Active Vibration Damping Research Articles

Variable structure maneuvering control with time-varying sliding surface and active vibration damping of flexible spacecraft with input saturation

This paper presents a dual-stage control system design method for the three-axis-rotational maneuver and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensors/actuators. In this design approach, attitude control system and vibration suppression were designed separately using lower order model. The design of attitude controller was based on variable-structure control (VSC) theory leading to a discontinuous control law. To accomplish asymptotic attitude maneuvering in the closed-loop system and be insensitive to the interaction of elastic modes in the presence of unknown disturbances/uncertainty and input saturation as well, a switching mechanism is employed to design the attitude controller such that outside the sliding region VSC law with a time-varying sliding surface is implemented and inside the region the VSC law with a linear sliding surface is activated. Furthermore, a hyperbolic tangent function in conjunction with a sharpness function permitted to vary with time according to a set of user-defined parameters is implemented to offset the disadvantages of existing saturation-respecting controller and chattering. In addition, for actively damping the excited elastic vibrations during attitude maneuvering, modal velocity feedback and strain rate feedback control design methods are presented and compared by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque, parameter uncertainty and control saturation nonlinearity.

Basic equations for thermoviscoelastic plates with distributed actuators under monoharmonic loading

The basic equations for thin-walled thermoviscoelastic plates with distributed piezoelectric actuators under monoharmonic mechanical and electric loads are derived. The thermomechanical behavior of materials is described using the concept of complex characteristics. Variational methods of solving nonlinear problems of active damping of the bending vibrations of plates are considered. The effect of dissipative heating on the damping of the axisymmetric bending vibrations of a circular plate is examined as an example

Self-diagnosis of smart structures based on dynamical properties

When we talk about “smart structures” we can think about different properties and capabilities which make a structure “intelligent” in a certain sense. Originally, the expression “smart” was used in the context that a structure can react and adapt to certain environmental conditions, such as change of shape, compensation of deformations, active vibration damping, etc. Over the last year, the expression “smart” has been extended to the field of structural health monitoring (SHM), where sensor networks, actuators and computational capabilities are used to enable a structure to perform a self-diagnosis with the goal that this structure can release early warnings about a critical health state, locate and classify damage or even to forecast the remaining life-time. This paper intends to give an overview and point out recent developments of vibration-based methods for SHM. All these methods have in common that a structural change due to a damage results in a more or less significant change of the dynamic behavior. For the diagnosis an inverse problem has to be solved. We discuss the use of modal information as well as the direct use of forced and ambient vibrations in the time and frequency domain. Examples from civil and aerospace engineering as well as off-shore wind energy plants show the applicability of these methods.

Design of Delayed Reference Controllers for Simultaneous Path Tracking and Active Vibration Damping of Multi-degree-of-freedom Linear Systems

This paper presents an innovative non-time-based control strategy for the simultaneous path tracking and active vibration damping of multi-degree-of-freedom linear systems. The fundamental difference between the proposed scheme, and those that have already appeared in literature, is that it allows keeping the coordinated motion of different actuators. In other words, the use of such a scheme guarantees that a desired path in space is accurately followed while suppressing the undesired vibrational effects. The control strategy consists in actively suppressing the undesired vibrations by suitably changing the path reference for the system. Such a result can be achieved by making the path reference for the system be a function of an action reference parameter rather than just the time. The reference parameter depends on time and on a variable which plays the role of a time delay. The latter is computed on the fly, on the basis of the measured vibration. A cascade control structure is obtained, where no specific position controllers or actuators are to be employed in the inner loop.The theory developed is demonstrated through numerical simulations by applying it to the vibration and path tracking control of a four-degrees-of-freedom two-mass system.

Frequency Domain Identification of the Active Beam Model for the Vibration Control System

An identification procedure of the active vibration damping system with the piezo-elements glued to the structure is presented in the paper. Such identification can be carried out in analytical way (Guyan reduction) by using of low-band pass amplifiers. First, we have identified the open loop system in the frequency domain by using experimental setup with real amplifier and beam equipped in piezo-strips working as actuators and sensor, respectively. For the frequency range 1 Hz to 400 Hz we have obtained Bode plots with helped of Dynamic Signal Analyzer which were base to further calculations. Second, mathematical model have been adjusted to the experimental results by the least square sum approach and also by the consideration of a system which was modeled by finite elements. A three first resonance frequencies and three first anti-resonance frequencies have obtained.

