Hong Jae Yim

A study on joint compliance for a biped robot

Dynamic simulations are often used to design mechanisms and to develop control algorithms for stable walking of the humanoid robot. For accurate dynamic simulations, the flexible compliances at the joints of the humanoid robot must be considered in the computer simulation model. In this paper a method to identify the proper compliances among the joints is presented. Dynamic simulations with the proposed method are compared with the test results

A Study on the Fatigue Life Prediction of OHT Vehicle Structures Using the Modal Stress Recovery Method

In this paper, a computer aided analysis method is proposed for a durability assessment in the early design stages using the Modal Stress Recovery (MSR) and the linear damage rule. From a dynamic analysis of the OHT vehicle system with some flexible bodies, modal displacement time histories of vehicle structure components are calculated. From finite element analysis of components, modal stresses are calculated. With the modal displacement time history and the modal stress of the component, the dynamic stress time history at the critical location is produced using the superposition principle. Using the linear damage rule and the cycle counting method, the fatigue life is predicted from the dynamic stress time history. The process of predicting the fatigue life using the proposed computer models in this paper may be applied to structures of various dynamic systems.Copyright

The Design of a Patient Transportation Robot's Lifting Arms Considering Comfort and Safety without the Presence of a Sheet

A transportation robots lifting arms have an effect on the comfort and safety of patients. Improved arms have been designed through dynamic and static analyses to increase safety if a sheet not present on the lifting arms. To design the lifting arms, experimentation is very helpful, however, it is difficult and dangerous to experiment on patients; therefore, a simple human model was made and used for the dynamic analysis. Through the dynamic analysis results, a safe width and comfortable location for the lifting arms were determined. The thickness was then determined by static analysis and optimum design. In addition, tests have been conducted to confirm comfort and safety by deploying the designed lifting arms onto a transportation robot.

Fracture Behavior of Glass/Resin/Glass Sandwich Structures with Different Resin Thicknesses

Glass/resin/glass laminate structures are used in the automobile, biological, and display industries. The sandwich structures are used in the micro/nanoimprint process to fabricate a variety of functional components and devices in fields such as display, optics, MEMS, and bioindustry. In the process, micrometer- or nanometer-scale patterns are transferred onto the substrate using UV curing resins. The demodling process has an important impact on productivity. In this study, we investigated the fracture behavior of glass/resin/glass laminates fabricated via UV curing. We performed measurements of the adhesion force and the interfacial energy between the mold and resin materials using the four-point flexural test. The bending-test measurements and the load-displacement curves of the laminates indicate that the fracture behavior is influenced by the interfacial energy between the mold and resin and the resin thickness.

Walking Pattern Generation employing DAE Integration Method

A stable walking pattern generation method for a biped robot is presented in this paper In general, the ZMP (zero moment point) equations, which are expressed as differential equations, are solved to obtain a stable walking pattern However, the number of differential equations is less than that of unknown coordinates in the ZMP equations It is impossible to integrate the ZMP equations directly since one or more constraint equations are involved in the ZMP equations To overcome this difficulty, DAE (differential and algebraic equation) solution method is employed The proposed method has enough flexibility for various kinematic structures Walking simulation for a virtual biped robot is performed to demonstrate the effectiveness and validity of the proposed method The method can be applied to the biped robot for stable walking pattern generation

Analysis on Improvement for Garage Shift Quality of Independent Rear Suspension of Front Engine Rear Wheel Drive Vehicle

In this study, multi-body dynamic analysis was conducted to improve the shift feel that occurs while parking a car. A multi-body, dynamic simulation model of a vehicle was developed by using an independent rear suspension(IRS) and a rigid-axle suspension. To evaluate the shift feel, the displacement target of the upper-arm bushing was set with the help of a rigid-axle simulation model when the gear was disengaged. In the simulation, a shift shock with a displacement value that was above the limit was confirmed. Sensitive parts resulting in shift feel were derived from the simulation. To improve the shift feel of the IRS vehicle, the cause for such shift feel was investigated, and countermeasures were proposed. By applying the result of this analysis to a car, it would be possible to improve the shift feel. Therefore, the incompatibility between IRS and rigid-axle vehicles was resolved.

A Study on Crashworthiness Optimization of Front Side Members using Bead Shape Optimization

In this study, the front side member is optimized using a topography optimization technique. Optimization of a simple beam is conducted before optimization of the front side member. The objective function is set to minimize the first buckling factor in the longitudinal direction. The design variable corresponds to the perturbation of nodes normal to the shells mid-plane space. The crash analysis is conducted on a simple beam, which is optimized by Response Surface Method and the topography optimization technique. In order to verify the topography optimization technique, the results of the RSM and topography optimization model are compared. Consequently, we confirm the satisfactory performance of the topography optimization technique, and apply this topography optimization to the front side member. Thus, the front side member is optimized and its crashworthiness is increased.

Walking Pattern Generation for a Biped Robot Using Polynomial Approximation

In this paper, a stable walking pattern generation method for a biped robot is presented. A biped robot is considered as constrained multibody system by several kinematic joints. The proposed method is based on the optimized trunk motion along the moving direction. Foot motions can be designed according to the ground condition and walking speed. To minimize the deviation from the desired ZMP, the trunk motion is generated by the fifth order polynomial approximation. Walking simulation for the virtual biped robot is performed to demonstrate the effectiveness and validity of the proposed method. The method can be applied to the biped robot for stable walking pattern generation.Copyright

A Study on Numerical Solution Method for Efficient Dynamic Analysis of Constrained Multibody Systems

An efficient computational method for the constrained multibody systems is proposed. In the proposed method, local parametrization method is employed to apply the same solution method for position, velocity, and acceleration analyses since the coefficient matrices for each analysis have an identical matrix pattern. The skyline solution method is used to overcome numerical inefficiency when solving large scaled equations. Subsystem partitioning method is derived systematically to perform parallel processing for the real time simulation. To show the numerical accuracy and efficiency of the proposed method, three numerical problems are solved.Copyright