Design And Experimental Study Of Cable-Driven Parallel Mechanism For Building 3D Printing

Building 3D printing is a new building construction technology.It uses the computer to segment the model of the building to be printed,and converts the threedimensional graphic information into printing path and speed information,and then the numerical control program controls the printing equipment to lay materials layer by layer for printing and construction.Compared with traditional building construction methods,it has the advantages of environmental protection,energy saving,high quality,high efficiency,cost saving and construction safety.It conforms to the major strategic guidance of national green construction and has broad development prospects.However,the overall research and development of building 3D printing is not mature enough.The printing equipment only meets the construction of small houses,which is not competent for the integrated forming of high-rise buildings and industrialized mass production.Moreover,the equipment is too bulky to transport,install and adjust.The printing construction technology can not adapt to the irregular terrain on the site.Therefore,a3 D printing technology based on cable-driven parallel mechanism with large forming space,light weight,easy assembly and strong terrain adaptability is proposed in this paper.In order to realize the large forming space and lightweight design of cable-driven building printing system,this paper analyzes the degrees of freedom and motion types of cable-driven mechanism combined with the needs of building printing.The configuration of cable-driven mechanism is determined based on the configuration evolution method.The kinematics and statics of the designed cable-driven printing system are analyzed.The design basis of parameter optimization is constructed from four aspects: forming space,system stiffness,platform pose deviation caused by rope length deviation and motion/force transmission characteristics,and then the dimensional parameters of the end platform are determined.The software and hardware platform of cable-driven building printing is developed to provide physical devices for subsequent research.The designed cable-driven printing system can effectively avoid the interference between the cable and the printed object,and has good anti-interference ability and motion performance.In order to ensure the convenient installation,adjustment and reliable operation of cable-driven building printing system,the dynamic modeling of cable-driven building printing system is first established.Then,aiming at the problem that the redundant constraint type cable-driven mechanism is easy to produce driving interference,a driving strategy of cable-driven mechanism with unknown parameters based on deep deterministic policy gradient algorithm is proposed.In view of the complexity of the objective function of parameter identification of cable-driven mechanism,a BP neural network is proposed to map the relationship between pose deviation and mechanism parameter deviation.The method is verified by outdoor parameter identification experiments.In the aspect of motion control of cable-driven printing system,a position/ force hybrid motion control strategy is proposed,which is verified by simulation and experiment.The driving,identification and control methods of cable-driven printing system can ensure the effective sampling of identification data when the parameters of the mechanism are unknown,the automatic identification of mechanism parameters and the coordinated control of mechanism motion and tension.In order to reduce the influence of the characteristics of the cable-driven mechanism and external interference on the printing track,the interference inspection and adjustment strategy of the track is carried out based on the interference angle and interference triangle of the nozzle,and the interference free printing track is obtained.A crossing method of singular pose and driving interference pose based on finite difference is proposed to adjust the pose with strong singularity and driving interference on the trajectory.Aiming at the problem of nozzle flutter in cable-driven system,combined with differential evolution algorithm and BP neural network,the optimal acceleration and deceleration curves under different platform posture and rope tension are obtained to reduce the flutter amplitude of nozzle.Aiming at the problem of printing track deformation caused by gravity,a deformation model and compensation method are proposed to reduce the deformation degree of printing track under gravity.In order to verify the forming ability of the curved surface sample of the cabledriven printing system and improve the printing ability of the adaptive terrain of the system,firstly,the basic process parameters such as the reference linewidth,forming range,the maximum movement speed of the nozzle and the printing layer thickness range required for printing are determined through experiments,and then the printing experiments of the covering curved surface sample and the arched shell sample are carried out.Further,the influence law of irregular terrain on print line thickness,print line centerline offset and print layer height is studied,the quantitative model between them is established,and the corresponding compensation method is proposed.The effectiveness of the conformal printing method is verified by the experiment of conformal printing on irregular terrain.This paper studies the configuration design and parameter optimization,parameter identification and motion control,trajectory compensation and adjustment,curved surface sample printing and shape following printing of the cable-driven building printing system,so as to realize the large forming space and lightweight design of the cable-driven building printing system,ensure the convenient installation and reliable operation of the printing system,and improve the terrain adaptive printing ability of the printing system.