Roland Horvath

Modeling early stage fretting of electrical connectors subjected to random vibration

Fretting corrosion induced by vibration is a topic of major concern for automotive applications, often leading to increased contact resistance and connector failure. Presently, modeling of the behavior of connectors during fretting corrosion is a difficult matter, requiring many parameters, and is generally highly nonlinear in nature. Experimental testing of sample connectors is currently the only practical method of evaluating connector performance; however, testing can be a time-consuming and inexact task. Prior work by the authors studied the fretting behavior of connectors subjected to single frequency vibration. Correlation of experimental results with simulated behavior showed that, for the primary mode of connector interface motion observed (rocking-type motion), the relative moment at the interface was a good indicator of the observed fretting rate. It was also shown that the moment applied as the result of a given excitation level and frequency could reasonably be predicted via simulation. The current work extends this approach to random vibration profiles, which are a more realistic representation of the connector application environment. A simple model is developed which relates the early stage fretting corrosion rate to the threshold vibration levels for the connector, the dynamic characteristics of the connector/wiring configuration, and the vibration profile. A high degree of consistency between this model and the experimental data was demonstrated. Interestingly, regardless of the excitation profile applied to the overall system, the existence of a characteristic vibration threshold at the connector interface was observed.

The influence of contact interface characteristics on vibration-induced fretting degradation

Vibration induced fretting degradation is a widely recognized failure phenomenon; however, the basic mechanisms that control the onset and progression of such fretting behavior are not well understood and are a topic of considerable interest in the electrical connector community. One specific issue is the need for a more detailed understanding of the mechanisms controlling the fretting degradation. The present study addresses these questions and develops answers using the results from a series of experimental tests of sample connectors which are subjected to single-frequency vibration profiles at room temperature. These test specimens are a series of dual-row 16-circuit automotive connectors in which the plating finish and contact normal force are varied. The results are presented and discussed in light of earlier investigations.

Micromachined Vibration Isolation Filters to Enhance Packaging for Mechanically Harsh Environments

Some harsh environments, such as those encountered by missiles, rockets and various types of industrial machinery, contain high frequency mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency vibrations. Examples include MEMS gyroscopes, oscillators and some micro-optics. Exposure to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. Since they usually possess a low vertical profile, they can be utilized as the packaging substrate for the sensitive component requiring vibration isolation. The performance of these filter structures is typically limited by low damping and a lack of tunability after fabrication. However, filter performance can be enhanced by integrating fluidic damping techniques with the passive filter or by integrating a ...

Passive Balancing of Rotor Systems Using Pendulum Balancers

Passive balancing techniques have received a great deal of attention in recent literature, with much of this work focused on ball balancer systems. However, for certain applications, balancing systems that use pendulums rather than rolling balls may offer distinctly improved balancing precision. This investigation seeks to provide additional insight into the performance and expected behavior of such systems. A simulation model is developed for a pendulum balancer system with isotropic supports and analyzed in detail. The influence of shaft location and friction on balancing effectiveness is considered and evaluated. In this regard, the dynamic characteristics of a pendulum balancer system are analyzed and compared to a similar ball balancer system. The conclusions and observations from the analysis and simulation studies are demonstrated and tested in a series of experimental studies.

Passive Balancing for Rotor Systems Using Pendulum Balancers

An analytical, numerical and experimental investigation of the dynamic behavior of a passive balancing system is presented. Due to the system constraints and dynamic characteristics, this system is capable of combined static and dynamic mass balancing. This work is an extension of previous studies in which ball-balancing systems were used to reduce harmful vibration caused by radial perturbation in the principal axis of inertia. In the present research, the imbalance compensation problem is divided into axial and radial components. A spherical suspension was applied at the rotational axis that allows the rotating disk to tilt, thus eliminating coupled dynamic centrifugal forces caused by the axial mass imbalance. In a fashion similar to earlier ball balancing systems, in this study the balancing balls were replaced by two single pendulums suspended in the geometrical axis of a disk in order to compensate for radial unbalance. The governing equations are developed, which results in a set of cross-coupled nonlinear differential equations, which are analyzed in detail. An experimental study is also conducted to validate and test the conclusions of the analysis and simulation work.Copyright

Damping control of micromachined lowpass mechanical vibration isolation filters using electrostatic actuation with electronic signal processing

