Journal of Vibration and Control current issue

Vibration Control on a Pulse and Ramp Driven System with Friction

Shyu, K.-K., Lee, Y.-Y., Wu, R.-H. — Tue, 24 Nov 2009 03:29:17 PST

This paper investigates the sufficient stability condition of a three-phase proportional gain, pulse, and ramp (PPR) controller for pointing systems under the influence of friction. With the ramp and pulse schemes integrated, the PPR controller has been demonstrated to be an effective control strategy for fast and precise pointing applications. In this paper the LuGre model is used to derive the upper bounds of the ramp slope S_r for the sufficient stability condition to suppress vibrations around the [—0.5, +0.5] µm target region. Our study reveals that the frictional stiffness ₀ and the micro viscous damping coefficient ₁ in the LuGre model are required for the bounds of S_r . With the derived bounds of S_r , the Lyapunov direct method is applied to prove the stability of the PPR controller.

General-order Perturbation with a Skew-symmetric Approach for Structural Health Monitoring of a Modular Beam

Wong, C. N., Barhorst, A. A. — Tue, 24 Nov 2009 03:29:17 PST

A unique health monitoring method is formulated via a skew-symmetric approach in which the damage location and extent are estimated from the perturbation of a specific set of eigenparameters. The perturbed orthonormal equation is generated from the perturbation of the eigenvectors and eigenvalues to obtain the kth skew-symmetric coefficients. Meanwhile the perturbed eigenvalue equation is generated from the perturbation of the eigenparameters and linear expansion of the stiffness matrix to obtain other skew-symmetric coefficients. Throughout this process, specific permutation numbers and generalized Kronecker delta functions are manipulated. Then these skew-symmetric coefficients are simplified to obtain the symmetric coefficients. A finite element model of a modular beam is used as a test structure to investigate the applicability of the developed method. A fixed—fixed boundary condition is imposed on the two ends to approximate the actual operating situation. Different order perturbation algorithms are established based on the perturbation equations. Stiffness parameters are computed from these equations, inversely, using an optimization method. The algorithm is iterative in nature and terminates under certain criteria. Various small to large percentage systematic damaged cases are simulated under different perturbation orders. The results are compared and evaluated using health monitoring curves and estimation error manifolds, and their efficiencies and convergences are discussed.

Development of Adaptive Seat Mounts for Helicopter Aircrew Body Vibration Reduction

Chen, Y., Wickramasinghe, V., Zimcik, D. — Tue, 24 Nov 2009 03:29:17 PST

Helicopter aircrew are exposed to high levels of vibration and noise during flight. This paper presents the investigation of adaptive seat mount approaches to reducing vibration on the helicopter seat. A flight test on a helicopter with typical pilot configurations showed that the vibration spectra on the pilot’s helmet not only included the dominant N/rev harmonic peaks of the rotor speed, but also consisted of a low-frequency resonant peak in the frequency range of human abdominal and spine resonant frequencies. Long-term exposure to this vibration may lead to occupational health issues such as damage to the pilot’s spine and neck. In order to address this issue, a novel adaptive seat mount concept was developed to mitigate the vibration levels transmitted to the aircrew. As a proof-of-concept demonstration, a miniature modal shaker was installed between the cabin floor and the seat bottom as an adaptive mount that provided the actuation authority. The objective was to reduce the vertical vibration transmitted to the aircrew helmet in order to decrease aircrew neck and spine injuries that are caused by the transmitted vibration. Extensive closed-loop control tests have been conducted on a full-scale helicopter seat and a mannequin with varying physical properties. A 10,000 lb(f) mechanical shaker was used to provide representative helicopter vibration profiles to the seat. Significant vibration reductions on the N/rev vibration peaks were achieved1 the low-frequency resonant peak was also suppressed simultaneously.

Localization in the Vibration of an Axially Loaded Two-span Weakened Column

Challamel, N., Casandjian, C., Lanos, C. — Tue, 24 Nov 2009 03:29:17 PST

This paper is devoted to the dynamic analysis of two connected beam columns with a variation of the bending connection and minor perturbations of the length of each span. The point of reduced bending stiffness represented by a rotational spring may result from a crack. This rotational spring can also be associated with a semi-rigid connection in the field of steel or composite structures, for instance. The dynamics of this axially loaded two-span weakened column appears to exhibit strong localization for small values of stiffness of the rotational spring. The vibration mode shapes indicate a strong confinement of the vibration level to a fraction of the column. A quantitative criterion of localization is established and is correlated to well-known phenomena such as curve veering effect or close eigenvalues. Such a result is quite encouraging as localization is strongly associated with the flexibility values of the rotational spring. When considering the open crack analogy, localization only appears for severely damaged columns. It can then be understood as an indicator of the damage level of the global structure.

