Modal Control Strategy Research Articles

Dynamics Modeling and Modal Space Control Strategy of Ship-Borne Stewart Platform for Wave Compensation

Abstract The ship-borne Stewart platform can compensate for the six-degrees-of-freedom (DOFs) motion generated by the ship, which improves the reliability and safety of offshore operations and increases the executable window period. The heavy and off-center load of the gangway significantly influences the high-precision compensation control of the platform. Besides, the gangway assembled on the platform vibrates easily due to its low natural frequency that requires high dynamic performance of the compensating. To deal with the problem mentioned, the modal space control strategy is introduced to fully consider the inertia characteristics. First, based on Kane's method, the complete dynamic model considering the ship's motion and actuator inertia is established. Then, the modal space proportional and derivative (PD) controller (MSPDC) and the modal space sliding mode controller (MSSMC) are designed based on the modal theory. Finally, simulations are carried out to show the advantages of the proposed model and the advantages of proposed controllers in compensation accuracy and anti-interference ability. Furthermore, the significant compensation rate (SCR) is proposed to evaluate the six-DOFs compensation accuracy. Compared with the PD controller with gravity compensation (PDCGC), the position SCR of MSSMC is increased from 95.37% to 99.28%, and the angle SCR increased from 85.57% to 99.65%.

Direct Deadbeat Control of a Buck PWM Converter

The paper explains the shortcomings of the well-known modal control strategy, which prevent its practical application to achieve the highest possible dynamic performance of switching semiconductor converters. A method for eliminating these shortcomings is suggested as applied to a self-contained modal control version with specifying zero roots of the characteristic polynomial and obtaining a nilpotent system matrix. A technique for synthesizing direct deadbeat control with a nilpotent system matrix is described in detail to implement a finite transient that terminates within a number of cycles not exceeding the order of the difference equation with which a discrete system is described. The control object is a well-known circuit of a DC-DC buck converter with an inductive-capacitive filter and a proportional input-output characteristic provided by an integral link in the feedback loop. The efficiency of the proposed deadbeat controller version is confirmed through mathematically simulating the operation of a PWM converter controlling the load current. The dynamic operation modes are studied for the case of a step change in the load resistance and input voltage relative to their nominal values for a control system with I-, PI- and deadbeat controllers. A comparison of the obtained results shows that the transients in the system equipped with a deadbeat controller terminate most quickly: within three cycles without an overshoot. This corresponds to the maximum convergence rate to the equilibrium state for a third-order system.

Semi‐active modal control of structures with lockable joints: general methodology and applications

In this study, a novel modal control strategy by means of semi-actively lockable joints is proposed. The control strategy allows for a directed flow of energy between vibrational modes, which makes it suitable not only for vibration attenuation purposes but also for energy scavenging driven by electromechanical energy harvesters. The proposed control strategy is an extension of the prestress-accumulation release (PAR) technique; however, it introduces also new concepts that increase the efficiency of the overall control system. Contrary to the PAR, the proposed method requires measurement of both strains in the vicinity of the semi-active joints and translational velocities that provide global information about system behavior. The latter aspect requires the control system to be organized within a hierarchical feedback architecture. The benefit from this higher complexity of the control system is its better performance compared to the PAR. The proposed semi-active modal control not only attenuates structural vibration faster, but it also achieves this goal with a smaller number of switches implemented in the joints. The effectiveness of the proposed methodology has been demonstrated on structures equipped with two lockable joints. Two practical examples have been investigated: one employs the concept of vibration-based energy harvesting for a two-story frame structure, while the second one reduces vibration of an eight-story frame structure subjected to kinematic excitation.

