Seungchul Lim

Motion control of biped robots using a single-chip drive

In order to be a performance-enhanced, standalone system legged robots are desired to have an effective mechanism and lightweight control hardware. In the context, this paper shows how to design a biped robot adopting a field programmable gate array, or FPGA for short, as the motor controller. Additionally, the onboard electronic hardware system features a digital signal processor (DSP) as the main CPU. By using the FPGA in conjunction with PWM RC servomotors, a more flexible hardware system has been accomplished with the integrated, digital controller.

Locomotion of Dog-like Quadruped Robots: Walk and Trot

ABSTRACTThis paper is concerned with locomotion of dog-like quadruped robots that can adapt to various terrains, mainly dealing with implementation methods and characteristics of static and dynamic gaits. To this end, a 12-DOF robot is built in house, motional trajectories of its body and feet are generated mimicking biological life, and the corresponding leg joint angles are analytically obtained by inverse kinematics. Such joint angle data are then applied to the robot’s ADAMS model for computer simulations so that the planned walk and trot gaits are both confirmed dynamically stable. However, contrary to the simulation results, previous trot patterns showed unstable behavior during experiments. This problem led us to analyze the reason, and in the course we discovered the importance of maximally utilizing the concept of WSM rather than ZMP and therefore reducing the gait period to secure the stability of dynamic gaits such as trot. Key words : Kinematics, Dynamic Stability, ZMP(Zero Moment Point), WSM(Wide Stability Margin)요 약본 논문은 다양한 지면에 적응 가능한 견형 4족 로봇의 위치 이동에 관한 것으로 정 보행과 동 보행의 구현 방법 및 특성을 주로 다루었다. 이를 위하여, 총 12 자유도의 로봇을 자체 제작하였으며 , 몸통과 발의 운동궤적을 생체 모방 방식으로 생성한 후 역기구학에 의하여 그에 해당하는 각 다리의 관절각을 해석적으로 구하였다 . 이러한 관절각 데이터를 상기 로봇의 ADAMS 모델에 적용하여 컴퓨터 시뮬레이션을 수행한 결과 , 계획된 걷기 및 속보 걸음새가 동력학적으로 안정함을 확인하였다 . 그러나 그 이전의 속보 패턴의 경우에는 시뮬레이션 결과와는 달리 실험 중 불안정한 거동을 보였다 . 그에 따라 원인 분석을 하는 과정 중, 속보와 같은 동 보행의 경우 ZMP보다는 WSM의 개념을 적극적으로 활용하고 보행 주기를 최대한 단축시키는 것이 안정성 확보에 매우 중요함을 발견하였다 .주요어 : 기구학, 동적 안정성, 영 모멘트 점, 확장된 안정성 여유

A normalization based image affine estimation technique for computer vision

In this paper, we propose the estimation method for the image affine information for computer vision. The first estimation method is given based on the XYS image normalization and the second estimation method is based on the XSR image normalization. In addition, we show that rotation and aspect ratio information can be obtained using the central moments of both the original image and the sensed image. Finally, we propose the modified version of the normalization method so that we may control the size of the image. It turns out that the XYS method has much better performance than the XSR method for the image having the aspect ratio change

Precision Circular-path Walking of a Biped Robot with Consideration of Rotational Effects

ABSTRACT When biped robots make turns, the ability to walk stably and precisely along any circular path is crucial. In this context, inverse kinematics solutions are found for accurate gait realization, and new zero moment point(ZMP) equations are derived with respect to the cyclindrical coordinate system to facilitate generation of stable walking patterns. Then, appropriate steady and transitional walking pat-terns are both proposed in form of time functons. Subsequently, walking patterns for a path but of different speeds are generated using the functions and associated formulas, and preliminarily checked for stability based on the ZMP equations. Upon comparison of those cases, one can see how and when robots may fall down during circular walking. Finally, those patterns are put to test on the sample robot by ADAMS® along with the inverse kinematics solutions and a new balance control scheme compensating for insufficient stability particulary during the initial transition period. Test re-sults show that the robot can walk along the circular path as predicted at a resonably high speed despite the distributed mass and ground contact effects, validating effectiveness of the suggested approach.

