Currently,virtual assembly technology has attracted increasing attention due to considerations of solving assembly problems in virtual environment before actual assembly in manufactory.Previous studies on kinematic analysis of mechanism only aim at analyzing motion law of single mechanism,but can not simulate the multi-mechanisms motion process at the same time,let alone simulating the automatic assembly process of products in a whole assembly workshop.In order to simulate the assembly process of products in an assembly workshop and provide effective data for analyzing mechanical performance after finishing assembly simulation in virtual environment,this study investigates the kinematics analysis of mechanisms based on virtual assembly.Firstly,in view of the same function of the kinematic pairs and the assembly constraints on restricting the motion of components(subassembly or part),the method of identifying kinematic pairs automatically based on assembly constraints is presented.The information of kinematic pairs can be obtained through calculating the constraint degree of the assembly constraints.Secondly,the incidence matrix eliminating element method is proposed in order to search the information and establish the models of mechanisms automatically after finishing assembly simulation in virtual environment.Both methods have important significance for reducing the workload of pretreatment and promoting the level of automation of kinematics analysis.Finally,the method of kinematics analysis of mechanisms is presented.Based on Descartes coordinates,three types of kinematics equations are formed.The parameters,like displacement,velocity,and acceleration,can be obtained by solving these equations.All these data are important to analyze mechanical performance.All the methods are implemented and validated in the prototype system virtual assembly process planning(VAPP).The mechanism models are established and simulated in the VAPP system,and the result curves are shown accurately.The proposed kinematics analysis of m
To analyze the spring disturbance torque caused by motional cable harness in a stabilized platform,the Kirchhoff theory based cable harness model has been previously developed to dynamically simulate the motional cable harness.In this paper,this model was validated by comparing the simulation results with the experiment results(both the spring force and the deformed profile of the motional cable harness).In the experiment,a special optical measuring instrument based on binocular vision was developed and the motion and deformation of cable harness were measured.A simplified stabilized platform system was constructed,and the absolute value of spring disturbance force during the motion of this simplified frame was obtained by using a force gauge(0.02N precision).The physical parameters of experimental specimen were also measured.The experimental and simulated results showed good agreement.These results should be useful for better motional cable harness layout design and reliable evaluation of the spring disturbance torque.
In order to predict the flattening rate of the cross-section accurately during the tube bending,the generation principle,the solution and the influence factor of the cross-section flattening were studied.On the basis of the plane-stress and the assumption that the plastic volume is constant,three-dimensional strain formulas were established in consider of the cross-section flattening.Considering the wall-thickness change,the approximate calculation formulas of short axis flattening rate were deduced,with the outer diameter and the inner diameter as parameters.Because different materials have different cross-section flattening rates,a material correction factor was introduced to modify the formula based on experiments.Finally,the validity of the theoretical formulas was proved according to the calculation and the experiment results,which can provide a reference for the forming quality prediction in tube bending.
Assembly process planning(APP) for complicated products is a time-consuming and difficult work with conventional method.Virtual assembly process planning(VAPP) provides engineers a new and efficiency way.Previous studies in VAPP are almost isolated and dispersive,and have not established a whole understanding and discussed key realization techniques of VAPP from a systemic and integrated view.The integrated virtual assembly process planning(IVAPP) system is a new virtual reality based engineering application,which offers engineers an efficient,intuitive,immersive and integrated method for assembly process planning in a virtual environment.Based on analysis the information integration requirement of VAPP,the architecture of IVAPP is proposed.Through the integrated structure,IVAPP system can realize information integration and workflow controlling.In order to model the assembly process in IVAPP,a hierarchical assembly task list(HATL) is presented,in which different assembly tasks for assembling different components are organized into a hierarchical list.A process-oriented automatic geometrical constraint recognition algorithm(AGCR) is proposed,so that geometrical constraints between components can be automatically recognized during the process of interactive assembling.At the same time,a progressive hierarchical reasoning(PHR) model is discussed.AGCR and PHR will greatly reduce the interactive workload.A discrete control node model(DCNM) for cable harness assembly planning in IVAPP is detailed.DCNM converts a cable harness into continuous flexed line segments connected by a series of section center points,and designs can realize cable harness planning through controlling those control nodes.Mechanical assemblies(such as transmission case and engine of automobile) are used to illustrate the feasibility of the proposed method and algorithms.The application of IVAPP system reveals advantages over the traditional assembly process planning method in shortening the time-consumed in assembly planning and in minimizing the
