Nobuyuki Okubo

Improvement of Working Accuracy of a Machining Center by Computer Control Compensation

The study presents a method to improve working accuracy of a machining center by minicomputer. The geometrical error of the machine is estimated in advance by using a standard master part fixed on the table. Relative displacement between workpiece and spindle caused by thermal deformation of the machine is evaluated during operation using a simplified finite element model of the structure from temperature measurements taken of the machine tool. NC command pulses are modified by the computer so as to compensate for the geometrical error and deformation of the machine. Experimental results indicate that considerable improvement of working accuracy of the machining center is expected by means of this method.

Sensitivity analysis and its application for dynamic improvement

In order to determine appropriate points where natural frequency or mode shape under consideration can be effectively modified by structural modification, the theoretical background of sensitivity analysis is described, followed by experimental verification with a simple structure. Then it can be extended to (1) operational deflection shape, where a problem arises at offresonance frequency, (2) relative motion, (3) transmitted force through connecting points between components, (4) servo system, which consists of electrical elements with mechanical elements, and (5) acoustics generated by the vibration of the structure. To illusrate its effectiveness, many actual examples are given.

Vibration and Acoustic Analysis of Acoustic Guitar in Consideration of Transient Sound

The sound characteristic of an acoustic guitar is empirically designed for long time. The up to date vibration and acoustic analysis are applied to investigate the difference between typical guitars especially focused on transient vibration and sound just after picking a string at keynote and higher harmonic frequencies. By using a simplified front plate model of a guitar with bracings, structural modification method is utilized to realize the Operational Deflection Shape in order to meet the target sound characteristic.

Reduction of Radiating Sound from CFRP Laminated Plates with Orthotropy

CFRP is being positively introduced because of its light weight with sufficient stiffness for example in vehicle body but from acoustic aspect more investigations are needed. In order to grasp the vibration and acoustic feature of flat and curved CFRP laminated plates with orthotropy, the difference from isotropic material such as steel is clarified using experimental modal analysis. As a result CFRP is found to possess a dominant radiating sound mode shape at specific frequency. Then based on the FE model of the CFRP plate, a small CFRP patch with optimum anisotropy is designed to attach for effective reduction of the sound and finally its performance is verified in experiment.

Development of Vibration Damper for Energy Harvesting

In vibration engineering, unnecessary vibration energy can be dissipated by a damper into not only heat energy but also electric energy for energy harvesting. But a common damper for energy harvesting has to be tuned into a resonance in order to reserve large vibration and therefore for frequency varying case, the efficiency is very low and the application is limited. In this study a special damper system is so designed as to generate sufficient electric power even for frequency varying case based on two approaches: the resonance of the damper can be adjusted corresponding to the input frequency and the fixture of the damper has multiple resonances which coincide the structural resonances. The damper system consisted of permanent magnet and coil is verified to have variable resonance and the resonances of the damper fixture are found to have coincident resonances. Finally the damper system is applied to a motor bike where sufficient power is generated in case of varying engine rotation.

Vibration Reduction of Brush Cutter

Brush cutter powered by engine has been widely used on a daily basis for mowing of road shoulders and gardens. People who regularly operate brush cutter are at risk of developing Raynaoud’s disease due to large vibration. Such vibration disorder can be prevented by reducing the handle vibration by good use of structural modification. In this study we focused on rubber bushes which support the drive shaft in pipe to transmit the engine power to the cutting blade. First the dynamic characteristics of the brush cutter such as Operational Deflection Shape are grasped and then the hardness and the placement of rubber bushes are optimized to reduce the handle vibration effectively.

Biomechanical analysis for the epidural needle insertion

In order to test the hypothesis about reduction in the deformation of the ligamentum flavum due to tension inside the ligamentum flavum, nonlinear finite element (FE) analysis was employed. As a preliminary analysis of natural tissue, nonlinear FE analysis was applied to a rubber plate. Assuming that the rubber is third-order Mooney-Rivlin model, the analysis and the experimental curves overlap with each other until pierced point. The maximum major strain calculated by FE analysis was feasible to predict pierced point. To apply nonlinear FE analysis for the porcine ligamentum flavum, the Mooney-Rivlin coefficient of the porcine ligamentum flavum was identified from the tensile test data. Assuming that the sharp bar pierced the ligamentum flavum when the maximum major strain reached a constant value, the required displacement became shorter by 1.0mm by applying the initial tension.

Experimental Transfer Force Identification by Dynamic Stiffness Method and Reduction of Engine-Frame Coupled Vibration Based on Identified Force

In this paper, focusing on the coupled vibration of light weight vehicle engine and frame, the efficient method to reduce the vibration is discussed. First, target coupling vibration is explained by experimental data. And transfer force identification which transmits from the engine to the frame through the engine mount is carried out using dynamic stiffness method. In order to explain how the engine and the frame are coupling, the coupling index is introduced. The index is defined by inner products of the identified force and the frame FRF. Finally, the method to reduce the coupling index by adjusting the engine mount angle is proposed. The optimal adjustment angle is predicted and modifying the angle in experiment, it is shown that the adjustment method can reduce the coupling index and coupled vibration.

Experimental Realization of System-Level Vibration by Use of Single Component Based on Virtual Boundary Condition Concept

In order to meet the requirement of less vibration and less noise of complex machine, such as automobile, the system-level vibration test is carried out in spite of huge cost and time, which is conducted only when all components are able to be assembled. Although the vibration of individual component alone is different from the system-level, but a sophisticated component test is aimed to realize the system-level vibration at early development stage.

CAE Based Approach to Understand a Behavior of Vibro-Acoustic System

In this paper, a CAE based approach to understand a behavior of vibro-acoustic system is introduced. The sound pressure at an evaluation point in an enclosure can be described by inner product of (i)an acoustic transfer function from coupling surface to the evaluation point, and (ii)a structural vibration on the coupling surface. By addition of (iii)the correlation angle between above (i) and (ii), the sound pressure can be exactly estimated. In this paper, the correlation (iii) is called Vibro- Acousitc Coupling Factor (VAC). Using VAC, it is possible to understand not only the radiation efficiency, but also the interference of sound at the evaluation point. The proposing method explains the behavior of vibro-acoustic system using the frequency response of (i), (ii) and (iii). As an example, the proposing method is applied to FE model for improving the vibroacoustic characteristic.