Practical high curvature path planning algorithm in joint space

Delgado, Raimarius,Byoung Wook Choi IET 2015 Electronics letters Vol.51 No.6

<P>A practical high curvature path planning algorithm that considers the velocity limit of a mobile robot in joint space is proposed. The existence of obstacles that constrict the smooth movement of mobile robots is inevitable. To avoid incoming collision, the robot is redirected to a new path with respect to the dimensions of the obstacle and a safety factor. The redirected path consists of geometric constraints such as high curvatures on its turning points which cause difficulty in controlling the mobile robot. Thus, a central velocity generation method that considers both velocity limits through a convolution operator and high curvatures at turning points is suggested. The central velocity is able to be within the configured velocity limit, otherwise actual velocity commands in joint space could result. Therefore, interpolation to obtain uniform sampling and velocity downscaling is performed to generate a feasible joint space trajectory. The result shows short travelling time compared with previous methods while satisfying velocity limits in the joint space.</P>

A Probabilistic Analysis for Periodicity of Real-time Tasks

Raimarius Delgado,Byoung Wook Choi 한국인터넷방송통신학회 2021 International Journal of Internet, Broadcasting an Vol.13 No.1

This paper proposes a probabilistic method in analyzing timing measurements to determine the periodicity of real-time tasks. The proposed method fills a gap in existing techniques, which either concentrate on the estimation of worst-case execution times, or do not consider the stochastic behavior of the real-time scheduler. Our method is based on the Z-test statistical analysis which calculates the probability of the measured period to fall within a user-defined standard deviation limit. The distribution of the measured period should satisfy two conditions: its center (statistical mean) should be equal to the scheduled period of the real-time task, and that it should be symmetrical with most of the samples focused on the center. To ensure that these requirements are met, a data adjustment process, which omits any outliers in the expense of accuracy, is presented. Then, the Z-score of the distribution according to the user-defined deviation limit provides a probability which determines the periodicity of the real-time task. Experiments are conducted to analyze the timing measurements of real-time tasks based on real-time Linux extensions of Xenomai and RT-Preempt. The results indicate that the proposed method is able to provide easier interpretation of the periodicity of real-time tasks which are valuable especially in comparing the performance of various real-time systems.

RTSP를 이용한 임베디드 하드웨어 기반 동시 방송 시스템 개발

Raimarius Delgado,이승형(Seung-Hyung Lee),안병덕(Byung-Dug Ahn),최병욱(Byoung Wook Choi) 한국지능시스템학회 2018 한국지능시스템학회논문지 Vol.28 No.4

자연 재해의 증가는 다양한 방식으로 우리의 생활 방식을 변화시키고 있다. 본 논문에서는 이러한 재난 상황에서 경보에 사용될 수 있는 임베디드 플랫폼 기반의 오디오 동시 방송 시스템을 구현하였다. 이 시스템은 네트워크에 연결된 여러 클라이언트에 오디오 신호를 전송하는 서버로 구성된다. 실제 미디어 전달은 실시간 전송 프로토콜인 RTSP(real-time streaming protocol)에 캡슐화 된 실시간 프로토콜 RTP(real-time protocol) 스트림 개념을 사용하여 구현되어 미디어 전송을 제어하고 각 구성 요소 간의 데이터 전송을 보장한다. 서버 및 클라이언트는 하드웨어 오디오 코덱을 포함한 임베디드 플랫폼으로 개발되었다. ALSA(Advanced Linux Sound Architecture)를 사용하는 장치 드라이버는 하드웨어 코덱을 구동하고 아날로그 오디오 신호와 디지털 신호의 변환을 위하여 개발되었다. 오픈 소스 라이브러리는 서버와 클라이언트에서 구현되어 RTSP와 RTP를 이용한 데이터 교환을 지원한다. 임베디드 환경에서 뮤 법칙 알고리즘을 사용하여 전송 손실과 딜레이를 해결하였고, 유니캐스트 및 멀티캐스트 스트리밍 방식으로 개발된 시스템의 실용성을 검증하는 실험을 수행하였다. Increasing occurrence of natural disasters lead to changes in our lifestyle in various ways. This paper presents a simultaneous audio broadcasting system based on an embedded platform that can be used in disaster warning applications. The system consist of a server that streams audio signals to different clients connected within a network. The actual media delivery is implemented using real-time protocol (RTP) stream concept encapsulated into real-time streaming protocol (RTSP) to control media transmission and ensure transmission of data between each component. We develop embedded platforms, with attached hardware audio codec, as streaming server and clients. Device driver using Advanced Linux Sound Architecture (ALSA) is developed to operate the hardware codecs and convert analog audio signals to digital signals and vice versa. Open source libraries are implemented in the server and clients to support data exchange using RTSP and RTP. Transmission loss and delay were solved in the embedded environment using μ-law. Experiments are performed in unicast and multicast streaming to validate the practicality of the developed system.

