Papers by Author: Hong Hee Yoo

Abstract: The operation error of a robot that occurs inevitably due to the manufacturing tolerance needs to be controlled within a certain range to achieve proper performance of the robot system. The reduction of manufacturing tolerance, however, increases the manufacturing cost in return. Therefore, design engineers try to solve the problem of maximizing the tolerance to reduce the manufacturing cost while minimizing the operation error to satisfy the performance requirement. In the present study, a revolute joint model considering uncertainties due to joint clearance is employed to perform a reliability analysis of the robot manipulator operation. The reliability analysis procedure employs single Monte-Carlo simulation and a statistical relation between the tolerance and the operation error. Significant reduction of computing time can be achieved with the proposed method. The present method is especially effective if sensitivity information is hard to be obtained for the analysis.

Abstract: In a mechanical system that has periodically repeated subcomponents, premature failures or malfunctions often occur. Due to slight irregularities of parameters of periodic systems, maximal frequency responses of a few subcomponents become often significantly larger than those of other subcomponents. These phenomena, called frequency response localization, need to be comprehended for reliable designs of the periodic systems. In the present study, the effects of parameter distribution patterns on the frequency response localization are investigated. Probabilistic results of the frequency response localization characteristics with two distinct parameter distribution patterns are exhibited.

Abstract: Dynamic stability of axially accelerated beams is investigated in this paper. The equations of motion of a fixed-free beam undergoing axially accelerated motion are derived. Unstable regions due to the acceleration are obtained by using the Floquet’s theory. Stability diagrams are presented to illustrate the influence of the acceleration characteristics. Large unstable regions of flutter type instability exist around the first, twice the first, and twice the second bending natural frequencies. Divergence type instability also occurs when the acceleration exceeds a certain value. The validity of the stability diagram is confirmed by direct numerical integration of the equations of motion.

Abstract: Flexible structures undertaking impact while undergoing overall motion can be found in several industrial products these days. Transient motion and stress induced by impact should be considered elaborately to extend the life of the products. In the present study, a modeling method for a flexible beam with a tip mass that undertakes impact while undergoes large overall motion is presented. The tip mass takes the impact force and the transient responses of the beam are calculated by employing the assumed mode method. The stiffness variation caused by the large overall motion is considered in this modeling. The effects of the tip mass and the angular speed of the beam on the transient responses are investigated.

Abstract: Nonlinear modeling method for the structural dynamic analysis of a micro cantilever beam actuated by electrostatic force is presented in this study. Static deflection is first obtained by solving nonlinear static equilibrium equation and the modal and the stability characteristics are calculated at the static equilibrium position. It is found that the amplitude and the frequency of the applied electrostatic voltage influence the stability of the structure significantly.

Abstract: For the design of a vibrating micro-beam structure, modal and stability analyses of the structure actuated by electrostatic force is performed in the present study. Static deflection of the micro-beam caused by the electrostatic force is first obtained by solving the nonlinear equilibrium equation and the modal and stability characteristics are calculated at the static equilibrium position. It is found that the amplitude and the frequency of the applied electrostatic voltage influence the stability of the structure significantly. A design specification of a vibrating micro-beam structure can be effectively determined from the modal and the stability analysis results.