An Improved System of Active Noise Isolation Using a Self-sensing Actuator and Neural Network

Ji, H., Qiu, J., Zhu, K., Matsuta, K. — Tue, 24 Nov 2009 03:29:17 PST

In this paper we present an improved active noise isolation method, consisting of a self-sensing actuator, a neural network identifier and an adaptive feedback controller using a finite impulse response (FIR) filter and the Filtered-X LMS algorithm, in which no acoustical sensors were necessary to suppress the noise transmission through a plate structure. The structure is a composite plate with an embedded piezoelectric patch. Based on the self-sensing technique, the same piezoelectric element functions as both a sensor and an actuator. A bridge circuit was used to separate the sensor signal from the actuator signal on the piezoelectric patch and the obtained signal was used in the identification of the sound pressure of a point in the space. A neural network was used instead of the Rayleigh’s integral formula for the identification of the sound pressure as used in the former study. The results show that the proposed control approach using both a self-sensing actuator (SSA) and neural network identifier exhibited better noise control performance than using Rayleigh’s integral formula. It also exhibited similar noise control performance to the traditional control system using a microphone, although the new system used only one piezoelectric patch for both the sensor and actuator.

Simple Approaches to Improve the Performance of Noise Cancellation

Chang, C.-Y. — Tue, 24 Nov 2009 03:29:17 PST

In this paper we present a neural-based algorithm to cancel the nonlinear narrowband and broadband noise in an active noise control (ANC) system. The improved method, including the ways to decide the learning rate and optimal initial weighting values of the neural network (NN), are presented to enhance the noise reduction performance. The proposed approach does not need mathematical transfer functions of the duct plant and a method of avoiding the premature saturation problem of NNs is also provided. A comparison with conventional neural methods by simulation shows that the proposed method can effectively cancel the undesired noise very well. The proposed improved method is also versatile to the other applications in NN filter design.

Vibration Suppression Control of Beam-cart System with Piezoelectric Transducers by Decomposed Parallel Adaptive Neuro-fuzzy Control

Lin, J., Chao, W.-S. — Tue, 24 Nov 2009 03:29:17 PST

The main goal of this research is to develop a novel approach for achieving a high performance piezoelectric vibration absorber. Motion and control of a Bernoulli-Euler beam fixed on a moving cart will be analyzed in this study. The moving cart is mounted on the ball-screw mechanism system. Dynamic formulation for control purposes is first investigated for such a beam-cart system in this research. The controller has two separate feedback loops for positioning and damping, and the vibration suppression controller is independent of linear motion stage positioning control. The decomposed parallel fuzzy control with adaptive neuro-fuzzy concept has also been proposed for this research. An experimental device was constructed, constituted of a flexible cantilever aluminum beam type structure with piezoelectric patches symmetrically bonded on both sides to provide structural bending. Strip-bender type piezoelectric patches were attached to the surface of the beam to serve as actuators and sensor, respectively. Experimental validation for such a structure demonstrates the effectiveness of the proposed controller. The results of this study can be feasible to various mechanical systems, such as high tower cranes, ladder cars or overhead cranes.

An Intelligent Controller Design for Magnetorheological Damper Based on a Quarter-car Model

Tusset, A. M., Rafikov, M., Balthazar, J. M. — Tue, 24 Nov 2009 03:29:17 PST

This paper presents the control strategies of nonlinear vehicle suspension using a magnetorheological (MR) damper. We used two different approaches for modeling and control of the mechanical and electrical parts of the suspension systems with the MR damper. First, we have formulated and resolved the control problem in order to design the linear feedback dumping force controller for a nonlinear suspension system. Then the values of the control dumping force functions were transformed into electrical control signals by the application of a fuzzy logic control method. The numerical simulations were provided in order to show the effectiveness of this method for the semi-active control of the quarter-car suspension.