Control of Rotary Cranes Using Fuzzy Logic

Rotary cranes (tower cranes) are common industrial structures that are used in building construction, factories, and harbors. These cranes are usually operated manually. With the size of these cranes becoming larger and the motion expected to be faster, the process of controlling them became difficult without using automatic control methods. In general, the movement of cranes has no prescribed path. Cranes have to be run under different operating conditions, which makes closed-loop control preferable. In this work a fuzzy logic controller is introduced with the idea of split-horizon; that is, fuzzy inference engines (FIE) are used for tracking the position and others are used for damping the load oscillations. The controller consists of two independent controllers: radial and rotational. Each of these controllers has two fuzzy inference engines (FTEs). Computer simulations are used to verify the performance of the controller. Three simulation cases are introduced: radial, compound, and damping. The results from the simulations show that the fuzzy controller is capable of keeping the load-oscillation angles small throughout the maneuvers while completing them in a relatively reasonable time.

Wavelet Based Demodulation of Vibration Signals Generated by Defects in Rolling Element Bearings

Envelope detection or demodulation methods for bearing vibration response signals have been established as a dominant analysis method for bearing fault diagnosis, since they can separate the useful part of the signal from its redundant contents. A new effective demodulation method is proposed, based on the Discrete Wavelet Transform (DWT). The method fully exploits the underlying physical concepts of the modulation mechanism, present in the vibration response of faulty bearings, using the excellent time-frequency localization properties of the wavelet analysis. Two key elements, resulting to the successful implementation of the method, are its practical independence from the choice of the specific wavelet family to be used and the limited number of the wavelet levels, that are required for its practical application. Experimental results and industrial measurements for three different types of bearing faults, confirm the validity of the overall approach.

Using Triaxial Accelerometer Data for Vibration Monitoring of Helicopter Gearboxes

Typical vibration monitoring systems for helicopter gearboxes rely on single-axis accelerometer data. This paper investigates whether triaxial accelerometers can provide crucial flight regime information for helicopter gearbox monitoring systems. The frequency content of the three different directions is compared and analyzed using time-synchronously averaged vibration data. The triaxial data are decorrelated using a mathematical transformation, and compared to the original axes to determine their optimality. The benefits of using triaxial data for vibration monitoring and diagnostics are explored by analyzing the changes in the direction of the principal axis of vibration formed using all three axes of vibration. The statistical variation introduced due to the experimental variables is further analyzed using an Analysis of Variance approach to determine the effect of each variable on the overall signature. The results indicate that triaxial accelerometers can provide additional information about the frequency content of helicopter gearbox vibrations, providing researchers and industry with a novel method of capturing and monitoring changes in the baseline vibration signatures.

Design of a Scaled Model for a High Rise, High Speed Elevator

A novel scaled model is developed to simulate the linear lateral dynamics of a hoist cable with variable length in a high rise, high speed elevator. The dimensionless groups used to formulate the scaling laws are derived through dimensional analysis. The model parameters are selected based on the scaling laws subject to space and hardware constraints. It is demonstrated that while it is almost impossible to obtain a fully scaled model unless the model is extremely tall, a reasonably sized model can be constructed with sufficient accuracy. The scaling laws that are not satisfied can be rendered to have a minimal effect on the scaling between the model and prototype. In conjunction with the model design, an analysis of model tension in a closed cable loop is developed. A new movement profile, which ensures a continuous jerk function during the entire period of motion, is derived. Practical considerations that occur in the design of the model are addressed. The methodology can be used to investigate the vibration of a very long cable in other applications.

Prospect of Applying Controlling Chaotic Vibration in the Waterborne-Noise Confrontation

This paper taking the Duffing system with nonlinear soft stiffness as an example, discusses the possibility of applying the chaotic phenomenon to get a broadband frequency output for a single frequency input. Thereby proves the application value of controlling chaos in the waterborne-noise confrontation.

Control of a Buckled Beam Subjected to a Compressive Force

In this paper, we deal with a stabilization control for the buckled beam subjected to a compressive force. It is easily predicted that by applying a restoring force to the beam (P control), which is proportional to the deflection, the critical compressive force for the buckling is increased. However it is theoretically and experimentally clarified in our former study that in the neighborhood of the critical point, the effect of Coulomb friction at the supporting points is relatively increased even if it is very slight. It follows that the beam cannot be stabilized to the trivial steady state only by using the position feedback control and also velocity feedback. In this paper, we propose a stabilization control method of the beam to the trivial steady state by the aid of disturbance observer. Furthermore, the validity of the theoretically proposed method is experimentally confirmed.

Axial Nonlinear Mechanical Vibrations of Large Power Transformer Windings During Short Circuit

In this paper, the axial nonlinear vibrations of the transformer winding under steady state operation case and short circuit case are studied in single degree and multi-degree models. In the case of having ampere-turn balance, the steady state response of the former model is obtained by using multi-scale method and periodic shooting method, analytically and numerically. At the same time, the computing method of Jacobi matrix in the periodic shooting method has been modified, so that the computing CPU time is saved. For multi-degree mechanical model of a single phase transformer windings, the time domain response and relation between the response and various parameters are obtained by Runge-Kutta method. For ampere-turn unbalance case, an electric-mechanical coupled problem, that the electric force depends the displacement of the winding are foomed, and the nonlinear forced Mathieu equation is established for this problem; and then the nonlinear dynamical response and global dynamical behaviors are analyzed. Finally, for a 20 MVA single phase three windings transformer, a series of short circuit experiments have been performed and the axial dynamical response force, magnetic field, strain etc. have been measured. The theoretical results well agree with the experimental results.

Chaotic Motion in the Vicinity of Separatrix of a Parametrically Driven Duffing Oscillator With a Twin-Well Potential

The conditions for the (M:1) and (2M:1) resonances inside and outside of the separatrix of the parametrically driven Duffing oscillator are determined. The onset of such resonance in the vicinity of separatrix is investigated analytically and numerically. The results presented in this article can be applied to the post-buckled structures under parametric excitations.

Bifurcations and Chaos in Forced, Coupled Pendula

We consider forced, coupled pendula and show that they exhibit very complicated dynamics using the averaging method and Melnikov-type techniques. First, the averaged system for small oscillations of the pendula near the hanging state is analyzed. Codimension-one and -two local bifurcations at which several non-synchronized periodic orbits and quasiperiodic orbits are born in the original system are detected. The validity of the theoretical results is demonstrated by comparison with direct numerical integration results. Moreover, chaotic motions, which result from the Shilnikov type phenomena in the averaged systems, are observed in numerical simulations. Second, the second-order averaging method is applied to small perturbations of rotary orbits with no damping and external forcing. Analyzing the averaged system, we can describe nonlinear behavior in the original system. Finally, using a generalization of Melnikov method, we prove the occurrence of many other homo-clinic phenomena, which also yield chaotic dynamics.

Dynamics of Oscillator With Soft Impacts

The impact oscillator is the simplest mechanical system with one degree of freedom, the periodically excited mass of which can impact on the stop. The aim of this paper is to explain the dynamics of the system, when the stiffness of the stop changes from zero to infinity. It corresponds to the transition from the linear system into strongly nonlinear system with rigid impacts. The Kelvin-Voigt and piecewise linear model of soft impact was chosen for the study. New phenomena in the dynamics of motion with soft impacts in comparison with known dynamics of motion with rigid impacts are introduced in this paper.