Papers by Keyword: Vibration

Abstract: A high-speed, highly accurate positioning operation is required for industrial robots. However, residual vibration is generated in high-speed operation because industrial robots are cantilever structure. It takes the long settling time to the positioning operation. Acceleration feedback control is effective for vibration control. In the robot with two or more modes of vibration, the vibration mode besides targeted mode is excited by the difference of the vibration phase. In this paper, the phase relation and the vibration mode shape are clarified, and it aims at the control of the two or more modes using vibration node of the mode. The vibration modes are clarified by a modal analysis, and the vibration is controlled by the acceleration feedback. Using the vibration node of the mode stabilizes the difference of the phase of the first mode and the second mode. The effect of vibration control is verified by the experiment.

Abstract: Micro-aspheric lenses molded by micro-aspheric ceramic molds are increasing in the optical systems such as digital cameras and blu-ray players. To finish the molds with high accuracy and low surface roughness, in this paper, the micro-aspheric mold made of Electroless nickel plating are polished by using the newly developed 5-axis magnetostrictive vibration-assisted polishing machine. The magnetostrictive vibrating polisher generates a lateral vibration at 9.2 kHz with amplitude of 30 μm. The polishing pressure is controlled by a balance adjustment mechanism and the polishing load is controllable within a range of 2 mN ~ 20 mN with a resolution of 2 mN. The motion resolution of the X-Y-Z table is 0.1 μm in each direction. The C-axis rotary table is mounted on a B-axis tilting table and the workpiece is mounted on the C-axis rotary table with a vacuum chuck. According to the polishing experiments, the form accuracy was improved to 200 nm P-V and the surface roughness was reduced to 10 nm Rz (1 nm Ra).

Abstract: The characteristics of vibration and noise of an automobile have become important factors for evaluating automobiles. In this study, finite element modal analysis and harmonic analysis were used to analyze the dynamic characteristics of the bus bodywork. The analytical results show that vibration of ceiling board and floor board is large while the engine remains the idle running. The vibration of ceiling board and floor board are large during the engine running with the idle speed or the highest speed. In addition, the vibration of ceiling board and floor board also has peak values during the engine running with the maximum torsion moment. Therefore, for prediction of vehicle bodywork vibration and vehicle interior noise, the influence of the engine vibration on them should be considered in order to avoid resonance of bodywork boards and coupling of bodywork boards and interior acoustic field.

Abstract: Human ability to explore planets (e.g. the moon, Mars) depends on the autonomous mobile performance of planetary exploration robots, so studying on terrain classification is important for it. Vibration-based terrain classification unlike vision classification affected by lighting variations, easily cheated by covering of surface, it analyses the vibration signals from wheel-terrain interaction to classify. Three accelerometers in x, y, z direction and a microphone in z direction were mounted to arm of the left-front wheel. The robot drove on the sand, gravel, grass, clay and asphalt at six speeds, three groups of acceleration signal and one group of sound pressure signal were received. The original signals were dealt using Time Amplitude Domain Analysis. Original data were divided into segments, each segment was a three centimeters distance of driving; eleven features from every segment were normalized. The data from four sensors were merged into a forty-four dimensions feature vector. Ten one against one classifiers of Support Vector Machine (SVM) were used to classify; one against one SVM program from LibSVM was applied to multi-class classification using voting strategy in MATLAB. Facing to the same number of votes, we propose a new algorithm. Experimental results demonstrate the effectiveness of the feature extraction method and the multi-class SVM algorithm.

Abstract: Energy harvesting for powering low-power devices has drawn considerable attention over the last decade. This paper reports a novel tri-direction energy harvester to scavenge energy from wind and vibration, or a combination of them. The proposed harvester consists of a triple-level bimorph cantilever with a mass block to harness energy from ambient vibration. The mass block also acts as an aerofoil and bluff body to scavenge energy from wind. Theoretical analysis shows that the maximum output power of the harvester is 2.77 W, and the resonance frequency is 79 Hz.

Abstract: Harvesting energy from the environment has been widely investigated to power and maintain low-power devices. This paper reviews the potential energy sources, piezoelectric conversion mechanism, recently proposed piezoelectric energy harvesters (PEH), and micropower management circuits. It can be concluded that the output power of PEH is still comparatively small, especially when the ambient excitation frequencies deviate from PEH’s resonant frequency. Future work should focus on tuning or widening the operate frequency of PEH so that it can match the ambient vibration frequency at all time. Moreover, flow energy harvesting techniques compatible with MEMS techniques demand in-depth study to facilitate the fabrication of micro PEHs.

Abstract: A new type of instrument is designed to accomplish the purpose of localizing the sound source by a relatively compact structure. This bionics structure is designed to mimic the localization function of the ears of the parasitoid fly Ormia ochracea, and it consists of three elastic diaphragms, three bars which connected to the diaphragms, and the other mechanical components. The analysis of this structure’s dynamic behavior shows that the incident angles of the sound have special relationship to the responses of this instrument, and the incident angles can be estimated by detecting the vibrations of the three elastic diaphragms.

Abstract: Optical freeform surfaces have a strict request on surface quality, but the vibration of tool , which is often ignored in previous studies, have a great influence on surface topography in micro-milling. This paper constructs a micro-milling motion model concerned with tool vibration, and the impact of tool vibration on feed-interval scallop in micro-milling is analyzed. The results show that tool vibration always lead to an increment of surface roughness; and vibration amplitude and feed per tooth are the major factors that have an effect on feed-interval scallop form and surface quality.

Abstract: This paper presents the vibration and surface roughness issue of poly methyl methacrylate (PMMA) workpiece produced by micro end milling using integrated multi-process machine tools DT 110 (Mikrotools Inc., Singapore) with control parameter; spindle speed, feed rate, and depth of cut. The vibration was measured using accelerometer, DYTRAN Instrument and the average surface roughness Ra was measured using Wyko NT1100. The optimum solution for minimum average vibration is 64.3 Hz with spindle speed 3000 rpm, feed rate 2 mm/min, and depth of cut 1.5 μm. However, the optimum solution for minimum average surface roughness, Ra is 0.352 μm with spindle speed 2000 rpm, feed rate 2 mm/min, and depth of cut 1.5 μm. The micro end milling parameters are suitable to machine PMMA to get good precision surface roughness. The analysis revealed that the feed rate and depth of cut is the most influential parameter on vibration during machining process meanwhile for average surface roughness, Ra spindle speed is the most influential parameter.

Abstract: Comparative analyses of dynamic characteristics between two aluminum alloy single-layer spherical shells, which have the same span, same rise-span ratios and same bars but different material characters of elasticity and visco-elasticity, are presented. Influences about material viscosity on vibration behaviors of single-layer spherical aluminum alloy reticulated shells are illustrated. The results show that: there are great differences between the resonance frequencies of two shells but the linear harmonic response properties are basically the same; the dynamic characteristics of these two shells are greatly different under harmonic loads or seismic loads, and the dynamics characteristics are greatly influenced by the viscous properties of the material itself.