Research On A Frog-inspired Soft Jumping Robot Driven By Combustion

The jumping robot has the potential to work in complex terrain due to its excellent obstacle-crossing ability and has broad application prospects.Jumping movement is one of the typical movement forms of frogs on land.It is of considerable significance to analyze the frog jumping mechanism and develop a frog-like jumping robot.At present,most frog-inspired jumping robots use motors or pneumatic muscles to actuate jumping directly or store energy for jumping movements,which results in a robot with a complicated structure and heavyweight.In this paper,explosive actuation with high energy density and light-weighted soft actuators are used to design a miniaturized froginspired robot that can achieve directional jumping.In this paper,the structure design of the robot is firstly carried out,including the pneumatic soft rotating joint applied to the robot's forelegs,the combustion-driven soft actuator,and the rigid four-bar linkage structure applied to the hind limbs.Pneumatic soft rotating joints imitate the forelimbs of frogs,which play the role of adjusting the robot's jumping angle and buffering when landing.Using the Yeoh material model and the principle of virtual work,the mathematical model of the relationship between rotation angle and driving air pressure is established.As the "muscle" of the robot,the explosive soft actuator is the energy supply unit for its jump movement.The four-bar linkage of the hind limbs is actuated during the combustion-and-expansion process,and transmits the explosive force to the ground effectively.The dimension parameters of the four-bar linkage mechanism were optimized using MATLAB to make the movement trajectory of the end of the hind limb,that is,the robot foot,approximate a straight line.The production of the above soft actuators integrates 3D printing and casting technologies.To achieve a stable and controllable combustion acutation,a miniaturized gaseous fuel supply device weighing only 61.8g is designed,which can achieve the gas generation and delivery with high precision.Utilizing the pyrolysis property of solid energy storage materials to generate hydrogen and oxygen for combustion driving,two fuel generating chambers are provided in the fuel supply device to control the decomposition reaction by controlling the temperature in the chamber.Besides,a high-precision gas flow control method based on pressure sensors is proposed,which can achieve high-precision multigas delivery by combining solenoid valves and air pumps.Experiments have shown that the accuracy of gas delivery is ±0.1ml when the volume does not exceed 50 ml.The quasi-static experiments of elastic potential energy and work efficiency of the combustion-driven soft actuator are conducted with the change of the driving air pressure.The explosive actuation performance and the actuator efficiency with the relationship of the volume and ratio of combustible gases and the mass of loads are analyzed through experiments.Propose a method to improve explosive efficiency according to the weight of load by using the selected volume of combustion chamber and ratio of fuel.The work performance of the explosive actuator is consistent(the error is about 11%),and the efficiency can reach 8.9%.Finally,the robot assembly was completed,and the center of gravity adjustment mechanism whose effectiveness was verified in ADAMS is designed to make the robot obtain a stable jumping attitude.The equivalent actuating force of the explosive actuation is set in ADAMS,under which,the robot obtained an initial velocity about 2.7m/s,and the peak forces of the hind limb driving rod and the robot feet are about 105 N and 74 N respectively.Stable simulation jumping can be achieved under the take-off angles of 45°,55° and 65°.