Mode shape analysis, modal linearization, and control of an elastic two-link manipulator based on the normal modes

• Global vibration modes of two-link flexible manipulators are calculated. • Effects of uncertainties and design parameter are studied in modal space. • A modal linearization method is proposed for flexible manipulators. • A control scheme based on the linear model is simulated. Accurate determination of mode shapes and resonant frequencies of high-speed slender robotic arms, known as flexible link manipulators, is fundamental for mechanical design, dynamic analysis, identification, and control of the manipulators. This paper presents a Finite Element (FE) modeling, modal analysis, linearization, and control of a Two-Link Flexible Manipulator (TLFM) based on the global vibration modes, which are essentially more precise than the component mode analysis used in most previous studies. The resonant frequencies and the global vibration modes are employed, then, for analyzing the influence of configuration and payload variations, as well as architecture variations using a prismatic joint in the upper arm. The Modal Assurance Criterion (MAC) is adopted as a tool for comparing the mode shapes. Finally, based on the system modes and MAC calculations, a new modal control scheme is proposed for a multi-stage rest-to-rest maneuver of the manipulator.

Optimal design of material microstructure for maximizing damping dissipation velocity of piezoelectric composite beam

The topology optimization method of material microstructure of piezoelectric composite structures is proposed so as to improve the dynamic characteristics of the closed-loop system. The topology optimization model of material microstructure is built, where the design variable is constructed based on the SIMP interpolation scheme and the objective function is to maximize the damping dissipation velocity of the piezoelectric composite structure based on the independent modal control strategy, while the constraints are applied on the volume fractions of the phase materials. The sensitivity formulations of the damping dissipation velocity in modal space with respect to the design variables are derived. A bi-direction evolutionary structural optimization (BESO) method is developed to obtain a clear and optimal topology for material microstructure. The results of several numerical examples show that different initial designs of the base cell, different boundary conditions and the property of the disturbance have effect on the optimal solution. Also, the proposed method can effectively improve the active control performance and reduce structural weight.

Control of a Robotic Hand Using a Tongue Control System-A Prosthesis Application.

The aim of this study was to investigate the feasibility of using an inductive tongue control system (ITCS) for controlling robotic/prosthetic hands and arms. This study presents a novel dual modal control scheme for multigrasp robotic hands combining standard electromyogram (EMG) with the ITCS. The performance of the ITCS control scheme was evaluated in a comparative study. Ten healthy subjects used both the ITCS control scheme and a conventional EMG control scheme to complete grasping exercises with the IH1 Azzurra robotic hand implementing five grasps. Time to activate a desired function or grasp was used as the performance metric. Statistically significant differences were found when comparing the performance of the two control schemes. On average, the ITCS control scheme was 1.15s faster than the EMG control scheme, corresponding to a 35.4% reduction in the activation time. The largest difference was for grasp 5 with a mean AT reduction of 45.3% (2.38s). The findings indicate that using the ITCS control scheme could allow for faster activation of specific grasps or functions compared with a conventional EMG control scheme. For transhumeral and especially bilateral amputees, the ITCS control scheme could have a significant impact on the prosthesis control. In addition, the ITCS would provide bilateral amputees with the additional advantage of environmental and computer control for which the ITCS was originally developed.

Boundary model predictive control of thin film thickness modelled by the Kuramoto–Sivashinsky equation with input and state constraints

In this work, a model modal predictive control (MMPC) strategy is proposed to stabilize the falling liquid film thickness in the vertical tubes modelled by the Kuramoto–Sivashinsky (K–S) equation in the presence of naturally present state and input constraints. The novel features of proposed synthesis is the development of an infinite dimensional PDE state representation which incorporates the exact transformation of boundary into the distributed control setting and benefits arising from the property of decoupled boundary applied input actuation and K–S PDE modal states. Furthermore, the dissipative structure of the K–S spectral operator provides the foundation for the model modal based predictive controller (MMPC) synthesis which utilizes the finite dimensional state representation to formulate the quadratic objective function while the infinite dimensional K–S PDE state constraints are appropriately defined and cast in the form of a constrained quadratic programme. Finally, we demonstrate that if feasible, the MMPC achieves stabilization of the thin film thickness and satisfies naturally present state and input constraints. Numerical simulation of the boundary applied actuation evaluates the proposed method's performance.