Torsional Vibration Control of a Rotating Chamber Shaft System Using Electrorheological Fluid

It is reported that an intermittently rotating chamber system will improve the ratio of firepower to armament space in the case of mid-calibre automatic guns. However, the parallel index, which is a main component of the system, tends to be torsionally flexible due to the low lateral stiffness of cam followers on the index turret. This may cause the shaft system connecting the turret with the chamber prone to considerable residual torsional vibration so that serious misalignment problems occur during ammunition loading and firing processes. Herein, an electrorhelogical (ER) fluid actuator that can suppress such vibrations and the associated semiactive control algorithm are proposed. By mathematical modeling and computer simulations, the performance of the entire system is proved satisfactory.

Precision Circular Walking of Bipedal Robots

Whenever bipedal robots need to make turns, the ability to walk stably and precisely along a circular curve of an arbitrary radius will be quite beneficial. This motivates us to derive new Zero Moment Point (ZMP) constraint equations with respect to a rotating coordinate frame, seek appropriate dynamic gaits based on them, and address the forward and inverse kinematics. After the relevant body and feet trajectories are fully prescribed, joint motions are determined using the inverse kinematics. A set of dynamic walking patterns including the transient are herein proposed and applied to an exemplificative case of turning locomotion. Conclusively, dynamic simulations prove the patterns to be successful even in the presence of distributed-mass and ground contact effects.Copyright

Design and Dynamic Behavior Prediction of a 4-DOF Piping Joint

In the building process of FPSOs(floating production, storage and offloading units) is the increasing demand of high performance piping joints that can be installed on its turret system and maintain smooth and long-term flow of ultra-high pressure crude oil, being subjected to external excitations such as wind and wave on the sea. Following such a trend, in this paper, a new-type piping joint of four effective degrees of freedom has been designed, and its dynamic characteristics predicted through mathematical modeling and computer simulations. Moreover, via an example it was shown how the yaw motion in particular can be independently controlled for future durability test despite strong kinetic couplings.

Discrete-Time Circular Walking Pattern for Biped Robots

When biped robots make turns fast, they may fall due to the action of centrifugal force. This is why one needs to consider the Zero Moment Point (ZMP) equations with respect to cylindrical coordinate system. Those ZMP equations are, however, so coupled and highly nonlinear even for the simple inverted pendulum model that it is hard to find a closed-form solution. Therefore, in this paper, they have been converted through temporal discretization to difference equations that admit numerical solution by most on-board computers. Thus-obtained walking patterns have been characterized and applied to several cases of different speed for comparison purposes. In so doing, the steady patterns have been blended with a type of transitional patterns to change the walking speed in the beginning and/or mid course of walking. Finally, those combined patterns have been put to test on a multi-body robot model by ADAMS®. Test results show that the robot could walk along a sample circular path as predicted at rapid speeds despite some modeling error, distributed mass and ground contact effects, validating efficacy of the suggested approach.

Vibration Analyses of HDD Spindle Systems Supported by Hydrodynamic Bearings Taking into Account Stator`s Flexibility

This paper presents vibration analyses of hard disk drive (HDD) spindle systems based on the finite element method. The systems under investigation have a cantilevered shaft rotating on hydrodynamic bearings. In particular, the influence of stator`s flexibility on major modes has been taken into account in dual ways lumped and distributed-parameter model approfches. Even the latter employs relatively macroscopic elements instead of extremely fine ones Popular in commercial codes. In order to prove the effectiveness of such formulated models, two types of HDD prototypes featuring different hub and stator structures are selected as examples. Compared to the first, the second type has a reinforced stator that would raise the natural frequency of the hub`s translational (or sideway) mode. Both free and forced vibration characteristics are computed, and subsequently compared with the experimental data. It is our conclusion that Particularly the Proposed distributed model method is an efficient design tool for state-of-the-art HDD spindle systems.

Vibration Control of Flexible Rotor Systems Using an Electro-rheological Fluid Damper

This paper concerns the design and application of an electro-rheological (ER) fluid damper to semiactive vibration control of rotor systems. In particular, the system under present study is constructed structurally flexible in order to explore multiple critical speeds within operation range. To this end, the dynamic models of the proposed ER damper and its associated amplifier are derived in the first place. Subsequently entire rotor system model is assembled along with the dynamics of the end effector based on a finite element method enabling prediction as to its free and forced vibration characteristics. Next, an artificial intelligent (AI) feedback controller is synthesized taking into account the peculiarity of Coulomb damping effect in rotor applications. Finally, computational and experimental results are presented including model validation and control performances. In practice, such an AI control proved effective whether the spin speed was either before or after critical speeds.