복제방지 칩을 이용한 임베디드 기반 보안 제어기

박재호(Jaeho Park),Raimarius Delgado,이천호(Cheonho Lee),최병욱(Byoung Wook Choi) 한국지능시스템학회 2018 한국지능시스템학회논문지 Vol.28 No.5

본 논문에서는 임베디드 제어 장치에 있어서 악의적 프로그램으로부터 시스템을 보호하기 위하여 복제방지칩을 이용한 보안제어기를 제안한다. 보안 제어 방법은 사용자 프로그램과 복제방지 칩이 동일한 암호화 방식을 사용하는지 비교하며, 프로그램에서 복제방지 칩으로 데이터를 송신하면 복제방지 칩에서는 수신된 데이터를 암호화하여 반환해준다. 이후 프로그램이 전송하기 전의 데이터를 암호화해서 칩으로부터 반환받은 데이터와 비교해서 일치할 경우에만 프로그램이 정상적으로 실행되고 일치하지 않을 경우나 이러한 과정을 수행하지 않을 경우 프로그램은 종료된다. 또한 복제 방지 칩을 강제로 변경하거나 제거하는 하드웨어 해킹을 방지하기 위해 부팅 초기 단계인 부트로더에서 복제방지 칩이 정상적으로 연결되어 있고 칩이 변경되지 않은 경우에만 부팅과정을 진행한다. 실험에서는 부팅 시 복제방지 칩을 제거할 경우 부팅이 되지 않고, 운영체제가 인증과정이 실패하거나 인증과정을 수행하지 않는 프로그램의 실행을 차단할 수 있다는 것을 보여 준다. 이러한 결과를 바탕으로 임베디드 시스템에서 복제방지 칩을 이용한 보안제어기를 사용해서 시스템을 보호할 수 있음을 검증하였다. In this paper, we propose a security controller using a copy protection chip to protect system from malicious programs in the embedded controller. The security control method compares whether user program and the copy protection chip use the same encryption method. When the program transmits data to the copy protection chip, the copy protection chip encrypts and returns the received data. After that, the program encrypts the data before transmission and compares it with the data returned from the chip. If the data encrypted by the program matches the data returned by the chip, the program is executed. However, if the data does not match or the authentication process is not performed, the program is terminated. In addition, to prevent hardware hacking that forcedly changes or removes the copy protection chip, the boot process proceeds only if the copy protection chip is normally connected at boot time and the chip is not changed. The experiment shows that booting with no copy protection chip is not possible, and the operating system can block the execution of the program which does not perform or fails authentication process. Based on these results, we verified that the system can be protected by using the security controller using the copy protection chip in the embedded system.

A Practical Joint-Space Trajectory Generation Method Based on Convolution in Real-Time Control

Yang, Gil Jin,Delgado, Raimarius,Choi, Byoung Wook SAGE Publications 2016 International Journal of Advanced Robotic Systems Vol.13 No.2

<P>This paper proposes a joint-space trajectory generation method for practical navigation with a high curvature path of mobile robots. A technique to generate central velocity commands using a convolution operator that considers only the physical limits of a mobile robot was discussed. In practical application, controlling the heading angles along a curved path is required and the existence of obstacles is inevitable. First, we suggested an algorithm that generates a trajectory to consider the heading angles along a smooth Bezier curve by redefinition of the curve parameter. However, the presence of an obstacle along the planned path requires redirection to a new path where geometrical limitations such as high curvature turning points exist, resulting in tracking error. We propose a method that manages a variation of linear interpolation to generate a feasible trajectory while conserving the high curvature path and the merits of convolution. Joint-space trajectories are produced by scaling down the generated central velocity through reduction of the given maximum velocity limit. We show through a simulation example that the proposed method is able to generate a trajectory that can accurately track a planned path on a designed platform based on actual parameters. Finally, an experiment is successfully conducted on a two-wheeled mobile robot, Tetra DS-III, in a real-time control system. The experiment results display distinct advantages in the criteria of time optimality and periodicity of control tasks, while conserving all possible limitations that could occur during navigation compared with previous studies.</P>

미세수술로봇의 작업 효율성 증가를 위한 적응형 모션 스케일링

김건욱(Geon Uk Kim),라이마리우스 델가도(Raimarius Delgado),정혜원(Hae Won Jeong),인용석(Yong Seok Ihn) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.5