Feedback stabilisation of a two-dimensional pool-boiling system by modal control

The present study concerns the feedback stabilisation of the unstable equilibria of a two-dimensional nonlinear pool-boiling system with essentially heterogeneous temperature distributions in the fluid–heater interface. Regulation of such equilibria has great potential for application in, for instance, micro-electronics cooling. Here, as a first step, stabilisation of these equilibria is considered. To this end, a control law is designed that regulates the heat supply to the heater as a function of the Fourier–Chebyshev modes of its internal temperature distribution. These modes are intimately related to the physical eigenmodes of the system and thus admit robust and efficient regulation on the basis of the natural composition of the temperature field. Key to this modal-control strategy and its application for controller design are an interchangeable PDE form and state-space form of the linearised model. Derivation of these forms is a central theme of this study. Performance of modal controllers thus designed is demonstrated and analysed by simulations of the nonlinear closed-loop system.

Finite Element Analysis and Vibration Control of a Deep Composite Cylindrical Shell Using MFC Actuators

A four-node composite facet-shell element is developed, accounting for electromechanical coupling of Macrofiber Composite (MFC) and conventional PZT patches. Further a warping correction is included in order to capture correctly the induced strain of conformable MFC, surface bonded on a cylindrical shell. The element performance to model the relations between in-plane electric field to normal strains is examined with the help of experiment and ANSYS analysis. In ANSYS, a simple modeling scheme is proposed for MFC using a parallel capacitors concept. The independent modal space control technique has been revisited to address the control of combination resonances through a selective modal space control scheme, where two or more modes can be combined to form the vibrating system or plant in modal domain. The developed control schemes are implemented in a digital processor using DS1104 and the closed-loop vibration control experiments are conducted on a CFRP shell structure. The influence of directionally induced actuation of MFC actuators on elastic couplings of composite shell is studied theoretically and is subsequently demonstrated in experiments. MFC actuators provide the much needed optimization domain for achieving the vibration control of combination resonances of elastically coupled deep-shell structure.

Modal-based LQG for smart base isolation system design in seismic response control

This study presents a smart system design to enhance the seismic performance of base-isolated buildings using modal LQG control strategies and smart devices, magnetorheological dampers. The advantages of applying the modal LQG approach for base isolation are discussed, including the explicit physical interpretation, simple weighting selection, and easy controller order reduction. 2DOF base isolation systems and the well-known, community-driven, benchmark base isolation problem focusing on structural control are employed to demonstrate the technique as realistic examples. This study analyzes the underlying interaction between structural dynamic properties and control forces that makes the modal approach effective and smart base isolation control possible and shows the seismic performance gain of the benchmark base isolation system offered by the proposed approach. Copyright © 2012 John Wiley & Sons, Ltd.

Dynamic modeling and H ∞ independent modal space vibration control of laminate plates

In this paper, combining the transfer matrix method and the finite element method, the modified finite element transfer matrix method is presented for high efficient dynamic modeling of laminated plates. Then, by constructing the modal filter and the disturbance force observer, and using the feedback and feedforward approaches, the H ∞ independent modal space control strategy is designed for active vibration control of laminate plates subjected to arbitrary, immeasurable disturbance forces. Compared with ordinary dynamic modeling and control methods of laminated plate structures, the proposed method has the low memory requirement, high computational efficiency and robust control performance. Formulations as well as some numerical examples are given to validate the method and the control performance.

