Papers by Keyword: Resonance Vibrations

Abstract: Modal analysis of machine center was carried out by means of finite-element analysis (FEA) method to get its characteristics and to improve its machining precision. Based on this, harmonic response analysis was processed to evaluate its vibration when the cycle load caused by the machining force was applied on the main shaft of machine center, which was used to provide clues for avoiding resonance vibration and ameliorating design.

Abstract: Flying robots with flapping wings are preferred over conventionally fixed or rotational wings in terms of hovering capability for a simple mechanical configuration. Until recently, available actuators for such a robot are limited to (1) a conventional motor with four-bar linkage mechanism or (2) a piezo electric actuator, but none of them could provide enough lift because of low flapping frequency, small stroke angles, and/or frequent mechanical failure. A new actuator capable of generating large stroke angles with high frequency is developed. It consists of an out-runner brushless motor with a modified motor driver attached to a torsion spring. The wing is attached directly on the cap of the motor. A prototype is built and preliminary thrust force measurements are performed. Properties of wing materials suitable for powerful and robust actuators will be discussed. The actuator employed in the present study utilizes resonance oscillation, which leads to high energy efficiency. Further study of wing shape and directional stiffness is needed for generating higher lift capability.

Abstract: An experimental approach for fast crack detection and length determination in fullsize solar-grade crystalline silicon wafers using a Resonance Ultrasonic Vibrations (RUV) technique is presented. The RUV method is based on excitation of the longitudinal ultrasonic vibrations in full-size wafers. Using an external piezoelectric transducer combined with a high sensitivity ultrasonic probe and computer controlled data acquisition system, real-time frequency response analysis can be accomplished. On a set of identical crystalline Si wafers with artificially introduced periphery cracks, it was demonstrated that the crack results in a frequency shift in a selected RUV peak to a lower frequency and increases the resonance peak band width. Both characteristics were found to increase with the length of the crack. The frequency shift and bandwidth serve as reliable indicators of the crack appearance in silicon wafers and are suitable for mechanical quality control and fast wafer inspection.