Safe Arm Using Compliant Hybrid Joints for Mobile Manipulators in Human-Symbiotic Environments

Zhijun Li,Aiguo Ming,Ning Xi,Jiangong Gu,Makoto Shimojo 한국과학기술원 인간친화 복지 로봇 시스템 연구센터 2005 International Journal of Assistive Robotics and Me Vol.6 No.1

  In this paper, a safe arm with compliant hybrid joints for human-friendly service robots is presented, which realizes human safety, absorbing impact force, and task fulfillment. The robot is composed of links covered with soft materials and hybrid joints, which can be put into active or passive mode as needed. In an unexpected or expected collision with human, the arising impulse force is attenuated effectively by the physical model, which is developed with hybrid joints and soft covering. Owing to the displacement of the links when the joint is passive, a recovery control algorithm has been developed for the end-effector to maintain its desired task position after the collision. The force attenuation property has been verified through collision experiments in that the capability of the proposed passive arm in overcoming the limitations of active compliance control has been demonstrated. Simulation results also showed that the proposed control method is useful for robot"s task fulfillment as well.

Survey on Security in Wireless Sensor

Zhijun Li,Guang Gong 한국정보보호학회 2008 정보보호학회논문지 Vol.18 No.6

Advances in electronics and wireless communication technologies have enabled the development of large-scale wireless sensor networks (WSNs). There are numerous applications for wireless sensor networks, and security is vital for many of them. However, WSNs suffer from many constraints, including low computation capability, small memory, limited energy resources, susceptibility to physical capture, and the lack of infrastructure, all of which impose unique security challenges and make innovative approaches desirable. In this paper, we present a survey on security issues in wireless sensor networks. We address several network models for security protocols in WSNs, and explore the state of the art in research on the key distribution and management schemes, typical attacks and corresponding countermeasures, entity and message authentication protocols, security data aggregation, and privacy. In addition, we discuss some directions of future work.

Data Delivery based on Mobile Roadside Unit and with QoS Guarantee for Vehicular Ad Hoc Networks

Li Chen,Zhijun Li,Shouxu Jiang 보안공학연구지원센터 2013 International Journal of Future Generation Communi Vol.6 No.5

System identification of the suspension tower of Runyang Bridge based on ambient vibration tests

Zhijun Li,Dongming Feng,Maria Q. Feng,Xiuli Xu 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.19 No.5

A series of field vibration tests are conducted on the Runyang Suspension Bridge during both the construction and operational stages. The purpose of this study is devoted to the analysis of the dynamic characteristics of the suspension tower. After the tower was erected, an array of accelerometers was deployed to study the evolution of its modal parameters during the construction process. Dynamic tests were first performed under the freestanding tower condition and then under the tower-cable condition after the superstructure was installed. Based on the identified modal parameters, the effect of the pile-soil-structure interaction on dynamic characteristics of the suspension tower is investigated. Moreover, the stiffness of the pile foundation is successfully identified using a probabilistic finite model updating method. Furthermore, challenges of identifying the dynamic properties of the tower from the coupled responses of the tower-cable system are discussed in detail. It\'s found that compared with the identified results from the freestanding tower, the longitudinal and torsional natural frequencies of the tower in the tower-cable system have changed significantly, while the lateral mode frequencies change slightly. The identified modal results from measurements by the structural health monitoring system further confirmed that the vibrations of the bridge subsystems (i.e., the tower, the suspended deck and the main cable) are strongly coupled with one another.

Robust Adaptive Motion Control for Underwater Remotely Operated Vehicles with Velocity Constraints

Zhijun Li,Chenguang Yang,Nan Ding,Stjepan Bogdan,Tong Ge 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.2

In this paper, robust adaptive control strategies are designed for Underwater Remotely Operated Vehicles (ROVs) with velocity constraints. First, robust control strategies are investigated for under-water ROVs, and then adaptive robust control strategies are further developed with online parameter estimation. To prevent the velocity constraint violation, the Barrier Lyapunov Function (BLF) is employed in Lyapunov synthesis. By ensuring the boundedness of the BLF, we also guarantee that the velocity constraints are not transgressed. The stability analysis of the closed-loop system is provided and all closed-loop signals are ensured to be bounded. Simulation results for 5 degree-of-freedom (DOF) underwater ROV demonstrate the effectiveness of the proposed approach.

