Paul Sas

Towards a mechatronic compiler

A simultaneous engineering framework for designing optimal mechatronic systems is presented. In the first part of this paper, a method, based on genetic algorithms, for optimizing the geometric configuration of three-axis machine tools in the conceptual design stage is presented. The second part describes a method, based on component mode synthesis, to derive a low-order control model from a finite-element description of the mechanical and drive structures of the mechatronic system. In the third part, motion controllers are derived that are robust against configuration changes of the mechatronic system to be controlled.

Vibro‐acoustical modal analysis: Reciprocity, model symmetry, and model validity

For low‐frequency applications, a modal approach can be useful to describe vibro‐acoustical coupling. Based on combined vibrational/acoustical frequency response function measurements, either with respect to acoustical or structural excitation, modal vibro‐acoustical analysis can be carried out. This paper presents a consolidation of the theory behind the vibro‐acoustical modal model. The model formulation is shown to be a nonsymmetrical formulation. It is shown that this is not contradictory to the well‐known vibro‐acoustical reciprocity principle. The implications of the nonsymmetry for the modal model are discussed. It is pointed out which variables must be measured and what kind of scaling must be used in order to end up with a consistent modal formulation. The theory is illustrated and verified by measurements on an experimental vibro‐acoustical system, consisting of a rigid cavity with one flexible wall.

STATISTICAL ANALYSIS OF THE POWER INJECTION METHOD

The power injection method (PIM) has become widely accepted as a valuable technique to predict the statistical energy analysis (SEA) parameters of a structure in situ. PIM requires the measurement of the power input into every single subsystem and the measurement of the energy level of every subsystem. By inverting the appropriate measured energy matrix, the SEA parameters can be obtained. Conventional PIM suggests to use a more or less predefined number of excitation and response locations. Most often three excitation and five response locations are taken. Due to the spatial variation of the energy density in a subsystem, there will always be a substantial variability associated with the space‐averaged energy of vibration and hence associated with the SEA parameters. An accurate SEA model requires accurately measured space averaged energies of vibration and power input levels. The accuracy of the SEA parameters can be assessed by evaluating the confidence levels of the so‐called ‘‘normalized energy level...

Active Control of Structure-Borne Road Noise Using Vibration Actuators

Structure-borne road noise is generated by road induced excitation forces. The control approach presented here relies on the use of vibration actuators to modify the vibration behavior of the car body such that its noise radiation efficiency is decreased (Active Structural Acoustic Control-ASAC). The controller is optimized using laboratory experiments and numerical tools to simulate the performance a complete vehicle control set-up. Road tests yield a 6.9 dB noise reduction in the frequency range 75-105 Hz at the error microphone and 6.1 dB noise reduction at the passengers ear.

Optimal decoupling for improved multivariable controller design, applied on an automotive vibration test rig

Within the framework of tracking controller design for an automotive vibration test rig, a new control strategy is developed which is applicable to square multiple-input-multiple-output systems (MIMO-systems) with a certain degree of symmetry. Classical MIMO-controller design is a three step procedure: response measurement, MIMO-identification and MIMO-controller design. The latter two steps are often very cumbersome due to the multivariable character of the problem. In. this paper, a new procedure is proposed which replaces the second step with: (1) almost decoupling of the MIMO-system into multiple single-input-single-output systems (SISO-systems) by transformations of the inputs and the outputs; and (2) SISO-identifications of the decoupled systems. Thereby simplifying the control-design step to multiple SISO-controller designs. This paper also discusses the successful application of this new procedure on an industrial automotive vibration test rig.

Machine Condition Monitoring Using Signal Classification Techniques

Two signal classification approaches, based on Wigner-Ville distribution and extended symmetric Itakura distance, are proposed to post-process the time-frequency representations (TFRs) of vibration signatures, with the final aim to arrive at an automated procedure of machine condition monitoring. Three synthetical signals are used to evaluate and compare the classification performance of these techniques. Some related computation issues, such as characters of different TFRs and weighted window length, are discussed. Experimental case studies, joint fault diagnosis, are realized.

Fault Diagnosis of Joint Backlash

The aim of this paper is to develop appropriate techniques to detect and classify the joint backlash ofa robot by monitoring its vibration response during normal operating conditions. In this investigation, Wigner-Ville distributions combined with two-dimensional correlation techniques have been employed to diagnose the joint faults of multi-link robots. In the study reported here, signal detection based on the Wigner-Ville distribution is proposed as a tool for pattern differentiation. To evaluate the performance of different detection procedures, the detection ofa simulated impact transient embedded in three simulated observed signals is presented. To assess the validity of the proposed approaches, they have been successfully employed in the fault diagnosis of link-joints on both a two-link mechanism and an industrial robot.

Optimization methods for choosing sensor and actuator locations in an actively controlled double-panel partition

The present study addresses the optimization of the locations of the error sensors and the control actuators in an active noise control system. This system is implemented on a double- panel partition in order to improve its sound insulation characteristics in the low frequency range. A model of the active control system, allowing both structural and acoustical control, is developed and combined with a finite element model of the double-panel partition. This yields a discrete description of the actively controlled structure, resulting in a combinatorial optimization problem. As the optimal solution for this problem can only be found by enumeration, a genetic algorithm is generally used to generate a near-optimum solution, requiring however a lot of useless function evaluations. In order to overcome this severe drawback of the genetic algorithm a number of non-linear optimization methods are also tested. As these methods can only handle continuous problems, interpolating functions are used to approximate the dynamic behavior of the structure in between the finite element nodes. Finally the performances of the methods are compared in terms of quality of the obtained solution, computation time and algorithm complexity. This comparison shows that the best gradient method converges faster and yields a better final solution than the best genetic algorithm.

Dynamic Analysis of Flexible Structures Using Component Mode Synthesis

In this paper a dynamic model of a flexible robot is built out of a finite element model of each of its links. The number of degrees-of-freedom of these models is strongly reduced by applying the Component Mode Synthesis technique which involves the preliminary calculation of a limited number of mode shapes of the separate links. As can be seen from examples, the type of boundary conditions thereby imposed in the nodes in which one link is connected to the others, strongly determines the accuracy of the calculated resonance frequencies of the robot

Trends in experimental modal analysis

Abstract The scope of this paper is to comment on current trends and new developments in the field of experimental modal analysis. The first section covers modal measurement and estimation procedures, with special emphasis on the use and limitations of recent techniques such as multiple input processing, total least square, global time- and frequency domain parameter estimation. In the second section reference is made to applications and use of modal parameters in techniques such as structural modification, fatigue and acoustic analysis. Emphasis is put on applications used at the Katholieke Universiteit, Leuven.