Design And Development Of Automatic Assembly System For Bolts And Nuts Used In Sets

In recent years,along with the increasing investment in energy,transportation and other infrastructure projects,various types of bolts and nuts fasteners are becoming increasingly needed and requirements on quality are enhanced.Bolts and nuts being hot dip galvanized are massively used in construction and assembly sites such as electric power steel tower,highway guardrail and etc.In most of above cases,the bolts and nuts should be matched in sets without thread damage,and interchanging is not allowed.Investigation on an automation system which can realize efficient assembly for bolts and nuts used in sets is becoming urgent need for industrial development,as the requirements increasing gradually.A special type of bolts and nuts(leveled with 4.8,specified as M16×45)applied in electric power steel tower was taken as the application object in this thesis.An automatic assembly system with stable performance and high efficiency was developed through theoretical analyzing,simulating and experimental prototype testing.The main research works of this thesis are summarized as follows:(1)The performance requirements and key indexes of automatic assembly system for bolts and nuts used in sets were determined according to the design requirements and criteria of automatic assembly system.The assembly process of automatic assembly system for bolts and nuts used in sets in this thesis was determined by analyzing and optimizing the assembly process of existing automatic assembly system.On this basis,the overall design scheme of mechanical structure,pneumatic circuit and control unit of the automatic assembly system were proposed,and the overall scheme of the system was designed.(2)Taking compact structure,strong and durable as one of the aims,and based on the overall design scheme of mechanical structure,the overall layout of mechanical structure and the automatic feeding mechanism were determined,as well as the other mechanisms including nut clamping and transport mechanism,bolt clamping and product discharging mechanism,bolts and nuts assembly mechanism.The composition and working principle of all mechanisms,design principles of key components and selection principles of actuators were described in detail.The strength of bolts and nuts fixtures were checked,and the mechanical structure ofautomatic assembly system was designed.(3)Taking stable operation,high efficiency and energy saving as one of the aims,and based on the overall design scheme of pneumatic circuit,mathematical model and simulation model of pneumatic circuit were established during the stroke and return process of cylinder.The influence of different diameters and different pressures on the acting time of cylinder was researched,to determine the pneumatic circuit pressure and pipe diameter.The mathematical model of the valve cylinder speed control loop including cylinder and proportional valve was established.The transfer function between the speed of cylinder piston and the control voltage of proportional valve was deduced,to provide the theoretical basis for the development of cylinder speed control function.(4)Taking convenient maintenance,monitoring and control integration as one of the aims,and based on the overall design scheme of control unit,hardware module and control flow were presented and FluidSIM was selected to verify the validity of control flow.The functional modules including fault self-diagnosis module,auto-calling module for shortage of material and remote monitoring module were developed to ensure the reliable operation of the system.(5)The prototype of automatic assembly system for bolts and nuts used in sets was trial-produced and assembled,the integrated test platform was built,and the test program was designed.On this basis,the functions and key performance indexes of the prototype were tested to verify the correctness of the system design.An automatic assembly system for bolts and nuts used in sets was designed and developed in this thesis by using the concept of machine-electric-gas integration.It can enhance assembling efficiency and reduce the rate of unqualified products.The study is a useful attempt for the machine-electric-gas integration design concept using in the product automation assembly system,and provides theoretical and technical basis for the development of domestic automatic assembly technology.