Active Control and Energy Cost Assessment of a Rotating Machine

The performances for controlling a rotating machine by using either an Electromagnetic Actuator or a Piezoelectric Actuator are compared in this work. The aim is to establish selection criteria based on environmental impact. Life Cycle Analysis shows that the operating stage has a considerable impact. In this study, only the operating stage is considered. The energy consumed by the actuators seems to be the appropriate indicator for the same "mechanical" performances. Numerical studies are carried out in order to quantify the energy consumed in each case. Modal control strategy with a fuzzy controller is used. The controller inputs are displacements and velocities. The system studied is modeled by using finite element method and the electrical circuit of each actuator is modeled by using basic electricity and electromagnetism theories. Several configurations are assessed and defined by using the chosen Functional Unit.The results obtained show that both controllers are efficient and enable recommendations for optimal control procedures design for the energy consumed.

Active Control and Energy Cost Assessment of Rotating Machine

The performances for controlling a rotating machine by using either an Electromagnetic Actuator or a Piezoelectric Actuator are compared in this work. The aim is to establish selection criteria based on environmental impact. Life Cycle Analysis shows that the operating stage has a considerable impact. In this study, only the operating stage is considered. The energy consumed by the actuators seems to be the appropriate indicator for the same mechanical performances. Numerical studies are carried out in order to quantify the energy consumed in each case. Modal control strategy with a fuzzy controller is used. The controller inputs are displacements and velocities. The system studied is modeled by using finite element method and the electrical circuit of each actuator is modeled by using basic electricity and electromagnetism theories. Several configurations are assessed and defined by using the chosen Functional Unit.The results obtained show that both controllers are efficient and enable recommendations for optimal control procedures design for the energy consumed.

Control of semi-active anti-roll systems on heavy vehicles

Semi-active anti-roll systems, with a high and low roll stiffness, or, since cornering is typically a transient event, damping setting have the capacity to improve heavy vehicle stability while having very low power consumption. If a vehicle is travelling around a right-hand bend and a low roll damping setting is selected, the vehicle will roll outwards. If a high damping setting is then selected, the outward roll will be locked-in. When the vehicle enters a left-hand bend, the inward roll becomes locked-in. This has the potential to increase critical lateral acceleration by up to 12.5% if the vehicle's future course can be predicted accurately (e.g. with a Global Positioning System). However, if the vehicle does not follow the expected path, the critical lateral acceleration may be degraded. Exploiting the delay between a steer angle being applied and the lateral acceleration developing could avoid this problem. However, the benefits from such a system are considerably lower, up to a 2.4% improvement in critical lateral acceleration. Hence, a ‘modal control strategy’ is developed aimed at providing high levels of benefit while being robust to deviations from the expected path. The modal strategy is able to provide benefits of up to 11%, while being robust to most deviations.

MULTI-MODE VIBRATION CONTROL AND POSITION ERROR ANALYSIS OF PARALLEL MANIPULATOR WITH MULTIPLE FLEXIBLE LINKS

This paper presents multi-mode vibration control and analysis of moving platform position errors of a planar 3-PRR parallel manipulator with three flexible intermediate links using PZT transducers. The active vibration controller is designed in modal space with modal filters and modal synthesizers determined from the flexible link vibration characteristics. Estimation of the moving platform position error is conducted using measurements of the flexible link deflection from PZT sensors mounted on the flexible intermediate links. An effective strategy for determining the control gains to reduce the vibrations of higher order modes is proposed through modification of the independent modal space control (IMSC) method. The proposed independent modal control strategy is experimentally implemented with first two modes targeted for control on a parallel manipulator with multiple flexible links. The experimental results show that the vibrations of the first two modes are effectively suppressed, and the position error of the moving platform is substantially reduced.