Some harsh environments, such as those encountered by aerospace vehicles and various types of industrial machinery, contain high frequency/amplitude mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency mechanical vibrations. Examples include MEMS gyroscopes and resonators, oscillators and some micro optics. Exposure of these components to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. However, the performance of these filter structures is typically limited by low damping (especially if operated in near-vacuum environments) and a lack of tunability after fabrication. Active filter topologies, such as piezoelectric, electrostrictive-polymer-film and SMA have also been investigated in recent years. Electrostatic actuators, however, are utilized in many micromachined silicon devices to generate mechanical motion. They offer a number of advantages, including low power, fast response time, compatibility with silicon micromachining, capacitive position measurement and relative simplicity of fabrication. This paper presents an approach for realizing active micromachined mechanical lowpass vibration isolation filters by integrating an electrostatic actuator with the micromachined passive filter structure to realize an active mechanical lowpass filter. Although the electrostatic actuator can be used to adjust the filter resonant frequency, the primary application is for increasing the damping to an acceptable level. The physical size of these active filters is suitable for use in or as packaging for sensitive electronic and MEMS devices, such as MEMS vibratory gyroscope chips.

Influence of Nonideaities on the Performance of a Self-Balancing Rotor System

An analytical, numerical and experimental investigation of the dynamic behavior of a four degree of freedom passive balancing system using pendulum balancers is presented. This work is an extension of previous studies which considered such automatic balancing systems and devices. It has previously been demonstrated analytically that a 4-DOF pendulum self-balancing system is capable, under idealized conditions, of exact radial balancing [10]. However, imperfections in the fabrication and assembly of such a system tend to compromise a number of the ideal modeling assumptions that were used to provide this result. The present research study examines the effects of a variety of such imperfections and their influence on the functional capability of the self-balancing system. Both analytical/simulation results and experimental validation are provided and discussed.© 2005 ASME

Experimental validation and testing of components for active damping control for micromachined mechanical vibration isolation filters using electrostatic actuation

Missiles, rockets and certain types of industrial machinery are exposed extreme vibration environments, with high frequency/amplitude mechanical vibrations which may be detrimental to components that are sensitive to these high frequency mechanical vibrations, such as MEMS gyroscopes and resonators, oscillators and some micro optics. Exposure to high frequency mechanical vibrations can lead to a variety of problems, from reduced sensitivity and an increased noise floor to the outright mechanical failure of the device. One approach to mitigate such effects is to package the sensitive device on a micromachined vibration isolator tuned to the frequency range of concern. In this regard, passive micromachined silicon lowpass filter structures (spring-mass-damper) have been developed and demonstrated. However, low damping (especially if operated in near-vacuum environments) and a lack of tunability after fabrication has limited the effectiveness and general applicability of such systems. Through the integration of a electrostatic actuator, a relative velocity sensor and the passive filter structure, an active micromachined mechanical lowpass vibration isolation filter can be realized where the damping and resonant frequency can be tuned. This paper presents the development and validation of a key component of the micromachined active filter, a sensor for measuring the relative velocity between micromachined structures.

Vibration Analysis and Health Monitoring of Cracks in Composite Disk Rotor Systems

Cracks and voids are common defects in rotating systems and are a precursor to fatigue-induced failure. Identifying the presence and growth of cracks is a critical concept for the health monitoring and diagnostics of such systems. A combined computational and experimental study of the vibration characteristics of a composite hub flywheel rotor system with a cracked hub disk is presented. First, experimental testing of both in-plane and out-of-plane vibration characteristics using a rotor with a composite disk hub supporting a relatively massive rim was conducted. A crack was deliberately introduced into the hub disk during fabrication. Based upon these results, a finite element (FEA) model was developed to further explore the relationship between natural frequencies and crack properties. Finally, a simplified theoretical model for the primary in-plane vibration mode was developed and used in a series of parametric studies. Good agreement was found between the model predictions and the experimental results. It was observed that the presence of a crack tends to affect both the magnitudes and distribution of the rotor natural frequencies. Certain primary frequencies for rotors with a crack are smaller than for those without a crack. In addition, the frequency values of associated with the “in-crack” direction are generally smaller than those associated with the “off-crack” direction, introducing a non-symmetry into the rotordynamics which can serve as an indicator for rotor health monitoring.Copyright

Stability Investigation of a Two-Link 3DOF Rotational Pendulum

A numerical and experimental investigation of the dynamic behavior of a two-link, 3 degree of freedom (DOF) rotational pendulum is presented. This work extends previous studies of two-link 2DOF rotational pendulum systems in which the links were connected to each other and to the main driver by 1 DOF pinned joints. In the present study, an additional degree of freedom is added in which the first link is connected to the main driver shaft by a 2DOF cardanic joint. The two links are still connected by a pinned joint. It is observed that such systems have inherent zones of instability. A stable zone and an unstable zone, separated by a specific critical angular velocity, were identified. If the rotational speed is under this critical value, the mechanical system shows asymptotic stability. For rotational speeds above this value, the system shows instability around a static bifurcation.Copyright