One of the key factors in designing a motor built-in high speed spindle is to assemble the motor rotor and shaft by means of hot-fit. Presented in this paper is a study of the influence of a hot-fit rotor on the local stiffness of the hollow shaft. Dynamic analyses of the rotor-hollow shaft assembly using contact elements are conducted. The normal contact stress state between the rotor and the hollow shaft is obtained through the use of contact elements with friction effects included. The normal contact stress, considered as the pr-stress between the rotor and the hollow shaft, is then adopted for subsequent modal analyses. In this study, the modal analysis results are verified by a modal testing experiment. The percent errors of the first natural frequency and the second natural frequency are down to about 0.58% and 0.79%, respectively.

Developing a motor-built-in high speed spindle is an important key technology for domestic precision manufacturing industry. The dynamic analysis of the rotating shaft is the major issue in the analysis for a motor-built-in high speed spindle. One of the major concerns is how the motor rotor is mounted on the shaft, by interference (shrink) fit or else. In this study, dynamical analyses are carried out on a motor-built-in high speed spindle. The motor rotor is mounted on the spindle shaft by means of interference fit. Modal testing and numerical finite element analyses are conducted to evaluate the dynamical characteristics of the spindle. The stiffness of the shaft accounting for the interference fit is investigated for the finite element model of the spindle. This study also proposes an analysis procedure to dynamically characterize the high speed spindle with a built-in motor. Based on the results of modal testing and the numerical analyses, it may conclude that the proposed procedure is feasible for the spindle and is effective for other similar applications.

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In our previous work, a frequency-domain method for estimating the mass, stiffness and damping matrices of a structure was presented. In that method, the accuracy of identified system matrices for different data point configurations are addressed and shown that a more accurate damping matrix can be identified and the present method is insensitive to the data point configurations used in the identification procedure even for cases with only few data points. In this paper, a system matrices reduction method for a damped system is proposed. In this reduction method, a mapping matrix is formulated based on the original complex mode shapes and utilized to transform the original system matrices to reduced ones, which possess the selected modes of original system. The selection of active degrees of freedom is also addressed in this paper. The simulated and experimental results indicate that the reduction method is effective and accurate.

In general engineering practice, one key factor in designing a motor built-in high-speed spindle is to assemble the motor rotor and shaft by means of hot-fit to form a new rotor-shaft assembly. In this paper, the dynamic analysis of a hot-fit rotor in a rotor-shaft assembly by using 3D contact element is proposed. Contact pressure between the rotor and the shaft is firstly calculated through contact theory. The stress state is thus determined. The finite element modal analysis then follows with the stress state as a pre-stressed condition. The accuracy and the validity of the finite contact element results are verified by theoretical formulation, equivalent static analysis and experimental modal testing. The results presented herein indicate that it is accurate and effective in analyzing the dynamic behavior of the rotary shaft system with a hot-fit component by using contact element.

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Portable electronic products such as portable instruments are susceptible of drop impacts. Therefore the effects of impact and shock on the integrity of the instrument body as a whole and the internal components including the printed circuit board (PCB) are important reliability issues and hence need to be addressed. The impact orientation is one of the major factors that influence the dynamic responses of the instrument structure. This paper presents a study, using ANSYS/LS-DYNA, of drop/Impact responses of the body structure of commercially available potable measurement instruments. The instrument is set to free fall drop with three impact angles 0 , 45 , and 90. The responses including the variations of stress and strain are evaluated on the housing cases and internal PCBs of the instrument. The results show that the subsequent impacts that follow the first impact also contribute noticeable influences to the structure of the instrument. The results of this study can be the bases for the design of drop concerns of general portable measurement instrument.

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