Detail Cantuman

Analysis of local-camera-based shepherding navigation
Y. Tsunoda , Y. Sueoka, Y. Sato and K. Osuka
Depar tment of M echanical Engineering, Graduate S chool of Engineering, Osak a Universit y, Osak a, Japan
ABSTR AC T
This study investigates group navigation with the aid of strong interaction between two kinds of agents: A shepherd drives a sheep group with a large population to a given goal position. Even though numerous studies have been performed on the realization of shepherd-like navigation, they are based on the condition that all sheep positions are given. This study examines the navigation of a sheep group using a local-camera-based approach, i.e. a shepherd perceives sheep using the shepherd’s vision. Before testing local-camera-based navigation, we design a shepherd controller referred to as a farthest-agent targeting controller, in which the shepherd selects the sheep farthest from the goal. We demonstrate the validity of the proposed controller using statistical analysis and comparison with previous conventional controllers. After examining the effectiveness of this con troller, we show that the controller works appropriately even if the shepherd cannot know all sheep positions. In addition, we show the robustness of the proposed controller for the positional errors of the sheep flock or for agent-lost cases to apply it to real-world situations.
KEY WORDS
Large group navigation; local- camera based approach; s hepherd-like s t rate g y

Key design parameters of a few types of electro-hydrostatic actuators for
humanoid robots
Tianyi Ko , Hiroshi Kaminaga and Yoshihiko Nakamura
Depar tment of M echano -I nformatics, Graduate S chool of I nformation S cience and Technology, The Universit y of Tok yo, Tok yo, Japan
ABSTR AC T
To overcome the tradeoff between the bandwidth and force-to-weight ratio of the backdrivable actuators, actuation by electro-hydrostatic actuators (EHA) is effective. Based on the idea, we developed the adult size, humanoid robot ‘Hydra’, whose joints are driven by EHA. In its development, a critical problem was the insufficient force of the available lightweight and backdrivable EHA. In this paper, we present our approach to enhance their maximum force while keeping them small, lightweight and backdrivable. We first analyze the behavior of EHA and show that the maximum force is enabled on the balance between the viscous loss and the internal leakage loss. We also show that miniaturization of the actuator moves the system to the internal leakage loss dominant side, and to encounter this, reduction of the internal gap, maintain of the fluid viscosity, and full utilization of the space to enlarge the pressure receiving surface are effective. The mechanical design process and experimental evaluation on each of these three aspects are detailed.
KEY WORDS
Ac t u ato r ; EH A ; hyd rau l i c ; fo rce control; back drivabilit y

The effects of variable mechanical parameters on peak power and energy
consumption of ankle-foot prostheses at different speeds
Dianbiao Donga,b, Bryan Convensb, Yuanxi Suna, Wenjie Gea, Pierre Cherelleb and Bram Vanderborghtb
aSchool of Mechanical Engineering, Northwestern Polytechnical University, Xi’an, People’s Republic of China; bDepartment of Mechanical Engineering, Vrije Universiteit Brussel, Brussels, Belgium
ABSTR AC T
In recent years, powered ankle-foot prostheses are developed to restore human ankle behaviour. Compared with common passive ankle prostheses, a powered ankle-foot prosthesis can provide amputees with better performance on walking gait by providing additional energy. However, the electrical peak power of powered ankle-foot prostheses at high speed is still a big challenge for the current actuation system. While most researchers focus on the energy consumption on one walking speed, we investigate the influences of several variable mechanical parameters to reduce electrical peak power during different locomotion speeds. Then we apply this concept to current ankle-foot models. It’s found that the variable mechanical parameters can significantly reduce the demand of electrical peak power at different speeds. Meanwhile, the reduction of the electrical peak power does not lead to a large increment of the energy consumption. The results also show that every variable mechanical parameter has a different influence on the peak power and energy consumption of the ankle-foot prosthesis. It means the most effective and sensitive variable mechanical parameter need to be found for a specific ankle prosthesis system.
KEY WORDS
Ankle-foot prosthesis; variable stiffness; electrical power; energy consumption; optimization