Active Vibration Damping for an Off-Road Vehicle with Displacement Controlled Actuators

AbstractMobile earthmoving machines typically do not have wheel suspension. Consequently, vehicle dynamics are under-damped, and operators experience vibrations of low frequency and high amplitude which are detrimental to health, comfort and productivity. For most vehicles, the state of the art for improving ride quality is passive energy dissipation via seat dampers and hydraulic accumulators connected in parallel to the actuators. Alternatively, ride quality may be enhanced by active control of the seat or working actuators. In the present work, active vibration damping is considered for a skid-steer loader based on control of the flow rate to the boom lift cylinders with a variable displacement pump. A four degrees of freedom vehicle dynamic model is derived for linear motion in the vertical and horizontal directions, pitching angle, and boom motion with respect to the chassis. Dynamics of the hydraulic pump and actuator are also modelled. Considering the requirements of the intended application, the f...

Tunable vibration absorption device

A tunable vibration absorption device is provided that is suitable for active or semi-active vibration absorption or damping of vibrations in vibrating structures. It comprises a stack including a force actuator mechanism for generating an axial actuation force and a force sensor mechanism which is responsive to an external force acting on the stack to generate a force signal. A controller unit is electrically connected to the force sensor mechanism for receiving the force signal generated by the force sensor mechanism, and it is also electrically connected to the force actuator mechanism for adjusting the axial actuation force generated by the force actuator mechanism in response to the received force signal generated by the force sensor mechanism.

Active vibration damping system

A system (100, 200, 300) for damping vibrations of a vibratory structure (104, 308). The damping system includes an active damper (112, 124, 128, 216), a vibration sensor (116, 208, 208A′-C′), and a controller (120, 212) for controlling the active damper in a manner that damps vibration of the vibratory structure. In some embodiments, the active damper comprises an active mass (132, 220, 220A′-C′, 220A″-C″) and an actuator (136) for controlling the movement of the active mass. In other embodiments, the active damper comprises a flexural damper (128).

Active Vibration Damping and Model‐Based Control for an Adaptronic Actuator

AbstractThe static and dynamic flexibility of a machine tool is often the major limiting factor for the machining quality, especially if high processing speeds as well as high accuracies are desired. Particularly parallel kinematic machines, which have been developed for high processing speeds and accuracy and which often use lightweight structures, can suffer from severe problems with vibrations of system components and the loss of accuracy due to deformations of machine parts. Introducing so–called adaptronic or smart components into the machine tool structure opens up new and interesting possibilities to actively control the deformations and vibrations of flexible machine parts. They allow to specifically target such undesired properties and to significantly reduce or even eliminate their influence on the system performance. Concepts of active vibration damping and model–based control are presented here for such an adaptronic actuator implemented in a machine tool with parallel kinematics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Wave-based control of non-linear flexible mechanical systems

The need to achieve rapid and accurate position control of a system end-point by an actuator working through a flexible system arises frequently, in cases from space structures to disk drive heads, from medical mechanisms to long-arm manipulators, from cranes to special robots. The system’s actuator must then attempt to reconcile two, potentially conflicting, demands: position control and active vibration damping. Somehow each must be achieved while respecting the other’s requirements. Wave-based control is a powerful solution with many advantages over previous techniques. The central idea is to consider the actuator motion as launching mechanical waves into the flexible system while simultaneously absorbing returning waves. This simple, intuitive idea leads to robust, generic, highly efficient, adaptable controllers, allowing rapid and almost vibrationless re-positioning of the remote load (tip mass). This gives a generic, high-performance solution to this important problem that does not depend on an accurate system model or near-ideal actuator behaviour. At first sight wave-based control assumes superposition and therefore linearity. This paper shows that wave-based control is also robust (or can easily be made robust) to non-linear behaviour associated with non-linear elasticity and with large-deflection effects.

