| With the continuous construction of urbanization,small-scale earthworks in urban construction are also increasing.The small excavator is very suitable under urban construction environment which has large population density and complex traffic situations due to its flexible mobility,versatile functions and so on.As a result,small excavator becomes an indispensable construction machinery in urban construction.Nevertheless,most of the construction machinery takes the diesel engine as power source and the hydraulic system as working equipment controller,which has not only high energy consumption and exhaust pollution problems,but also working noise and strong vibration problems.In addition,the reliability of hydraulic system is quite susceptible to the operating environment,and the maintenance is also very complex.Meanwhile,the manufacturing cost of hydraulic precision components is expensive,and some of its core components still dependents on imports.All the situations above are the reasons that constrained the technological development and market promotion of small excavators.Aiming at these existing problems of hydraulic excavator,this paper takes excavator as the object of study and presents a noval excavating mechanism with metamorphic functions,which uses servo motor and linear actuator as power source,and from the objective of reducing the number of driving sources and compacting the structure of the excavator,this paper presents a kind of locking-metamorphism method.In addition,replacing the hydraulic cylinder with linear actuator,on the one hand,linear actuator can effectively solve the high energy consumption and exhaust pollution problems of traditional excavator,on the other hand,also eliminates the complex hydraulic piping system,thoroughly solves the leakage problem,which makes maintenance more convenient.The specific contents of this paper include the following aspects:(1)Based on the graph theory,the configuration synthesis of the traditional excavator is investigated,and the optimum scheme is selected and optimized from 78 topologies.For the purpose of reducing the number of driving sources,a kind of locking-metamorphism method is presented.At last,the novel metamorphic excavator mechanism of this paper is constructed,and its 3D model is established.Investigations on topological changes of the mechanism are carried out via adjacency matrix,each structural form's degrees of freedom is calculated,and each structural form's motion is illustrated by diagram.(2)The kinematic model of each structural form is established by the closed-loop vector method,and forward and inverse kinematic equation is obtained.The correctness of kinematic model is verified by comparing analytic solutions of kinematic equation with solutions of Creo simulation.(3)The working condition which includes full bucket lifting working condition,bucket rod excavating working condition and shovel bucket excavating working condition of the mechanism is analyzed using the Lagrange's equation.Taking YC08-8's working parameters as the reference,the linear actuator driving force expression is obtained using the kinetic equation.(4)Based on the transient structural of ANSYS Workbench,the mechanism is simplified as a rigid-flexible coupled multi-body system,and its transient dynamic analysis is made under the impact load.The excavation conditions are decomposed into two measures:Bucket rod excavating working condition and Shovel bucket excavating working condition.Then under the impact load,the stress-time curves of the whole structure and the stress nephogram of the key structures and the thrust-time relationship curve of linear actuators are obtained under the two working conditions. |
PDF Full Text Request