Case Studies in Mechanical Systems and Signal Processing最新文献

During high level vibration test on a high mass specimen, the test engineer is often facing difficulty to pass properly the specified vibration level due to coupling between the specimen and the shaker. The present paper present a methodology to define a virtual shaker testing simulator. The first step involves the dynamic identification of a 80 kN shaker performed thanks to measurements (modal analysis and sine sweep). The second step is the definition of the physic represented in the simulator and the translation of the electromechanical equations in a home-made simulator. Controller developed by SIEMENS LMS and supplied to V2i for a use in the framework of the AOC project is introduced to close the loop. Two test cases are described to demonstrate the possibilities offered by the simulator.

Rotor imbalance is the most common cause of machine vibration. In practice, rotors can never be balanced perfectly owing to manufacturing errors such as porosity in casting, non-uniform density of materials, manufacturing tolerances, and gain or loss of material during operation. Mass imbalance leads to the generation of a centrifugal force, which must be counteracted by bearings and support structures. A full spectrum analysis is presented for vibration signal to reveal the fault specific whirl signatures. The results clearly indicate the potential and feasibility of the discussed approach for the rotor imbalance diagnosis in a rotor shaft system coupled with a three phase induction motor. This paper presents a smart experimental method for vibration measurement and imbalance fault detection in rotating machinery.

This paper presents a proposal for a minimum energy feedforward control technique for flexible structures to suppress residual vibrations in point-to-point (PTP) motion. In the proposed method, the trajectory profile of the PTP motion is generated through a cycloidal function whose input is the output of a polynomial function. The obtained trajectory is dependent upon the coefficients of the polynomial function. To achieve the suppression of the residual vibration as well as the operating energy of this PTP motion, the coefficients are tuned by metaheuristic algorithms. In the numerical simulations, we investigated the PTP motions of a single-link flexible manipulator and a robotic arm attached to a flexible link. The simulation results were compared with those of previous studies, revealing the effectiveness of the proposed method.

Impact dampers were first introduced in 1934 and the research and development on improving their performance and configuration is still ongoing to date. In this paper, the recently developed Linear Particle Chain (LPC) impact damper is experimentally and numerically studied. The damper was attached to a single-degree-of-freedom structure represented by a spring damper system and released from an initial position. A SOLIDWORKS model for the damper has been developed and numerically simulated using the finite element approach. The Coulomb friction model of the colliding masses is added to the overall structure. The response of the system was analyzed and compared to the experimental results. The simulation model showed a faster decay when the number of balls in the LPC impact damper was increased and when different mass ratios were used which is in agreement with the experimental results.

This work presents experimental results of two damage detection techniques based on modal properties, with the application on a full-size composite helicopter main rotor blade. The damage detection methods used in this study are the coordinate modal assurance criterion (COMAC) and the modal strain energy method, which are respectively based on the comparison of vibration modes and on the comparison of the modal strain energy of a beam. Modal parameters were obtained with experimental modal analysis and damage was introduced artificially on the blade by attaching a small mass to it, changing its global properties in this way. Finally, experimental results for the damage detection technique are shown for both methodologies, and remarks concerning sensitivity and robustness of the methods are discussed.

The simulation tools are the foundation for the design of robot systems, for the application of robots in complex environments and for the development of new control strategies and algorithms. Because of this, the design, simulation and comparison of the performance of controllers applied to a redundant robot with five degrees of freedom (DOF) are presented in this paper. Through homogeneous transformation matrices the inverse kinematic model of the redundant robot is obtained. Six controllers are prepared to test the robot’s dynamic model: hyperbolic sine–cosine; computed torque; sliding hyperbolic mode; control with learning; and adaptive. A simulation environment is developed by means of the MatLab/Simulink software, which allows analyzing the dynamic performance of the robot and of the designed controllers. This simulation environment is used to carry out different tests of the redundant manipulator model together with each controller as they are made to follow a trajectory in space. The results, obtained through a simulation environment, are represented by comparative curves and RMS indices of the joint and Cartesian errors, and they show that the redundant manipulator model follows the test trajectory with less pronounced maximum errors using the adaptive controller than the other controllers, with more homogeneous motions of the manipulator. The largest joint and Cartesian errors generated when testing the robot model, both in terms of maximum and RMS values, occurred when the computed torque controller is used. The results with that controller are obtained by executing three iterations for learning, because with more iterations the variations were not important.