Modeling of Beam as Control Plane for a Vibration Control System

An active vibration damping system with the use of piezoelements fixed to the structure is presented in the paper. The optimal location of the piezo-stripes on the structure is calculated for given cost functions. Coefficient correlations between control forces, strains, mode shapes, frequency changes, modal masses and modal stiffness are analyzed in order to find simpler method for calculation of the quasi-optimal localization of piezo-sensors and piezo-actuators. Reduced model of the open-loop system was identified and the simulations were carried out in order to find the best controller to reduce the amplitude of vibrations. The correctness of the selection of the controller was verified and investigated experimentally.

The influence of dissipative heating on active vibration damping of viscoelastic plates

A mathematical formulation of a new nonlinear problem for active vibration damping (ACD) of thin viscoelastic plates by distributed piezoelectric sensors and actuators is given. The influence of dissipative heating on ACD is considered. The nonlinearity of the problem is caused by the temperature dependence of the material properties and the nonlinearity of the dissipative function. The thermomechanical behavior of the materials under harmonic loading is described by the concept of complex characteristics. Numerical and analytical methods are used for solving this problem. As an example, the influence of dissipative heating on damped axisymmetric bending vibrations of a circular viscoelastic plate is investigated. It is shown that this influence can be significant in the case of ACD of polymeric plates.

Damping the vibrations of a rectangular plate with piezoelectric actuators

The paper addresses the active damping of nonstationary vibrations of a hinged rectangular plate with distributed piezoelectric actuators. The problem is solved by two methods: (i) the classical method of balancing the fundamental vibration modes by applying the appropriate potential difference to the actuator and (ii) the dynamic-programming method that reduces the problem to an algebraic Riccati equation. The results produced by both approaches are presented and compared

Vibration Damping of a Flexible Car Body Structure Using Piezo-Stack Actuators

In this work piezo-stack actuators mounted in consoles are utilized to actively dampen vibrations of a flexible car body structure by introducing bending moments. Using an example of a heavy metro vehicle the complete design for the active vibration damping system is presented. Both analytical modeling and a system identification of the vehicle are described, issues of modal representation and model reduction are covered, and a robust controller design is motivated and explained. The excellent performance of the proposed method is documented by both experimental results from a scaled model and an extensive co-simulation of the overall system.

The DLR lightweight robot: design and control concepts for robots in human environments

PurposeThe paper seeks to present a new generation of torque‐controlled light‐weight robots (LWR) developed at the Institute of Robotics and Mechatronics of the German Aerospace Center.Design/methodology/approachAn integrated mechatronic design approach for LWR is presented. Owing to the partially unknown properties of the environment, robustness of planning and control with respect to environmental variations is crucial. Robustness is achieved in this context through sensor redundancy and passivity‐based control. In the DLR root concept, joint torque sensing plays a central role.FindingsIn order to act in unstructured environments and interact with humans, the robots have design features and control/software functionalities which distinguish them from classical robots, such as: load‐to‐weight ratio of 1:1, torque sensing in the joints, active vibration damping, sensitive collision detection, compliant control on joint and Cartesian level.Practical implicationsThe DLR robots are excellent research platforms for experimentation of advanced robotics algorithms. Space and medical robotics are further areas for which these robots were designed and hopefully will be applied within the next years. Potential industrial application fields are the fast automatic assembly as well as manufacturing activities done in cooperation with humans (industrial robot assistant). The described functionalities are of course highly relevant also for the potentially huge market of service robotics. The LWR technology was transferred to KUKA Roboter GmbH, which will bring the first arms on the market in the near future.Originality/valueThis paper introduces a new type of LWR with torque sensing in each joint and describes a consistent approach for using these sensors for manipulation in human environments. To the best of one's knowledge, the first systematic experimental evaluation of possible injuries during robot‐human crashes using standardized testing facilities is presented.

