Research On The Frog Inspired Robot And Its Swimming Trajectory Planning

With the development of ocean resource exploration and military strategy,amphibious robots which can adapt to complex work environment and mission requirements are in dire need to perform a variety of tasks which are near ocean terrain and human can not complete.Therefore,it is of great practical value and practical significance to develop amphibious robot which can adapt to the amphibious terrain of land and beach.Frogs have excellent amphibious athletic ability,although their underwater swimming performance and efficiency is inferior to the fishes propulled by the use of pectoral fin swing and caudal fins,but it is the biggest highlight of the frog that they can combine underwater swimming and ground jump function by the same leg structure to achieve smart amphibious movement.At present,the research on the jumping function of the frog robot is relatively more,and the application of the frog swimming mechanism in the robot is less.Therefore,the frog inspired robot and its swimming trajectory planning are studied,which lays the foundation for the development of bionic frog amphibious robot.It is the basis of studying the bionic frog robot by observing the swimming process of biological frog and extracting the trajectory.According to the motion data collected from the observation experiment,the movement pattern analysis of the terrestrial frog and the aquatic frog is needed to study the hydrodynamic force in the frog swimming mechanism.The fluid simulation software FLUENT based on computational fluid dynamics(CFD)is used to solve the frog s elf propulsion swimming simulation and the problem of hydrodynamics.To research the propulsive mechanism and its efficiency in terms of lift and drag components of the thrust,the palm moving patterns and the flow field information near the frog were analyzed,laying the foundation for the following research and trajectory planning of the frog inspired robot.The CFD method can solve the palm hydrodynamic forces,but it has the disadvantages of bad computing stability,low computing efficiency,long runnin g time,et al,making it not suitable for design optimization or other conditions involving online computing.Therefore,the hydrodynamic force was divided into quasi steady force and added mass force to quickly compute the palm thrust via theoretical fluid mechanics.The frog inspired robot model was optimized according to the dynamic equations.The pneumatic muscle was used as the driver.The high speed switch valve was utilized to control the pneumatic system and the frog inspired robot integrating the electrical,pneumatic and mechanical systems was designed.The trajectory planning method based on the palm moving space was studied according to the swimming mode characteristics and swimming mechanism in propulsive phase to generate a trajectory reflecting frog motion patterns and fitting for the driver,which can guide robot swimming experiments.This method simulates the biological frog trajectory by track planning and acceleration planning of the palm,and can be applied into robot.Therefore,the robot trajectory can reflect the swimming characteristics of the real frog and satisfy the driver limit to guide the following study of control system.According to the analysis of the frog swimming mechanism,the trajectory optimization is carried out from the palm acceleration during the propulsion phase,the trajectory is planned according to the minimum resistance in the recovery phase and the trajectory of the whole swimming cycle is therefore obtained.In order to test the robot design and the trajectory planning results,it is necessary to study the control problem of the bionic frog robot.The duty cycle of the PWM of the high speed switch valve is set as the pneumatic muscle stimulus signal.The robot musculoskeletal system model was obtained by built th e model between joint angle and stimulus signal including the muscle dynamic model,joint model and pneumatic model.According to the characteristics of the joint driver during frog swimming,the control method based on the musculoskeletal system model and fuzzy PID control method were used to control the joint and accomplish the swimming experiments.Finally,the robot experiment platform is designed including a micro controller in body,sensors to extract data and wireless communication unit to sending da ta and commends.The robot swimming experiments in water verified the rationality of the design of the robot,the feasibility of the control system and the corr ectness of trajectory planning.