Fan Jizhuang

Foot trajectory planning of frog swimming based on propulsion mechanism

To provide reasonable reference trajectories for frog inspired robot, the bionic trajectory generation was studied in this paper. Though joint trajectories vary with different motion modes, joint speeds are too fast and tuned with the musculoskeletal system. However, mechanical structures of bionic robot are simplified and diver abilities limit the speed, so the method to generate joint trajectories which not only reflect the characteristics of real frog swimming but also are within the limitation of drivers were proposed in this paper. Firstly, swimming mechanism of frog was briefly introduced to analyze motion patterns of hind limbs and webbed feet. Secondly, trajectory (relative to body) planning was divided into hind limb planning and webbed foot planning. Hind limb trajectory planning was conducted via end track planning and acceleration planning, while acceleration planning was operated for webbed foot planning. Then, trajectories could be operated from fast to slow by adjusting duration time of the planned trajectories. Finally, the trajectories were used as input of hydrodynamic simulation to validate the trajectory planning method.

An experiments based modeling method for Pneumatic Artificial Muscle

The Pneumatic Artificial Muscle (PAM) provides many advantages over conventional actuators, especially pneumatic cylinders. It provides light weight, simple structure, high output force to weight ratio, low cost and so on. Despite of these advantages, there are also challenges in using a PAM actuator, such as the behavior of nonlinearity and high hysteresis. To get optimum design and usage, it is significant to find a good way to model the PAM. In this paper, an experiments based modeling method for pneumatic artificial muscle is proposed. This model is a polynomial model and the form of results is simple. At the same time, the parameters are easy to be obtained. Validation experiments are carried out in this paper. The experimental results show the feasibility and correctness of this method. Meanwhile, its simple structure is convenient for further design of PAM control system.

Virtual space painting system based on transparency haptic interaction

The traditional drawing system based on the 2-D mouse can not realize the haptic interaction between operators and virtual environment. This is not available for operator to feel the interaction sensitivity. A virtual space painting system based on transparency haptic interaction is proposed. This system uses the admittance type haptic device as the information interaction interface between operators and virtual environment. This paper presents an implicit force control algorithm to adapt the control of the transparency haptic interaction device. This system use the body contact detection, the virtual force generation and smoothness to build the virtual environment. Finally, a virtual painting experiment is done. The result shows that this system could improve the transparency of the haptic interaction. It means that the real artistic creation could be realized on the computer.

Propulsive efficiency of frog swimming with different feet and swimming patterns

ABSTRACT Aquatic and terrestrial animals have different swimming performances and mechanical efficiencies based on their different swimming methods. To explore propulsion in swimming frogs, this study calculated mechanical efficiencies based on data describing aquatic and terrestrial webbed-foot shapes and swimming patterns. First, a simplified frog model and dynamic equation were established, and hydrodynamic forces on the foot were computed according to computational fluid dynamic calculations. Then, a two-link mechanism was used to stand in for the diverse and complicated hind legs found in different frog species, in order to simplify the input work calculation. Joint torques were derived based on the virtual work principle to compute the efficiency of foot propulsion. Finally, two feet and swimming patterns were combined to compute propulsive efficiency. The aquatic frog demonstrated a propulsive efficiency (43.11%) between those of drag-based and lift-based propulsions, while the terrestrial frog efficiency (29.58%) fell within the range of drag-based propulsion. The results illustrate the main factor of swimming patterns for swimming performance and efficiency. Summary: To explore propulsion in swimming frogs, this study analyzed mechanical efficiencies based on data describing aquatic and terrestrial feet and swimming patterns.