Sliding mode maneuvering control and active vibration damping of three-axis stabilized flexible spacecraft with actuator dynamics

This paper presents a dual-stage control system design method for the three-axis-rotational maneuver control and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator. In this design approach, the attitude control system and vibration suppression were designed separately using a lower order model. Based on the sliding mode control (SMC) theory, a discontinuous attitude control law in the form of the input voltage of the reaction wheel is derived to control the orientation of the spacecraft actuated by the reaction wheel, in which the reaction wheel dynamics is also considered from the real applications point of view. The asymptotic stability is shown using Lyapunov analysis. Furthermore, an adaptive version of the proposed attitude control law is also designed for adapting the unknown upper bounds of the lumped disturbance so that the limitation of knowing the bound of the disturbance in advance is released. In addition, the concept of varying the width of boundary layer instead of a fixed one is also employed to eliminate the chattering and improve the pointing precision as well. For actively suppressing the induced vibration, modal velocity feedback and strain rate feedback control methods are presented and compared by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque and parameter uncertainty.

Active damping of forced vibrations in a two-mass system using force and parametric effects

A linear dynamic model of two masses sequentially connected with linear elastic links is considered. The masses are under the effect of external harmonic perturbations that have the same frequency but differ by amplitude; there is also a phase difference between the forces. To decrease the intensity of forced vibrations, two vibration-damping factors are activated: a force applied to one of the mass and a parametric factor corresponding to periodic changes in rigidity of the mass fixing. The structure of quasi-optimal vibration-suppression laws ensuring the minimal amplitude of steady-state vibration is determined in a closed form.

Variable structure attitude manoeuvre control and active vibration damping of three-axis-stabilized flexible spacecraft

This paper presents a dual-stage control system design method for the three-axis-rotational manoeuvre and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as the sensor and actuator. In this design approach, the attitude control system and vibration suppression were designed separately using a lower-order model. The design of the attitude controller was based on the variable structure control (VSC) theory, leading to a discontinuous control law. This controller accomplishes asymptotic attitude maneouvring in the closed-loop system and is insensitive to the interaction of elastic modes and uncertainty in the system. The advantage of this dual-stage approach is that once the desired orientation is attained under the VSC law, only the elastic motion is governed by the decoupled linear second-order systems describing elastic dynamics. To this end, modal velocity feedback and optimal positive position feedback control methods are presented and compared for actively damping the elastic oscillations using piezoelectric materials as an additional sensor and actuator bonded on the surface of the flexible appendages. In addition, a special configuration of actuators for three-axis attitude control is also investigated: the pitch attitude controlled by a momentum wheel and the roll/yaw control achieved by on-off thrusters, which is modulated by the pulse width-pulse frequency modulation technique to construct a proper control torque history. Numerical simulations are performed to show that the rotational manoeuvre and vibration suppression are accomplished in spite of the presence of disturbance torque and parameter uncertainty.

Active electromagnetic damping of laterally vibrating ferromagnetic cantilever beam

In linear mechanical systems, the vibration of mechanical structures depends upon the boundary conditions, the mode of excitation and the dissipative or damping capacities of the system itself. The latter are the result of passive residual and structural friction. In the cases where passive damping of mechanical structures becomes inadequate, dynamic reactivity of the structure may be influenced by controlled active damping which is particularly suitable for non-linear systems where the structure response and excitation are directly interconnected. The present paper deals with active electromagnetic damping of lateral vibration of a clamped steel cantilever. The electromagnetic system consists of a switching current amplifier and a pair of electromagnets, which are mounted laterally at a right angle to the plane of the steel cantilever. A simulation model of control system has been produced and confirmed by experiments. Control algorithm is simple, efficient and ensures stability in operation.

Adaptronic Vibration Damping for Machine Tools

A newly designed adaptronic component with a powerful piezo-stack actuator for active damping of machine vibrations is presented in this paper. Especially for machine tools with parallel kinematics, which feature lightweight structures and which are built in order to obtain high processing speeds, the active damping of machine vibrations is important to achieve the desired system performance. Extensive simulation studies with flexible multibody systems in order to test different control algorithms such as dissipative control, integrated force feedback or H 2/H ∞ control and recent experimental results show the high potential to improve the system behavior.