A semi-analytical method and the circumferential dominant modal control of circularcylindrical shells with active constrained layer damping treatment

To enhance the generality and flexibility of active constrained layer damped (ACLD) formsused in vibration control for circular cylindrical shells, the piezoelectric layer of the ACLDform is divided into several sub-blocks by thin insulated layers, and the sub-blocks areintegrated on the viscoelastic layer continuously in the circumferential direction. Inaddition, on the basis of the authors’ recent research on passive constrained layerdamped (PCLD) circular cylindrical shells, the piezoelectric effects of the constrained layer(made of piezoelectric material) are further considered. Then, the integrated first-orderdifferential equation for such an ACLD (partially treated in the axial direction) circularcylindrical shell is derived by reformulating the integrated first-order differentialequation for the PCLD circular cylindrical shell. Next, employing the extendedhomogeneous capacity precision integration approach and the superposition principle,a high precision semi-analytical method is developed for solving the dynamicproblem for such ACLD circular cylindrical shells. Subsequently, several kinds ofcircumferential modal control strategy are compared by the method presented.Furthermore, the concept of a circumferential dominant modal control strategyis proposed, which is different from the traditional modal control method. Thenumerical results show that, on applying the circumferential dominant modalcontrol strategy, the ACLD cylindrical shell attenuates the vibration better. Lastly,some influence factors for the circumferential dominant modal control strategyaffecting the damping effect of ACLD circular cylindrical shells are also investigated.

Semi-adaptive modal control of on-board electronic boards using an identificationmethod

Modal active control, based on a state model, is an efficient method of increasing thelifetime of electronic boards by using piezoelectric components. In the case of industrialmass production, dispersions lead to changes in mechanical and electromechanicalproperties. Moreover, initial operating conditions such as boundary conditions can changeduring the lifetime of the control and modify its efficiency and stability. Therefore, asemi-adaptive modal control strategy in deferred time is proposed to attenuate theseproblems. Firstly modal control gains are calculated by using a classical linear quadraticGaussian algorithm with the nominal model including mode shapes. Then control I/Odata are collected by an identification system that uses on-board piezoelectriccomponents. A subspace method is implemented to estimate modal matrices in order toupdate the controller. The sensitivity of control performance to modal parametervariation is presented. Estimated control frequencies and modal damping are finallyused to update modal control gains. The effectiveness of the proposed method isexamined through numerical simulation and experimental tests in the case ofboundary condition modifications. This adaptive modal control/identification designgreatly increases the nominal robustness of the controller in the case of frequencyshifts.

On modal energy in civil structural control

A new control strategy based on modal energy criterion is proposed to demonstrate the effectiveness of the control system in reducing structural earthquake responses. The modal control algorithm combining LQR (linear quadratic regulator) control algorithm is adopted in the discrete time-history analysis. The various modal energy forms are derived by definition of the generalized absolute displacement vector. A preliminary numerical study of the effectiveness of this control strategy is carried out on a 20-storey framed steel structural model. The controlled performance of the model is studied from the perspectives of both response and modal energy. Results show that the modal energy-based control strategy is very effective in reducing structural responses as well as in consuming a large amount of modal energy, while augmentation of additional generalized control force corresponding to the modes that contain little modal energy is unnecessary, as it does little help to improve the controlled structural performance.

Modal Active Vibration Control of a Rotor Using Piezoelectric Stack Actuators

This work deals with active vibration control of a rotating machine in both steady state and transient motion. Two stacks of piezoelectric ceramic orthogonally arranged in a plane localized at one of the bearings were used as the control actuators, using a modal control strategy. The optimal controller LQR was used to calculate the control gain, working together with an LQE observer that estimates the modal state. Simulation carried out on FEM model suggested the feasibility of the control strategy, and experimental tests using a physical test rig show good agreement with the numerical results, and confirm the efficiency of the strategy.

An Efficient Modal Control Strategy for the Active Vibration Control of a Truss Structure

In this paper an efficient modal control strategy is described for the active vibration control of a truss structure. In this approach, a feedback force is applied to each mode to be controlled according to a weighting factor that is determined by assessing how much each mode is excited by the primary source. The strategy is effective provided that the primary source is at a fixed position on the structure, and that the source is stationary in the statistical sense. To test the effectiveness of the control strategy it is compared with an alternative, established approach namely, Independent Modal Space Control (IMSC). Numerical simulations show that with the new strategy it is possible to significantly reduce the control effort required, with a minimal reduction in control performance.