is thus of vital importance. In that regard, attack graphs provide analytical support to prevent multistep network attacks by showing all possible sequences of vulnerabilities and their interactions. Since attack graphs generally consist of a very large number of nodes, it is computationally challenging to analyze them for network hardening. In this paper, we propose a greedy algorithm using compact attack graphs to find a cost-effective solution to protect IoT systems. First, we extract all possible attack paths which reach predetermined critical resources embedded in the network. Then, exploit or initial condition with minimum effective cost is selected to be removed. This cost is calculated as a function of contribution to attack paths (the higher, the better) and removal cost (the lower, the better). This process continues iteratively until the total cost exceeds the allocated budget. The experimental results show that our algorithm scales almost linearly with the network size and it can be applied to large-scale graphs with a very large number of IoT nodes. In addition to network-hardening, our proposal measures the security level of the network in every step to demonstrate the vulnerability grade of the system.

Static output feedback fault tolerant control using control allocation scheme

SummaryThis paper describes two novel schemes for fault tolerant control using robust suboptimal static output feedback design methods. These schemes can also be employed as actuator redundancy management for overactuated uncertain linear systems. In contrast to many existing methods in the literature that assume the control input matrix (i) is not of full‐rank such that it can be factorized into two matrices and (ii) it does not involve uncertainty, these schemes can be applied to systems whose control input matrix cannot be factorized and/or involve uncertainty. The so‐called virtual control, in these schemes, is calculated using suboptimal ‐based static output feedback design schemes constructed to be robust against uncertainties emanating from inherent input matrix uncertainty and visibility of the control allocator to the controller. Then, using two proposed control allocation schemes (fixed and on‐line), the obtained virtual control signal is redistributed among remaining (redundant or nonfaulty) set of actuators. As the proposed schemes are modular‐based, they can be employed as real‐time fault tolerant control schemes with no need to reconfigure the controller in the case of actuator faults or failures. The effectiveness of the proposed schemes is discussed and compared with numerical examples.

On steady-state disturbance compensability for actuator placement in adaptive structures

Abstract Adaptive structures in civil engineering are mechanical structures with the ability to modify their response to external loads. Actuators strongly affect a structure’s adaptivity and have to be placed thoughtfully in the design process to effectively compensate external loads. For constant loads, this property is introduced as steady-state disturbance compensability. This property can be linked to concepts from structural engineering such as redundancy or statical indeterminacy, thus representing an interdisciplinary approach. Based on the disturbance compensability matrix, a scalar performance metric is derived as quantitative measure of a structure’s ability to compensate the output error for arbitrary constant disturbances with a given set of actuators. By minimizing this metric, an actuator configuration is determined. The concept is applied to an example of a truss structure.

Sensors usage in electro-pneumatic systems

The article presents a description of the FESTO DI-DACTIC laboratory stand, consisting of a assembly table, a set of actuators, electro-pneumatic valves, proximity compo-nents and FluidSim-P software. In pneumatic and electro-pneumatic control systems, ef-fective operation depends on the possibility of using sensors and their correct operation. Sensors that work without con-tact have been widely used.