Effect of boundary conditions on modal parameters of the Run Yang Suspension Bridge

Zhijun Li,Aiqun Li,Jian Zhang 국제구조공학회 2010 Smart Structures and Systems, An International Jou Vol.6 No.8

Changes in temperature, loads and boundary conditions may have effects on the dynamic properties of large civil structures. Taking the Run Yang Suspension Bridge as an example, modal properties obtained from ambient vibration tests and from the structural health monitoring system of the bridge are used to identify and evaluate the modal parameter variability. Comparisons of these modal parameters reveal that several low-order modes experience a significant change in frequency from the completion of the bridge to its operation. However, the correlation analysis between measured modal parameters and the temperature shows that temperature has a slight influence on the low-order modal frequencies. Therefore, this paper focuses on the effects of the boundary conditions on the dynamic behaviors of the suspension bridge. An analytical model is proposed to perform a sensitivity analysis on modal parameters of the bridge concerning the stiffness of expansion joints located at two ends of bridge girders. It is concluded that the boundary conditions have a significant influence on the low-order modal parameters of the suspension bridge. In addition, the influence of vehicle load on modal parameters is also investigated based on the proposed model.

Effect of boundary conditions on modal parameters of the Run Yang Suspension Bridge

Li, Zhijun,Li, Aiqun,Zhang, Jian Techno-Press 2010 Smart Structures and Systems, An International Jou Vol.6 No.8

Changes in temperature, loads and boundary conditions may have effects on the dynamic properties of large civil structures. Taking the Run Yang Suspension Bridge as an example, modal properties obtained from ambient vibration tests and from the structural health monitoring system of the bridge are used to identify and evaluate the modal parameter variability. Comparisons of these modal parameters reveal that several low-order modes experience a significant change in frequency from the completion of the bridge to its operation. However, the correlation analysis between measured modal parameters and the temperature shows that temperature has a slight influence on the low-order modal frequencies. Therefore, this paper focuses on the effects of the boundary conditions on the dynamic behaviors of the suspension bridge. An analytical model is proposed to perform a sensitivity analysis on modal parameters of the bridge concerning the stiffness of expansion joints located at two ends of bridge girders. It is concluded that the boundary conditions have a significant influence on the low-order modal parameters of the suspension bridge. In addition, the influence of vehicle load on modal parameters is also investigated based on the proposed model.

On Motion Optimization of Robotic Manipulators with Strong Nonlinear Dynamic Coupling using Support Area Level Set Algorithm

Zhijun Li,Kun Yang,Stjepan Bogdan,Bugong Xu 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.6

Aiming for a better dynamic performance from the robot beyond the physical limits set by the manufacturers, in this paper we propose to integrate the robot dynamics into motion planning and then to approximate the robot joint torques using parameterized B-splines. By introducing a high-dimensional non-linear fitness function, we transform the motion planning problem into an optimiza-tion of a non-linear fitness function, and then we develop the approach based on Support Area Level Set Algorithm (SALAS). It integrates dual-stage sampling strategies to avoid early convergence in a small search field and to improve the rate of convergence to the potential solution. The effectiveness of the proposed approach has been verified by the simulation of a two-link robotic manipulator.

Survey on Security in Wireless Sensor

Li, Zhijun,Gong, Guang Korea Institute of Information Security and Crypto 2008 정보보호학회논문지 Vol.18 No.b6

Advances in electronics and wireless communication technologies have enabled the development of large-scale wireless sensor networks (WSNs). There are numerous applications for wireless sensor networks, and security is vital for many of them. However, WSNs suffer from many constraints, including low computation capability, small memory, limited energy resources, susceptibility to physical capture, and the lack of infrastructure, all of which impose unique security challenges and make innovative approaches desirable. In this paper, we present a survey on security issues in wireless sensor networks. We address several network models for security protocols in WSNs, and explore the state of the art in research on the key distribution and management schemes, typical attacks and corresponding countermeasures, entity and message authentication protocols, security data aggregation, and privacy. In addition, we discuss some directions of future work.

Survey on Security in Wireless Sensor

Zhijun Li,Guang Gong 한국정보보호학회 2008 정보보호학회논문지 Vol.18 No.b6

Advances in electronics and wireless communication technologies have enabled the development of large-scale wireless sensor networks (WSNs). There are numerous applications for wireless sensor networks, and security is vital for many of them. However, WSNs suffer from many constraints, including low computation capability, small memory, limited energy resources, susceptibility to physical capture, and the lack of infrastructure, all of which impose unique security challenges and make innovative approaches desirable. In this paper, we present a survey on security issues in wireless sensor networks. We address several network models for security protocols in WSNs, and explore the state of the art in research on the key distribution and management schemes, typical attacks and corresponding countermeasures, entity and message authentication protocols, security data aggregation, and privacy. In addition, we discuss some directions of future work.